EP4706253A1

EP4706253A1 - Coding using multiple dynamic reference list types

Info

Publication number: EP4706253A1
Application number: EP24739786.2A
Authority: EP
Inventors: Jianle Chen; Debargha Mukherjee; Mohammed Golam Sarwer
Original assignee: Google LLC
Current assignee: Google LLC
Priority date: 2023-06-07
Filing date: 2024-06-05
Publication date: 2026-03-11
Also published as: WO2024254200A1

Abstract

Decoding using multiple dynamic reference list types includes obtaining reconstructed block data for a current block of a current frame of a sequence of frames, including the reconstructed block data in reconstructed frame data for the current frame, and including the reconstructed frame data in the reconstructed video data. Obtaining the reconstructed block data includes accessing, from the encoded bitstream, a signaled prediction mode identifier for decoding the current block, wherein the signaled prediction mode identifier indicates a compound prediction mode, in response to accessing the signaled prediction mode identifier, obtaining a dynamic reference list type value, obtaining, in accordance with the dynamic reference list type value, a first reference motion vector and a second reference motion vector, and obtaining a reconstructed current block by reconstructing the current block using the first reference motion vector and the second reference motion vector.

Description

CODING USING MULTIPLE DYNAMIC REFERENCE LIST TYPES

CROSS-REFERENCE TO RELATED APPLICATION^ )

[0001] This application claims priority to and the benefit of U.S. Provisional Application Patent Serial No. 63/471,527, filed June; 07, 2023, the entire disclosure of which is hereby incorporated by reference.

BACKGROUND

[0002] Digital images and video can be used, for example, on the internet, for remote business meetings via video conferencing, high-definition video entertainment, video advertisements, or sharing of user-generated content. Due to the large amount of data involved in transferring and processing image and video data, high-performance compression may be advantageous for transmission and storage. Accordingly, it would be advantageous to provide high-resolution image and video transmitted over communications channels having limited bandwidth.

SUMMARY

[0003] This application relates to encoding and decoding of image data, video stream data, or both for transmission, storage, or both. Disclosed herein are aspects of systems, methods, and apparatuses for encoding and decoding using multiple dynamic reference list types.

[0004] Variations in these and other aspects will be described in additional detail hereafter. [0005] An aspect is a method for decoding using multiple dynamic reference list types.

Decoding using multiple dynamic reference list types includes generating reconstructed video data by decoding an encoded bitstream and outputting the reconstructed video data. Decoding the encoded bitstream includes obtaining reconstructed block data for a current block of a current frame of a sequence of frames, including the reconstructed block data in reconstructed frame data for the current frame, and including the reconstructed frame data in the reconstructed video data. Obtaining the reconstructed block data includes accessing, from the encoded bitstream, a signaled prediction mode identifier for decoding the current block, wherein the signaled prediction mode identifier indicates a compound prediction mode, in response to accessing the signaled prediction mode identifier, obtaining a dynamic reference list type value, obtaining, in accordance with the dynamic reference list type value, a first reference motion vector and a second reference motion vector, and obtaining a reconstructed current block by reconstructing the current block using the first reference motion vector and the second reference motion vector.

[0006] An aspect is a non-transitory computer-readable storage medium storing an encoded bitstream comprising encoded block data for a current block of a current frame of a sequence of frames, data indicating a prediction mode identifier, wherein the prediction mode identifier indicates a compound prediction mode that includes using a first non-joint dynamic reference list and a second non-joint dynamic reference list to obtain motion vectors for obtaining reconstructed block data corresponding to the encoded block data, data indicating a first non-joint dynamic reference list index value with respect to the first non-joint dynamic reference list, and data indicating a second non-joint dynamic reference list index value with respect to the second non-joint dynamic reference list.

[0007] An aspect is a method for encoding using multiple dynamic reference list types. Encoding using multiple dynamic reference list types includes obtaining an encoded bitstream by encoding a current block of a current frame of a sequence of frames and outputting the encoded bitstream. Encoding the current block includes obtaining a prediction mode identifier indicating a prediction mode for encoding the current block, wherein the prediction mode is a compound prediction mode, obtaining a first motion vector for encoding the current block with reference to a first reference frame, obtaining a second motion vector for encoding the current block with reference to a second reference frame, obtaining a dynamic reference list type value, obtaining, in accordance with the dynamic reference list type value, a first reference motion vector and a second reference motion vector, encoding the first motion vector in accordance with the first reference motion vector, encoding the second motion vector in accordance with the second reference motion vector, and including data indicating the prediction mode identifier in the encoded bitstream.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views unless otherwise noted or otherwise clear from context.

[0009] FIG. 1 is a diagram of a computing device in accordance with implementations of this disclosure.

[0010] FIG. 2 is a diagram of a computing and communications system in accordance with implementations of this disclosure.

[0011] FIG. 3 is a diagram of a video stream for use in encoding and decoding in accordance with implementations of this disclosure.

[0012] FIG. 4 is a block diagram of an encoder in accordance with implementations of this disclosure.

[0013] FIG. 5 is a block diagram of a decoder in accordance with implementations of this disclosure.

[0014] FIG. 6 is a block diagram of a representation of a portion of a frame in accordance with implementations of this disclosure.

[0015] FIG. 7 is a block diagram of an example of encoding using multiple dynamic reference list types in accordance with implementations of this disclosure.

[0016] FIG. 8 is a flowchart diagram of an example of decoding using multiple dynamic reference list types in accordance with implementations of this disclosure.

DETAILED DESCRIPTION

[0017] Image and video compression schemes may include breaking an image, or frame, into smaller portions, such as blocks, and generating an output bitstream using techniques to minimize the bandwidth utilization of the information included for each block in the output. In some implementations, the information included for each block in the output may be limited by reducing spatial redundancy, reducing temporal redundancy, or a combination thereof. For example, temporal or spatial redundancies may be reduced by predicting a frame, or a portion thereof, based on information available to both the encoder and decoder, and including information representing a difference, or residual, between the predicted frame and the original frame in the encoded bitstream. The residual information may be further compressed by transforming the residual information into transform coefficients (e.g., energy compaction), quantizing the transform coefficients, and entropy coding the quantized transform coefficients. Other coding information, such as motion information, may be included in the encoded bitstream, which may include transmitting differential information based on predictions of the encoding information, which may be entropy coded to further reduce the corresponding bandwidth utilization. An encoded bitstream can be decoded to reconstruct the blocks and the source images from the limited information. In some implementations, the accuracy, efficiency, or both, of coding a block using either interprediction or intra-prediction may be limited.

[0018] Block-based hybrid video coding techniques, or codecs, to improve coding efficiency, predict a block of a frame either from one or more previously decoded, or reconstructed, frames ( inter prediction) or from the current frame (intra prediction). In inter prediction, a motion compensated prediction is obtained where a motion vector (MV) of a respective predicted block is generated. To decode an inter-predicted block, a decoder obtains, such as generates, a dynamic reference list (DRL), which is a list of reference motion vectors, and which is generated from the previously decoded neighboring blocks in the current frame and collocated blocks of the reference frame. The dynamic reference list includes a list of reference motion vectors of a prediction block.

[0019] To improve the signaling of the motion vector, directly signaling the motion vector is omitted and a difference between the reference motion vector and the motion vector used to obtain the predicted block is signaled (differential motion vector). To indicate the candidate reference motion vector from the dynamic reference list to use as the reference motion vector, an index value in the dynamic reference list corresponding to the candidate reference motion vector is signaled. In some inter prediction modes, the reference motion vector is used as the motion vector for coding the current block. In some inter prediction modes, the differential motion vector is signaled and a combination, or summation, of the differential motion vector and the reference motion vector is used as the motion vector for coding the current block.

[0020] Motion compensated prediction can be performed from one or more, such as two, reference frames. Compound motion compensated prediction (compound prediction) includes using two reference frames. In compound prediction modes (compound modes), two motion vectors are signaled. In non-compound prediction modes, a respective index value in the dynamic reference list corresponds with one candidate reference motion vector corresponding to one reference frame. In compound prediction modes, the dynamic reference list is a joint dynamic reference list wherein a respective index value in the joint dynamic reference list corresponds with two candidate reference motion vector, wherein a respective candidate reference motion vector corresponds with a respective reference frame.

[0021] The encoding and decoding using multiple dynamic reference list types described herein improves on video coding techniques, or codecs, by signaling a dynamic reference list type value for compound prediction modes, wherein the dynamic reference list type is joint dynamic reference list or non-joint dynamic reference list. For compound prediction modes wherein the non-joint dynamic reference list type is signaled, two non-joint dynamic reference lists are used, wherein a respective index value in a respective non-joint dynamic reference list corresponds with one candidate reference motion vector, wherein a first non- joint dynamic reference list index value is signaled to indicate a first reference motion vector (MVO) for a corresponding reference frame to be obtained from a first non-joint dynamic reference list (DRLO) and a second non-joint dynamic reference list index value is signaled to indicate a second reference motion vector (MV1) for a corresponding reference frame to be obtained from a second non-joint dynamic reference list (DRL1).

[0022] In some implementations, the dynamic reference list type value may be expressly signaled in the encoded bitstream. In some implementations, expressly signaling the dynamic reference list type value may be omitted, avoided, or excluded, and the dynamic reference list type value may be obtained in accordance with the compound prediction mode for the respective block. For example, two non-join, separate, or independent, dynamic reference lists may be used for a first defined, or configured, proper subset, or group, of compound prediction modes and a joint dynamic reference list may be used for a second defined, or configured, proper subset, or group, of compound prediction modes that includes the available compound prediction modes other than the compound prediction modes included in the first defined, or configured, proper subset, or group, of compound prediction modes. In some implementations, expressly signaling the dynamic reference list type value may be omitted, avoided, or excluded, and the dynamic reference list type value may be obtained in accordance with a size of the prediction block for coding the current block in accordance with a defined, or configured, block size. In some implementations, expressly signaling the dynamic reference list type value may be omitted, avoided, or excluded, and the dynamic reference list type value may be obtained in accordance with the size of joint dynamic reference list and non-joint dynamic reference lists.

[0023] FIG. 1 is a diagram of a computing device 100 in accordance with implementations of this disclosure. The computing device 100 shown includes a memory 110, a processor 120, a user interface (UI) 130, an electronic communication unit 140, a sensor 150, a power source 160, and a bus 170. As used herein, the term “computing device” includes any unit, or a combination of units, capable of performing any method, or any portion or portions thereof, disclosed herein.

[0024] The computing device 100 may be a stationary computing device, such as a personal computer (PC), a server, a workstation, a minicomputer, or a mainframe computer; or a mobile computing device, such as a mobile telephone, a personal digital assistant (PDA), a laptop, or a tablet PC. Although shown as a single unit, any one element or elements of the computing device 100 can be integrated into any number of separate physical units. For example, the user interface 130 and processor 120 can be integrated in a first physical unit and the memory 110 can be integrated in a second physical unit. [0025] The memory 110 can include any non-transitory computer-usable or computer- readable medium, such as any tangible device that can, for example, contain, store, communicate, or transport data 112, instructions 114, an operating system 116, or any information associated therewith, for use by or in connection with other components of the computing device 100. The non-transitory computer-usable or computer-readable medium can be, for example, a solid-state drive, a memory card, removable media, a read-only memory (ROM), a random-access memory (RAM), any type of disk including a hard disk, a floppy disk, an optical disk, a magnetic or optical card, an application- specific integrated circuits (ASICs), or any type of non-transitory media suitable for storing electronic information, or any combination thereof. For example, the non-transitory computer-readable storage medium may store an encoded bitstream.

[0026] Although shown a single unit, the memory 110 may include multiple physical units, such as one or more primary memory units, such as random-access memory units, one or more secondary data storage units, such as disks, or a combination thereof. For example, the data 112, or a portion thereof, the instructions 114, or a portion thereof, or both, may be stored in a secondary storage unit and may be loaded or otherwise transferred to a primary storage unit in conjunction with processing the respective data 112, executing the respective instructions 114, or both. In some implementations, the memory 110, or a portion thereof, may be removable memory.

[0027] The data 112 can include information, such as input audio data, encoded audio data, decoded audio data, or the like. The instructions 114 can include directions, such as code, for performing any method, or any portion or portions thereof, disclosed herein. The instructions 114 can be realized in hardware, software, or any combination thereof. For example, the instructions 114 may be implemented as information stored in the memory 110, such as a computer program, which may be executed by the processor 120 to perform any of the respective methods, algorithms, aspects, or combinations thereof, as described herein. [0028] Although shown as included in the memory 110, in some implementations, the instructions 114, or a portion thereof, may be implemented as a special purpose processor, or circuitry, that can include specialized hardware for carrying out any of the methods, algorithms, aspects, or combinations thereof, as described herein. Portions of the instructions 114 can be distributed across multiple processors on the same machine or different machines or across a network such as a local area network, a wide area network, the Internet, or a combination thereof.

[0029] The processor 120 can include any device or system capable of manipulating or processing a digital signal or other electronic information now-existing or hereafter developed, including optical processors, quantum processors, molecular processors, or a combination thereof. For example, the processor 120 can include a special purpose processor, a central processing unit (CPU), a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessor in association with a DSP core, a controller, a microcontroller, an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), a programmable logic array, programmable logic controller, microcode, firmware, any type of integrated circuit (IC), a state machine, or any combination thereof. As used herein, the term “processor” includes a single processor or multiple processors.

[0030] The user interface 130 can include any unit capable of interfacing with a user, such as a virtual or physical keypad, a touchpad, a display, a touch display, a speaker, a microphone, a video camera, a sensor, or any combination thereof. For example, the user interface 130 may be an audio-visual display device, and the computing device 100 may present audio, such as decoded audio, using the user interface 130 audio-visual display device, such as in conjunction with displaying video, such as decoded video. Although shown as a single unit, the user interface 130 may include one or more physical units. For example, the user interface 130 may include an audio interface for performing audio communication with a user, and a touch display for performing visual and touch-based communication with the user.

[0031] The electronic communication unit 140 can transmit, receive, or transmit and receive signals via a wired or wireless electronic communication medium 180, such as a radio frequency (RF) communication medium, an ultraviolet (UV) communication medium, a visible light communication medium, a fiber optic communication medium, a wireline communication medium, or a combination thereof. For example, as shown, the electronic communication unit 140 is operatively connected to an electronic communication interface 142, such as an antenna, configured to communicate via wireless signals.

[0032] Although the electronic communication interface 142 is shown as a wireless antenna in FIG. 1, the electronic communication interface 142 can be a wireless antenna, as shown, a wired communication port, such as an Ethernet port, an infrared port, a serial port, or any other wired or wireless unit capable of interfacing with a wired or wireless electronic communication medium 180. Although FIG. 1 shows a single electronic communication unit 140 and a single electronic communication interface 142, any number of electronic communication units and any number of electronic communication interfaces can be used.

[0033] The sensor 150 may include, for example, an audio-sensing device, a visible light- sensing device, a motion sensing device, or a combination thereof. For example, lOOthe sensor 150 may include a sound-sensing device, such as a microphone, or any other soundsensing device now existing or hereafter developed that can sense sounds in the proximity of the computing device 100, such as speech or other utterances, made by a user operating the computing device 100. In another example, the sensor 150 may include a camera, or any other image-sensing device now existing or hereafter developed that can sense an image such as the image of a user operating the computing device. Although a single sensor 150 is shown, the computing device 100 may include a number of sensors 150. For example, the computing device 100 may include a first camera oriented with a field of view directed toward a user of the computing device 100 and a second camera oriented with a field of view directed away from the user of the computing device 100.

[0034] The power source 160 can be any suitable device for powering the computing device 100. For example, the power source 160 can include a wired external power source interface; one or more dry cell batteries, such as nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion); solar cells; fuel cells; or any other device capable of powering the computing device 100. Although a single power source 160 is shown in FIG. 1, the computing device 100 may include multiple power sources 160, such as a battery and a wired external power source interface.

[0035] Although shown as separate units, the electronic communication unit 140, the electronic communication interface 142, the user interface 130, the power source 160, or portions thereof, may be configured as a combined unit. For example, the electronic communication unit 140, the electronic communication interface 142, the user interface 130, and the power source 160 may be implemented as a communications port capable of interfacing with an external display device, providing communications, power, or both.

[0036] One or more of the memory 110, the processor 120, the user interface 130, the electronic communication unit 140, the sensor 150, or the power source 160, may be operatively coupled via a bus 170. Although a single bus 170 is shown in FIG. 1, a computing device 100 may include multiple buses. For example, the memory 110, the processor 120, the user interface 130, the electronic communication unit 140, the sensor 150, and the bus 170 may receive power from the power source 160 via the bus 170. In another example, the memory 110, the processor 120, the user interface 130, the electronic communication unit 140, the sensor 150, the power source 160, or a combination thereof, may communicate data, such as by sending and receiving electronic signals, via the bus 170.

[0037] Although not shown separately in FIG. 1, one or more of the processor 120, the user interface 130, the electronic communication unit 140, the sensor 150, or the power source 160 may include internal memory, such as an internal buffer or register. For example, the processor 120 may include internal memory (not shown) and may read data 112 from the memory 110 into the internal memory (not shown) for processing.

[0038] Although shown as separate elements, the memory 110, the processor 120, the user interface 130, the electronic communication unit 140, the sensor 150, the power source 160, and the bus 170, or any combination thereof can be integrated in one or more electronic units, circuits, or chips.

[0039] FIG. 2 is a diagram of a computing and communications system 200 in accordance with implementations of this disclosure. The computing and communications system 200 shown includes computing and communication devices 100A, 100B, 100C, access points 210A, 210B, and a network 220. For example, the computing and communication system 200 can be a multiple access system that provides communication, such as voice, audio, data, video, messaging, broadcast, or a combination thereof, to one or more wired or wireless communicating devices, such as the computing and communication devices 100A, 100B, 100C. Although, for simplicity, FIG. 2 shows three computing and communication devices 100A, 100B, 100C, two access points 210A, 210B, and one network 220, any number of computing and communication devices, access points, and networks can be used.

[0040] A computing and communication device 100A, 100B, 100C can be, for example, a computing device, such as the computing device 100 shown in FIG. 1. For example, the computing and communication devices 100A, 100B may be user devices, such as a mobile computing device, a laptop, a thin client, or a smartphone, and the computing and communication device 100C may be a server, such as a mainframe or a cluster. Although the computing and communication device 100A and the computing and communication device 100B are described as user devices, and the computing and communication device 100C is described as a server, any computing and communication device may perform some or all of the functions of a server, some, or all, of the functions of a user device, or some or all of the functions of a server and a user device. For example, the server computing and communication device 100C may receive, encode, process, store, transmit, or a combination thereof audio data and one or both of the computing and communication device 100A and the computing and communication device 100B may receive, decode, process, store, present, or a combination thereof the audio data.

[0041] Each computing and communication device 100A, 100B, 100C, which may include a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a cellular telephone, a personal computer, a tablet computer, a server, consumer electronics, or any similar device, can be configured to perform wired or wireless communication, such as via the network 220. For example, the computing and communication devices 100A, 100B, 100C can be configured to transmit or receive wired or wireless communication signals. Although each computing and communication device 100A, 100B, 100C is shown as a single unit, a computing and communication device can include any number of interconnected elements. [0042] Each access point 210A, 210B can be any type of device configured to communicate with a computing and communication device 100A, 100B, 100C, a network 220, or both via wired or wireless communication links 180A, 180B, 180C. For example, an access point 210A, 210B can include a base station, a base transceiver station (BTS), a Node- B, an enhanced Node-B (eNode-B), a Home Node-B (HNode-B), a wireless router, a wired router, a hub, a relay, a switch, or any similar wired or wireless device. Although each access point 210A, 210B is shown as a single unit, an access point can include any number of interconnected elements.

[0043] The network 220 can be any type of network configured to provide services, such as voice, data, applications, voice over internet protocol (VoIP), or any other communications protocol or combination of communications protocols, over a wired or wireless communication link. For example, the network 220 can be a local area network (LAN), wide area network (WAN), virtual private network (VPN), a mobile or cellular telephone network, the Internet, or any other means of electronic communication. The network can use a communication protocol, such as the transmission control protocol (TCP), the user datagram protocol (UDP), the internet protocol (IP), the real-time transport protocol (RTP) the HyperText Transport Protocol (HTTP), or a combination thereof.

[0044] The computing and communication devices 100A, 100B, 100C can communicate with each other via the network 220 using one or more a wired or wireless communication links, or via a combination of wired and wireless communication links. For example, as shown the computing and communication devices 100A, 100B can communicate via wireless communication links 180A, 180B, and computing and communication device 100C can communicate via a wired communication link 180C. Any of the computing and communication devices 100A, 100B, 100C may communicate using any wired or wireless communication link, or links. For example, a first computing and communication device 100A can communicate via a first access point 210A using a first type of communication link, a second computing and communication device 100B can communicate via a second access point 210B using a second type of communication link, and a third computing and communication device 100C can communicate via a third access point (not shown) using a third type of communication link. Similarly, the access points 210A, 210B can communicate with the network 220 via one or more types of wired or wireless communication links 230A, 230B. Although FIG. 2 shows the computing and communication devices 100A, 100B, 100C in communication via the network 220, the computing and communication devices 100A, 100B, 100C can communicate with each other via any number of communication links, such as a direct wired or wireless communication link.

[0045] In some implementations, communications between one or more of the computing and communication device 100A, 100B, 100C may omit communicating via the network 220 and may include transferring data via another medium (not shown), such as a data storage device. For example, the server computing and communication device 100C may store audio data, such as encoded audio data, in a data storage device, such as a portable data storage unit, and one or both of the computing and communication device 100A or the computing and communication device 100B may access, read, or retrieve the stored audio data from the data storage unit, such as by physically disconnecting the data storage device from the server computing and communication device 100C and physically connecting the data storage device to the computing and communication device 100A or the computing and communication device 100B.

[0046] Other implementations of the computing and communications system 200 are possible. For example, in an implementation, the network 220 can be an ad-hoc network and can omit one or more of the access points 210A, 210B. The computing and communications system 200 may include devices, units, or elements not shown in FIG. 2. For example, the computing and communications system 200 may include many more communicating devices, networks, and access points.

[0047] FIG. 3 is a diagram of a video stream 300 for use in encoding and decoding in accordance with implementations of this disclosure. A video stream 300, such as a video stream captured by a video camera or a video stream generated by a computing device, may include a video sequence 310. The video sequence 310 may include a sequence of adjacent frames 320. Although three adjacent frames 320 are shown, the video sequence 310 can include any number of adjacent frames 320.

[0048] Each frame 330 from the adjacent frames 320 may represent a single image from the video stream. Although not shown in FIG. 3, a frame 330 may include one or more segments, tiles, or planes, which may be coded, or otherwise processed, independently, such as in parallel. A frame 330 may include one or more tiles 340. Each of the tiles 340 may be a rectangular region of the frame that can be coded independently. Each of the tiles 340 may include respective blocks 350. Although not shown in FIG. 3, a block can include pixels. For example, a block can include a 16x16 group of pixels, an 8x8 group of pixels, an 8x16 group of pixels, or any other group of pixels. Unless otherwise indicated herein, the term ‘block’ can include a superblock, a macroblock, a segment, a slice, or any other portion of a frame. A frame, a block, a pixel, or a combination thereof can include display information, such as luminance information, chrominance information, or any other information that can be used to store, modify, communicate, or display the video stream or a portion thereof.

[0049] FIG. 4 is a block diagram of an encoder 400 in accordance with implementations of this disclosure. Encoder 400 can be implemented in a device, such as the computing device 100 shown in FIG. 1 or the computing and communication devices 100A, 100B, 100C shown in FIG. 2, as, for example, a computer software program stored in a data storage unit, such as the memory 110 shown in FIG. 1. The computer software program can include machine instructions that may be executed by a processor, such as the processor 120 shown in FIG. 1, and may cause the device to encode video data as described herein. The encoder 400 can be implemented as specialized hardware included, for example, in computing device 100.

[0050] The encoder 400 can encode an input video stream 402, such as the video stream 300 shown in FIG. 3, to generate an encoded (compressed) bitstream 404. In some implementations, the encoder 400 may include a forward path for generating the compressed bitstream 404. The forward path may include an intra/inter prediction unit 410, a transform unit 420, a quantization unit 430, an entropy encoding unit 440, or any combination thereof. In some implementations, the encoder 400 may include a reconstruction path (indicated by the broken connection lines) to reconstruct a frame for encoding of further blocks. The reconstruction path may include a dequantization unit 450, an inverse transform unit 460, a reconstruction unit 470, a filtering unit 480, or any combination thereof. Other structural variations of the encoder 400 can be used to encode the video stream 402.

[0051] For encoding the video stream 402, each frame within the video stream 402 can be processed in units of blocks. Thus, a current block may be identified from the blocks in a frame, and the current block may be encoded.

[0052] At the intra/inter prediction unit 410, the current block can be encoded using either intra-frame prediction, which may be within a single frame, or inter-frame prediction, which may be from frame to frame. Intra-prediction may include generating a prediction block from samples in the current frame that have been previously encoded and reconstructed. Interprediction may include generating a prediction block from samples in one or more previously constructed reference frames. Generating a prediction block for a current block in a current frame may include performing motion estimation to generate a motion vector indicating an appropriate reference portion of the reference frame.

[0053] The intra/inter prediction unit 410 may subtract the prediction block from the current block (raw block) to produce a residual block. The transform unit 420 may perform a block-based transform, which may include transforming the residual block into transform coefficients in, for example, the frequency domain. Examples of block-based transforms include the Karhunen-Loeve Transform (KLT), the Discrete Cosine Transform (DCT), the Singular Value Decomposition Transform (SVD), and the Asymmetric Discrete Sine Transform (ADST). In an example, the DCT may include transforming a block into the frequency domain. The DCT may include using transform coefficient values based on spatial frequency, with the lowest frequency (i.e., DC) coefficient at the top-left of the matrix and the highest frequency coefficient at the bottom-right of the matrix.

[0054] The quantization unit 430 may convert the transform coefficients into discrete quantum values, which may be referred to as quantized transform coefficients or quantization levels. The quantized transform coefficients can be entropy encoded by the entropy encoding unit 440 to produce entropy-encoded coefficients. Entropy encoding can include using a probability distribution metric. The entropy-encoded coefficients and information used to decode the block, which may include the type of prediction used, motion vectors, and quantizer values, can be output to the compressed bitstream 404. The compressed bitstream 404 can be formatted using various techniques, such as run-length encoding (RLE) and zerorun coding.

[0055] The reconstruction path can be used to maintain reference frame synchronization between the encoder 400 and a corresponding decoder, such as the decoder 500 shown in FIG. 5. The reconstruction path may be similar to the decoding process discussed below and may include decoding the encoded frame, or a portion thereof, which may include decoding an encoded block, which may include dequantizing the quantized transform coefficients at the dequantization unit 450 and inverse transforming the dequantized transform coefficients at the inverse transform unit 460 to produce a derivative residual block. The reconstruction unit 470 may add the prediction block generated by the intra/inter prediction unit 410 to the derivative residual block to create a decoded block. The filtering unit 480 can be applied to the decoded block to generate a reconstructed block, which may reduce distortion, such as blocking artifacts. Although one filtering unit 480 is shown in FIG. 4, filtering the decoded block may include loop filtering, deblocking filtering, or other types of filtering or combinations of types of filtering. The reconstructed block may be stored or otherwise made accessible as a reconstructed block, which may be a portion of a reference frame, for encoding another portion of the current frame, another frame, or both, as indicated by the broken line at 482. Coding information, such as deblocking threshold index values, for the frame may be encoded, included in the compressed bitstream 404, or both, as indicated by the broken line at 484.

[0056] Other variations of the encoder 400 can be used to encode the compressed bitstream 404. For example, a non-transform-based encoder 400 can quantize the residual block directly without the transform unit 420. In some implementations, the quantization unit 430 and the dequantization unit 450 may be combined into a single unit.

[0057] FIG. 5 is a block diagram of a decoder 500 in accordance with implementations of this disclosure. The decoder 500 can be implemented in a device, such as the computing device 100 shown in FIG. 1 or the computing and communication devices 100A, 100B, 100C shown in FIG. 2, as, for example, a computer software program stored in a data storage unit, such as the memory 110 shown in FIG. 1. The computer software program can include machine instructions that may be executed by a processor, such as the processor 120 shown in FIG. 1, and may cause the device to decode video data as described herein. The decoder 500 can be implemented as specialized hardware included, for example, in computing device 100.

[0058] The decoder 500 may receive a compressed bitstream 502, such as the compressed bitstream 404 shown in FIG. 4, and may decode the compressed bitstream 502 to generate an output video stream 504. The decoder 500 may include an entropy decoding unit 510, a dequantization unit 520, an inverse transform unit 530, an intra/inter prediction unit 540, a reconstruction unit 550, a filtering unit 560, or any combination thereof. Other structural variations of the decoder 500 can be used to decode the compressed bitstream 502.

[0059] The entropy decoding unit 510 may decode data elements within the compressed bitstream 502 using, for example, Context Adaptive Binary Arithmetic Decoding, to produce a set of quantized transform coefficients. The dequantization unit 520 can dequantize the quantized transform coefficients, and the inverse transform unit 530 can inverse transform the dequantized transform coefficients to produce a derivative residual block, which may correspond to the derivative residual block generated by the inverse transform unit 460 shown in FIG. 4. Using header information decoded from the compressed bitstream 502, the intra/inter prediction unit 540 may generate a prediction block corresponding to the prediction block created in the encoder 400. At the reconstruction unit 550, the prediction block can be added to the derivative residual block to create a decoded block. The filtering unit 560 can be applied to the decoded block to reduce artifacts, such as blocking artifacts, which may include loop filtering, deblocking filtering, or other types of filtering or combinations of types of filtering, and which may include generating a reconstructed block, which may be output as the output video stream 504.

[0060] Other variations of the decoder 500 can be used to decode the compressed bitstream 502. For example, the decoder 500 can produce the output video stream 504 without the deblocking filtering unit 570.

[0061] FIG. 6 is a block diagram of a representation of a portion 600 of a frame, such as the frame 330 shown in FIG. 3, in accordance with implementations of this disclosure. As shown, the portion 600 of the frame includes four 64x64 blocks 610, in two rows and two columns in a matrix or Cartesian plane. In some implementations, a 64x64 block may be a maximum coding unit, N=64. Each 64x64 block may include four 32x32 blocks 620. Each 32x32 block may include four 16x16 blocks 630. Each 16x16 block may include four 8x8 blocks 640. Each 8x8 block 640 may include four 4x4 blocks 650. Each 4x4 block 650 may include 16 pixels, which may be represented in four rows and four columns in each respective block in the Cartesian plane or matrix. The pixels may include information representing an image captured in the frame, such as luminance information, color information, and location information. In some implementations, a block, such as a 16x16 pixel block as shown, may include a luminance block 660, which may include luminance pixels 662; and two chrominance blocks 670, 680, such as a U or Cb chrominance block 670, and a V or Cr chrominance block 680. The chrominance blocks 670, 680 may include chrominance pixels 690. For example, the luminance block 660 may include 16x16 luminance pixels 662 and each chrominance block 670, 680 may include 8x8 chrominance pixels 690 as shown. Although one arrangement of blocks is shown, any arrangement may be used. Although FIG.

6 shows NxN blocks, in some implementations, NxM blocks may be used. For example, 32x64 blocks, 64x32 blocks, 16x32 blocks, 32x16 blocks, or any other size blocks may be used. In some implementations, Nx2N blocks, 2NxN blocks, or a combination thereof may be used.

[0062] In some implementations, video coding may include ordered block-level coding. Ordered block-level coding may include coding blocks of a frame in an order, such as rasterscan order, wherein blocks may be identified and processed starting with a block in the upper left comer of the frame, or portion of the frame, and proceeding along rows from left to right and from the top row to the bottom row, identifying each block in turn for processing. For example, the 64x64 block in the top row and left column of a frame may be the first block coded and the 64x64 block immediately to the right of the first block may be the second block coded. The second row from the top may be the second row coded, such that the 64x64 block in the left column of the second row may be coded after the 64x64 block in the rightmost column of the first row.

[0063] In some implementations, coding a block may include using quad-tree coding, which may include coding smaller block units within a block in raster- scan order. For example, the 64x64 block shown in the bottom left comer of the portion of the frame shown in FIG. 6, may be coded using quad-tree coding wherein the top left 32x32 block may be coded, then the top right 32x32 block may be coded, then the bottom left 32x32 block may be coded, and then the bottom right 32x32 block may be coded. Each 32x32 block may be coded using quad- tree coding wherein the top left 16x16 block may be coded, then the top right 16x16 block may be coded, then the bottom left 16x16 block may be coded, and then the bottom right 16x16 block may be coded. Each 16x16 block may be coded using quad- tree coding wherein the top left 8x8 block may be coded, then the top right 8x8 block may be coded, then the bottom left 8x8 block may be coded, and then the bottom right 8x8 block may be coded. Each 8x8 block may be coded using quad-tree coding wherein the top left 4x4 block may be coded, then the top right 4x4 block may be coded, then the bottom left 4x4 block may be coded, and then the bottom right 4x4 block may be coded. In some implementations, 8x8 blocks may be omitted for a 16x16 block, and the 16x16 block may be coded using quad-tree coding wherein the top left 4x4 block may be coded, then the other 4x4 blocks in the 16x16 block may be coded in raster- scan order.

[0064] In some implementations, video coding may include compressing the information included in an original, or input, frame by, for example, omitting some of the information in the original frame from a corresponding encoded frame. For example, coding may include reducing spectral redundancy, reducing spatial redundancy, reducing temporal redundancy, or a combination thereof.

[0065] In some implementations, reducing spectral redundancy may include using a color model based on a luminance component (Y) and two chrominance components (U and V or Cb and Cr), which may be referred to as the YUV or YCbCr color model, or color space. Using the YUV color model may include using a relatively large amount of information to represent the luminance component of a portion of a frame and using a relatively small amount of information to represent each corresponding chrominance component for the portion of the frame. For example, a portion of a frame may be represented by a high- resolution luminance component, which may include a 16x16 block of pixels, and by two lower resolution chrominance components, each of which represents the portion of the frame as an 8x8 block of pixels. A pixel may indicate a value, for example, a value in the range from 0 to 255, and may be stored or transmitted using, for example, eight bits. Although this disclosure is described in reference to the YUV color model, any color model may be used. [0066] In some implementations, reducing spatial redundancy may include transforming a block into the frequency domain using, for example, a discrete cosine transform (DCT). For example, a unit of an encoder, such as the transform unit 420 shown in FIG. 4, may perform a DCT using transform coefficient values based on spatial frequency.

[0067] In some implementations, reducing temporal redundancy may include using similarities between frames to encode a frame using a relatively small amount of data based on one or more reference frames, which may be previously encoded, decoded, and reconstructed frames of the video stream. For example, a block or pixel of a current frame may be similar to a spatially corresponding block or pixel of a reference frame. In some implementations, a block or pixel of a current frame may be similar to block or pixel of a reference frame at a different spatial location and reducing temporal redundancy may include generating motion information indicating the spatial difference, or translation, between the location of the block or pixel in the current frame and corresponding location of the block or pixel in the reference frame.

[0068] In some implementations, reducing temporal redundancy may include identifying a portion of a reference frame that corresponds to a current block or pixel of a current frame. For example, a reference frame, or a portion of a reference frame, which may be stored in memory, may be searched to identify a portion for generating a prediction to use for encoding a current block or pixel of the current frame with maximal efficiency. For example, the search may identify a portion of the reference frame for which the difference in pixel values between the current block and a prediction block generated based on the portion of the reference frame is minimized and may be referred to as motion searching. In some implementations, the portion of the reference frame searched may be limited. For example, the portion of the reference frame searched, which may be referred to as the search area, may include a limited number of rows of the reference frame. In an example, identifying the portion of the reference frame for generating a prediction may include calculating a cost function, such as a sum of absolute differences (SAD), between the pixels of portions of the search area and the pixels of the current block.

[0069] In some implementations, the spatial difference between the location of the portion of the reference frame for generating a prediction in the reference frame and the current block in the current frame may be represented as a motion vector. The difference in pixel values between the prediction block and the current block may be referred to as differential data, residual data, a prediction error, or as a residual block. In some implementations, generating motion vectors may be referred to as motion estimation, and a pixel of a current block may be indicated based on location using Cartesian coordinates as /_x, _y. Similarly, a pixel of the search area of the reference frame may be indicated based on location using Cartesian coordinates as r_x, _y. A motion vector (MV) for the current block may be determined based on, for example, a SAD between the pixels of the current frame and the corresponding pixels of the reference frame.

[0070] Although described herein with reference to matrix or Cartesian representation of a frame for clarity, a frame may be stored, transmitted, processed, or any combination thereof, in any data structure such that pixel values may be efficiently represented for a frame or image. For example, a frame may be stored, transmitted, processed, or any combination thereof, in a two-dimensional data structure such as a matrix as shown, or in a onedimensional data structure, such as a vector array. In an implementation, a representation of the frame, such as a two-dimensional representation as shown, may correspond to a physical location in a rendering of the frame as an image. For example, a location in the top left corner of a block in the top left comer of the frame may correspond with a physical location in the top left corner of a rendering of the frame as an image.

[0071] In some implementations, block-based coding efficiency may be improved by partitioning input blocks into one or more prediction partitions, which may be rectangular, including square, partitions for prediction coding. In some implementations, video coding using prediction partitioning may include selecting a prediction partitioning scheme from among multiple candidate prediction partitioning schemes. For example, in some implementations, candidate prediction partitioning schemes for a 64x64 coding unit may include rectangular size prediction partitions ranging in sizes from 4x4 to 64x64, such as 4x4, 4x8, 8x4, 8x8, 8x16, 16x8, 16x16, 16x32, 32x16, 32x32, 32x64, 64x32, or 64x64. In some implementations, video coding using prediction partitioning may include a full prediction partition search, which may include selecting a prediction partitioning scheme by encoding the coding unit using each available candidate prediction partitioning scheme and selecting the best scheme, such as the scheme that produces the least rate-distortion error. [0072] In some implementations, encoding a video frame may include identifying a prediction partitioning scheme for encoding a current block, such as block 610. In some implementations, identifying a prediction partitioning scheme may include determining whether to encode the block as a single prediction partition of maximum coding unit size, which may be 64x64 as shown, or to partition the block into multiple prediction partitions, which may correspond with the sub-blocks, such as the 32x32 blocks 620 the 16x16 blocks 630, or the 8x8 blocks 640, as shown, and may include determining whether to partition into one or more smaller prediction partitions. For example, a 64x64 block may be partitioned into four 32x32 prediction partitions. Three of the four 32x32 prediction partitions may be encoded as 32x32 prediction partitions and the fourth 32x32 prediction partition may be further partitioned into four 16x16 prediction partitions. Three of the four 16x16 prediction partitions may be encoded as 16x16 prediction partitions and the fourth 16x16 prediction partition may be further partitioned into four 8x8 prediction partitions, each of which may be encoded as an 8x8 prediction partition. In some implementations, identifying the prediction partitioning scheme may include using a prediction partitioning decision tree.

[0073] In some implementations, video coding for a current block may include identifying an optimal prediction coding mode from multiple candidate prediction coding modes, which may provide flexibility in handling video signals with various statistical properties and may improve the compression efficiency. For example, a video coder may evaluate each candidate prediction coding mode to identify the optimal prediction coding mode, which may be, for example, the prediction coding mode that minimizes an error metric, such as a rate-distortion cost, for the current block. In some implementations, the complexity of searching the candidate prediction coding modes may be reduced by limiting the set of available candidate prediction coding modes based on similarities between the current block and a corresponding prediction block. In some implementations, the complexity of searching each candidate prediction coding mode may be reduced by performing a directed refinement mode search. For example, metrics may be generated for a limited set of candidate block sizes, such as 16x16, 8x8, and 4x4, the error metric associated with each block size may be in descending order, and additional candidate block sizes, such as 4x8 and 8x4 block sizes, may be evaluated.

[0074] In some implementations, block-based coding efficiency may be improved by partitioning a current residual block into one or more transform partitions, which may be rectangular, including square, partitions for transform coding. In some implementations, video coding, such as video coding using transform partitioning, may include selecting a uniform transform partitioning scheme. For example, a current residual block, such as block 610, may be a 64x64 block and may be transformed without partitioning using a 64x64 transform.

[0075] Although not expressly shown in FIG. 6, a residual block may be transform partitioned using a uniform transform partitioning scheme. For example, a 64x64 residual block may be transform partitioned using a uniform transform partitioning scheme including four 32x32 transform blocks, using a uniform transform partitioning scheme including sixteen 16x16 transform blocks, using a uniform transform partitioning scheme including sixty-four 8x8 transform blocks, or using a uniform transform partitioning scheme including 256 4x4 transform blocks.

[0076] In some implementations, video coding, such as video coding using transform partitioning, may include identifying multiple transform block sizes for a residual block using multiform transform partition coding. In some implementations, multiform transform partition coding may include recursively determining whether to transform a current block using a current block size transform or by partitioning the current block and multiform transform partition coding each partition. For example, the bottom left block 610 shown in FIG. 6 may be a 64x64 residual block, and multiform transform partition coding may include determining whether to code the current 64x64 residual block using a 64x64 transform or to code the 64x64 residual block by partitioning the 64x64 residual block into partitions, such as four 32x32 blocks 620, and multiform transform partition coding each partition. In some implementations, determining whether to transform partition the current block may be based on comparing a cost for encoding the current block using a current block size transform to a sum of costs for encoding each partition using partition size transforms.

[0077] FIG. 7 is a block diagram of an example of encoding using multiple dynamic reference list types 700. Encoding using multiple dynamic reference list types 700 may be implemented by an encoder, such as the encoder 400 shown in FIG. 4.

[0078] Encoding using multiple dynamic reference list types 700 includes encoding an input video steam, such as the input video stream 402 shown in FIG. 4, or one or more portions thereof, to generate an encoded (compressed) output bitstream, such as the encoded (compressed) bitstream 404 shown in FIG. 4.

[0079] In block-based hybrid video coding, to reduce, or minimize, the resource utilization, such as bandwidth utilization, for signaling, storing, or both, compressed, or encoded, video data, redundant data, such as spatially redundant data, temporally redundant data, or both, is omitted or excluded from the compressed, or encoded, data.

[0080] Encoding using multiple dynamic reference list types 700 includes obtaining a input video data (at 710), obtaining a current frame and a current block (at 720), obtaining a prediction mode (at 730), obtaining a dynamic reference list type value (at 740), obtaining reference motion vectors (at 750), obtaining encoded block data (at 760), and outputting the encoded bitstream (at 770). Although not shown expressly in FIG. 7, encoding using multiple dynamic reference list types 700 includes other aspects of video coding.

[0081] The input video data is obtained (at 710). The input video data includes a sequence of frames (input frames). For example, the encoder, or a component thereof, such as an intra/inter prediction unit of the encoder, such as the intra/inter prediction unit 410 shown in FIG. 4, may obtain the input video stream.

[0082] The current frame for encoding is obtained (at 720) from the sequence of frames from the input video data. The current frame may be obtained (at 720) subsequent to encoding one or more other frames, such as a frame sequentially preceding the current frame in the input video stream, and generating, or otherwise obtaining, a corresponding reconstructed frame (or frames), or one or more portions thereof, for use as a reference frame (or frames) for encoding the current frame.

[0083] The current block for encoding is obtained (at 720) from the current frame. The current block may be obtained (at 720) subsequent to encoding one or more other block, such as a block sequentially preceding the current block in the current frame, in accordance with a block coding order for coding the current frame, and generating, or otherwise obtaining, a corresponding reconstructed block, or one or more portions thereof, for use as a reference block for encoding the current block.

[0084] Although not shown expressly in FIG. 7, encoding using multiple dynamic reference list types 700 includes obtaining, maintaining, or both, a decoded frame buffer. One or more of the frames in the decoded frame buffer may be reference frames, such as decoded, or reconstructed, reference frames, constructed, or alternative, reference frames, or both. The decoded frame buffer may have a defined size, such as eight (8), indicating a maximum number, count, or cardinality, of decoded frames included in, or that may be included in, the decoded frame buffer. A respective reference frame from the decoded frame buffer may be indicated, or identified, by a corresponding decoded frame buffer index value.

[0085] The prediction mode for coding the current block is obtained (at 730). The prediction mode is obtained, or identified, using a rate-distortion optimization procedure. The prediction mode is an intra prediction mode or an inter prediction mode. For encoding using multiple dynamic reference list types 700, the prediction mode is an inter prediction mode. The encoder signals the prediction mode by including, in the encoded bitstream, a prediction mode identifier corresponding to the prediction mode.

[0086] In inter prediction, a motion compensated prediction (prediction block) of the current block is obtained, such as generated. The prediction block is obtained, or generated, in accordance with one or more motion vectors and one or more reference frames, such as the reference frames indicated in the decoded frame buffer. To obtain a respective motion vector, the encoder obtains, such as generates, a corresponding reference, or prediction, motion vector. For some inter prediction modes, such as a NEAR, or NEARMV, inter prediction mode, the encoder uses the reference motion vector as the motion vector for encoding the current block. For some inter prediction modes, such as a NEW, or NEWMV, inter prediction mode, the encoder obtains, such as determines, the motion vector for encoding the current block, and obtains, such as generates, as a differential motion vector, a result of subtracting the reference motion vector from the motion vector for encoder the current block.

[0087] The inter prediction mode may be a non-compound inter prediction mode or a compound inter prediction mode. In implementations of encoding using multiple dynamic reference list types 700, the prediction mode is a compound inter prediction mode.

[0088] Compound prediction, or compound inter prediction, includes obtaining predicted sample values by blending together predictions from multiple, such as two (2), reference frames, including a first reference frame and a second reference frame. In some implementations, the second reference frame may be the first reference frame. In some implementations, the second reference frame may differ from the first reference frame. In compound prediction, multiple, such as two (2), motion vectors are signaled in the encoded bitstream.

[0089] The compound inter prediction mode, or compound prediction mode, is one of one or more available compound prediction modes. The available compound prediction modes may include a defined number, count, or cardinality, of available compound prediction modes, such as thirteen (13) available compound prediction modes. For example, the available compound prediction modes may include a NEAR_NEARMV compound prediction mode, a NEAR_NEWMV compound prediction mode, a NEW_NEARMV compound prediction mode, a GLOB AL_GLOB ALM V compound prediction mode, a NEW_NEWMV compound prediction mode, a JOINT_NEWMV compound prediction mode, a JOINT_AMVDNEWMV compound prediction mode, a NEAR_NEARMV_OPTFLOW compound prediction mode, a NEAR_NEWMV_OPTFLOW compound prediction mode, a NEW_NEARMV_OPTFLOW compound prediction mode, a NEW_NEWMV_OPTFLOW compound prediction mode, a JOINT_NEWMV_OPTFLOW compound prediction mode, and a JOINT_AMVDNEWMV_OPTFLOW compound prediction mode.

[0090] The dynamic reference list type value is obtained (at 740). The dynamic reference list type value indicates whether encoding the current block includes obtaining, such as by generating, a joint dynamic reference list or two non-joint dynamic reference lists.

[0091] Obtaining the dynamic reference list type value (at 740) includes obtaining, such as by generating, one or more dynamic reference lists and identifying the dynamic reference list type value corresponding to one or more of the dynamic reference lists. A respective dynamic reference list may have a defined size, indicating a defined number, count, or cardinality, such as three (3) or four (4), of reference motion vectors, or reference motion vector pairs included in the respective dynamic reference list.

[0092] In some implementations, encoding the current block includes obtaining, such as by generating, the joint dynamic reference list for encoding the current block, and the dynamic reference list type value is the first dynamic reference list type value.

[0093] In some implementations, encoding the current block includes obtaining, such as by generating, the two non-joint dynamic reference lists for encoding the current block, and the dynamic reference list type value is the second dynamic reference list type value.

[0094] Generating, or otherwise obtaining, a respective dynamic reference list includes obtaining one or more reference motion vectors from one or more context blocks, such as previously encoded and reconstructed, blocks neighboring, or immediately adjacent to, the current block, such as above the current block, to the left of the current block, or above and to the left of the current block, or otherwise preceding the current block in a block coding order or sequence used for coding the current frame (spatial neighboring blocks in the current frame), or in a collocated block from a reference frame, at a location equivalent to, concurrent with, or corresponding to, a location of the current block in the current frame (temporal neighboring blocks in a reference frame), wherein the reference motion vector was, or the reference motion vectors were, used for obtaining, such as by generating, the respective encoded block.

[0095] Obtaining reference motion vectors (at 750) includes including, in the encoded bitstream, one or more dynamic reference list index values.

[0096] In some implementations, encoding the current block includes obtaining, such as by generating, the joint dynamic reference list for encoding the current block, and including, in the encoded bitstream, one or more signaled dynamic reference list index values, includes including, in the encoded bitstream, a joint dynamic reference list index value with respect to the joint dynamic reference list.

[0097] In some implementations, encoding the current block includes obtaining, such as by generating, the two non-joint dynamic reference lists for encoding the current block, and including, in the encoded bitstream, one or more dynamic reference list index values, includes including, in the encoded bitstream, a first non-joint dynamic reference list index value with respect to the first non-joint dynamic reference list, and a second non-joint dynamic reference list index value with respect to the second non-joint dynamic reference list. In some implementations, the second non-joint dynamic reference list index value may be signaled differentially with respect to the first non-joint dynamic reference list index value.

[0098] A first dynamic reference list type value indicates that encoding the current block includes obtaining, such as by generating, the joint dynamic reference list for encoding the current block. In some implementations, the first dynamic reference list type value indicates that encoding the current block omits, avoids, or excludes obtaining non-joint dynamic reference lists.

[0099] A second dynamic reference list type value indicates that encoding the current block includes obtaining, such as by generating, non-joint dynamic reference lists for encoding the current block. In some implementations, the second dynamic reference list type value indicates that encoding the current block omits, avoids, or excludes obtaining the joint dynamic reference list.

[0100] In a non-compound inter prediction mode, the dynamic reference list, which is a non-joint dynamic reference list, includes one or more candidate reference motion vectors. A respective candidate reference motion vector is associated with, indicated by, or identifiable by, a corresponding dynamic reference list index value.

[0101] In some implementations, the encoder obtains the joint dynamic reference list and the non-joint dynamic reference lists.

[0102] In a compound inter prediction mode wherein the dynamic reference list type value is the first dynamic reference list type value indicating that encoding the current block includes obtaining, such as by generating, the joint dynamic reference list for encoding the current block, the joint dynamic reference list includes one or more pairs of candidate reference motion vectors. A respective pair of candidate reference motion vectors is associated with, indicated by, or identifiable by, a corresponding dynamic reference list index value. A respective pair of candidate reference motion vectors may include a first candidate reference motion vector and a second candidate reference motion vector. A respective pair of candidate reference motion vectors is associated with, indicated by, or identifiable by, a corresponding dynamic reference list index value.

[0103] In a compound inter prediction mode wherein the dynamic reference list type value is the second dynamic reference list type value indicating that encoding the current block includes obtaining, such as by generating, two non-joint dynamic reference lists for encoding the current block, a respective non-joint dynamic reference list includes one or more candidate reference motion vectors. A first reference motion vector is associated with, indicated by, or identifiable by, a first dynamic reference list index value with respect to the first non-joint dynamic reference list. A second reference motion vector is associated with, indicated by, or identifiable by, a second dynamic reference list index value with respect to the second non-joint dynamic reference list.

[0104] In some implementations, obtaining the dynamic reference list type value (at 740) includes obtaining the dynamic reference list type value in accordance with the prediction mode (obtained at 730). Obtaining the dynamic reference list type value in accordance with the prediction mode includes determining whether a first proper subset of compound prediction modes includes the prediction mode or a second proper subset of compound prediction modes includes the prediction mode.

[0105] In some implementations, the first proper subset of compound prediction modes includes the prediction mode, and the dynamic reference list type value is identified as the first dynamic reference list type value, indicating that encoding the current block includes obtaining, such as by generating, the joint dynamic reference list for encoding the current block.

[0106] In some implementations, the second proper subset of compound prediction modes includes the prediction mode, and the dynamic reference list type value is identified as the second dynamic reference list type value, indicating that encoding the current block includes obtaining, such as by generating, two non-joint dynamic reference lists for encoding the current block.

[0107] In some implementations, the sets, or proper subsets, of compound prediction modes are defined prior to coding the current block, prior to coding the current frame, or prior to coding the current video.

[0108] In some implementations, the sets, or proper subsets, of compound prediction modes are configured at or by the encoder and corresponding information is signaled in the bitstream. In some implementations, encoding using multiple dynamic reference list types

800 includes including the data expressly indicating or configuring the sets, or proper subsets, of compound prediction modes in the encoded bitstream.

[0109] In an example, the second proper subset of compound prediction modes, associated with using the non-joint dynamic reference lists, includes the NEAR_NEARMV compound prediction mode and the NEAR_NEWMV compound prediction mode, and the first proper subset of compound prediction modes, associated with using the joint dynamic reference list, includes the compound prediction modes other than the NEAR_NEARMV compound prediction mode and the NEAR_NEWMV compound prediction mode, such as the NEW_NEARMV compound prediction mode, the GLOBAL_GLOBALMV compound prediction mode, the NEW_NEWMV compound prediction mode, the JOINT_NEWMV compound prediction mode, the JOINT_AMVDNEWMV compound prediction mode, the NEAR_NEARMV_OPTFLOW compound prediction mode, the NEAR_NEWMV_OPTFLOW compound prediction mode, the NEW_NEARMV_OPTFLOW compound prediction mode, the NEW_NEWMV_OPTFLOW compound prediction mode, the JOINT_NEWMV_OPTFLOW compound prediction mode, and the JOINT_AMVDNEWMV_OPTFLOW compound prediction mode.

[0110] In another example, the second proper subset of compound prediction modes, associated with using the non-joint dynamic reference lists, includes the NEAR_NEARMV compound prediction mode, the NEW_NEWMV compound prediction mode, and the NEW_NEWMV_OPTFLOW compound prediction mode, and the first proper subset of compound prediction modes, associated with using the joint dynamic reference list, includes the compound prediction modes other than the NEAR_NEARMV compound prediction mode, the NEW_NEWMV compound prediction mode, and the NEW_NEWMV_OPTFLOW compound prediction mode, such as the NEAR_NEWMV compound prediction mode, the NEW_NEARMV compound prediction mode, the GLOBAL_GLOBALMV compound prediction mode, the JOINT_NEWMV compound prediction mode, the JOINT_AMVDNEWMV compound prediction mode, the NEAR_NEARMV_OPTFLOW compound prediction mode, the NEAR_NEWMV_OPTFLOW compound prediction mode, the NEW_NEARMV_OPTFLOW compound prediction mode, the JOINT_NEWMV_OPTFLOW compound prediction mode, and the JOINT_AMVDNEWMV_OPTFLOW compound prediction mode.

[0111] In some implementations, obtaining the dynamic reference list type value (at 740) includes obtaining the dynamic reference list type value in accordance with a prediction block size for encoding the current block. For example, the second dynamic reference list type value indicating that encoding the current block includes obtaining, such as by generating, two non-joint dynamic reference lists for encoding the current block, may be used for prediction blocks having a size, such as a number, count, or cardinality (TV) of luma, or luminance samples, per-column, per-row, or both, that is greater than or equal to a defined, or configured, minimum block size. In another example, the first dynamic reference list type value indicating that encoding the current block includes obtaining, such as by generating, the joint dynamic reference list for encoding the current block, may be used for prediction blocks having a size, such as a number, count, or cardinality (TV) of luma, or luminance samples, per- column, per-row, or both, that is less than the defined, or configured, minimum block size. [0112] In some implementations, the minimum block size is obtained, accessed, or identified, at the encoder in the absence of data expressly indicating or configuring the minimum block size signaled in the encoded bitstream.

[0113] In some implementations, the minimum block size is obtained, accessed, or identified, at the encoder in accordance with data expressly indicating or configuring the minimum block size signaled in the encoded bitstream. In some implementations, encoding using multiple dynamic reference list types 800 includes accessing, such as by reading, encoding, extracting, or otherwise obtaining, the data expressly indicating or configuring the minimum block size signaled in the encoded bitstream.

[0114] For example, the minimum block size (TV), may be eight (TV=8), the current block, or current prediction block, may be an NxN block, such as an 8x8 block, or larger, and the second dynamic reference list type value, indicating that encoding the current block includes obtaining, such as by generating, two non-joint dynamic reference lists for encoding the current block, may be used.

[0115] In another example, the minimum block size (TV), may be sixteen (TV=16), the current block, or current prediction block, may be smaller than an NxN block, such as an 8x8 block, and the first dynamic reference list type value, indicating that encoding the current block includes obtaining, such as by generating, the joint dynamic reference list for encoding the current block, may be used.

[0116] Reference motion vectors for coding the current block are obtained (at 750) from the joint dynamic reference list or the non-joint dynamic reference lists indicated by the dynamic reference list type value (obtained at 740).

[0117] Encoded block data is obtained (at 760). Obtaining the encoded block data includes encoding the current block using the compound prediction mode (obtained at 730) using the reference motion vectors obtained (at 750) from the joint dynamic reference list or the non- joint dynamic reference lists indicated by the dynamic reference list type value (obtained at 740).

[0118] Obtaining the encoded block data includes including, in the encoded block data, data, such as one or more bits, one or more flags, one or more symbols, or one or more values, indicating the compound prediction mode for coding the current block. Obtaining the encoded block data includes including, in the encoded block data, data, such as one or more bits, one or more flags, one or more symbols, or one or more values, indicating the compound prediction mode for coding the current block.

[0119] The output, compressed, or encoded, bitstream, is output, such as stored or transmitted, such as to a decoder, (at 770).

[0120] FIG. 8 is a flowchart diagram of an example of decoding using multiple dynamic reference list types 800 in accordance with implementations of this disclosure. Decoding using multiple dynamic reference list types 800 may be implemented in a decoder, such as the decoder 500 shown in FIG. 5. Decoding using multiple dynamic reference list types 800 includes block-based hybrid video coding as described herein.

[0121] Decoding using multiple dynamic reference list types 800 includes generating reconstructed video data by decoding an encoded bitstream, such as the compressed bitstream 502 shown in FIG. 5, or one or more portions thereof, to generate a reconstructed video, or a portion thereof, such as the output video stream 504 shown in FIG. 5.

[0122] Decoding the encoded bitstream, or one or more portions thereof, for decoding using multiple dynamic reference list types 800, includes obtaining the encoded bitstream (at 810), obtaining reconstructed block data (at 820), and outputting reconstructed frame data (at 830). One or more aspects of decoding using multiple dynamic reference list types 800 may be omitted from the description herein for simplicity and brevity.

[0123] The encoded bitstream is obtained (at 810). For example, the decoder, or a component thereof, such as an intra/inter prediction unit of the decoder, such as the entropy decoding unit 510 shown in FIG. 5, may obtain the encoded bitstream. Obtaining the encoded bitstream includes identifying a current frame from a current sequence of frames to decode from the encoded bitstream to generate a current reconstructed frame.

[0124] Although not shown expressly in FIG. 8, decoding using multiple dynamic reference list types 800 includes obtaining, maintaining, or both, a decoded frame buffer. One or more of the frames in the decoded frame buffer may be reference frames, such as decoded, or reconstructed, reference frames, constructed, or alternative, reference frames, or both. The decoded frame buffer may have a defined size, such as eight (8), indicating a maximum number, count, or cardinality, of decoded frames included in, or that may be included in, the decoded frame buffer. A respective reference frame from the decoded frame buffer may be indicated, or identified, by a corresponding decoded frame buffer index value.

[0125] The reconstructed block data is obtained (at 820) for a current block of the current frame. Obtaining the reconstructed block data (at 820) includes accessing a signaled prediction mode identifier (at 822), obtaining a dynamic reference list type value (at 824), obtaining reference motion vectors (at 828), and obtaining a reconstructed block (at 828). One or more aspects of obtaining the reconstructed block data (at 820) may be omitted from the description herein for simplicity and brevity.

[0126] Accessing the signaled prediction mode identifier (at 822) for decoding the current block includes accessing the signaled prediction mode identifier from the encoded bitstream, such as by reading, obtaining, extracting, decoding, or otherwise accessing, the signaled prediction mode identifier from the encoded bitstream.

[0127] The signaled prediction mode identifier indicates a prediction mode for decoding the current block. The signaled prediction mode identifier may indicate an intra prediction mode or an inter prediction mode. For decoding using multiple dynamic reference list types 800, the signaled prediction mode identifier indicates an inter prediction mode.

[0128] In inter prediction, a motion compensated prediction (prediction block) of the current block is obtained, such as generated. The prediction block is obtained, or generated, in accordance with one or more motion vectors and one or more reference frames. To obtain a respective motion vector, the decoder obtains, such as generates, a corresponding reference motion vector. For some inter prediction modes, such as a NEAR, or NEARMV, inter prediction mode, the decoder uses the reference motion vector as the motion vector for decoding the current block. For some inter prediction modes, such as a NEW, or NEWMV, inter prediction mode, the decoder obtains, such as reads, decodes, extracts, or otherwise accesses, from the encoded bitstream, a differential motion vector and obtains, as the motion vector for decoding the current block, a combination, such as a summation (sum), of the differential motion vector and the reference motion vector.

[0129] The inter prediction mode may be a non-compound inter prediction mode or a compound inter prediction mode. In implementations of decoding using multiple dynamic reference list types 800, the signaled prediction mode identifier indicates a compound inter prediction mode.

[0130] Compound prediction, or compound inter prediction, includes obtaining predicted sample values by blending together predictions from multiple, such as two (2), reference frames, including a first reference frame and a second reference frame. In some implementations, the second reference frame may be the first reference frame. In some implementations, the second reference frame may differ from the first reference frame. In compound prediction, multiple, such as two (2), motion vectors are signaled in the encoded bitstream.

[0131] The compound inter prediction mode, or compound prediction mode, is one of one or more available compound prediction modes. The available compound prediction modes may include a defined number, count, or cardinality, of available compound prediction modes, such as thirteen (13) available compound prediction modes. For example, the available compound prediction modes may include a NEAR_NEARMV compound prediction mode, a NEAR_NEWMV compound prediction mode, a NEW_NEARMV compound prediction mode, a GLOB AL_GLOB ALM V compound prediction mode, a NEW_NEWMV compound prediction mode, a JOINT_NEWMV compound prediction mode, a JOINT_AMVDNEWMV compound prediction mode, a NEAR_NEARMV_OPTFLOW compound prediction mode, a NEAR_NEWMV_OPTFLOW compound prediction mode, a NEW_NEARMV_OPTFLOW compound prediction mode, a NEW_NEWMV_OPTFLOW compound prediction mode, a JOINT_NEWMV_OPTFLOW compound prediction mode, and a JOINT_AMVDNEWMV_OPTFLOW compound prediction mode.

[0132] The dynamic reference list type value is obtained (at 824). The dynamic reference list type value indicates whether decoding the current block includes obtaining, such as by generating, a joint dynamic reference list or two non-joint dynamic reference lists.

[0133] In some implementations, the dynamic reference list type value is obtained (at 824) in response to accessing the signaled prediction mode identifier. In some implementations, the dynamic reference list type value is accessed (at 824) in accordance with the signaled prediction mode identifier. For example, the dynamic reference list type value may be accessed (at 824) in response to determining that the signaled prediction mode identifier indicates a compound prediction mode.

[0134] A first dynamic reference list type value indicates that decoding the current block includes obtaining, such as by generating, the joint dynamic reference list for reconstructing, or decoding, the current block. In some implementations, the first dynamic reference list type value indicates that decoding the current block omits, avoids, or excludes obtaining non-joint dynamic reference lists.

[0135] A second dynamic reference list type value indicates that decoding the current block includes obtaining, such as by generating, non-joint dynamic reference lists for reconstructing, or decoding, the current block. In some implementations, the second dynamic reference list type value indicates that decoding the current block omits, avoids, or excludes obtaining the joint dynamic reference list.

[0136] In a non-compound inter prediction mode, the dynamic reference list, which is a non-joint dynamic reference list, includes one or more candidate reference motion vectors. A respective candidate reference motion vector is associated with, indicated by, or identifiable by, a corresponding dynamic reference list index value.

[0137] In a compound inter prediction mode wherein the dynamic reference list type value is the first dynamic reference list type value indicating that decoding the current block includes obtaining, such as by generating, the joint dynamic reference list for reconstructing, or decoding, the current block, the joint dynamic reference list includes one or more pairs of candidate reference motion vectors (at least one candidate reference motion vector pair). A respective pair of candidate reference motion vectors is associated with, indicated by, or identifiable by, a corresponding dynamic reference list index value. A respective pair of candidate reference motion vectors may include a first candidate reference motion vector and a second candidate reference motion vector. A respective pair of candidate reference motion vectors is associated with, indicated by, or identifiable by, a corresponding dynamic reference list index value.

[0138] In a compound inter prediction mode wherein the dynamic reference list type value is the second dynamic reference list type value indicating that decoding the current block includes obtaining, such as by generating, two non-joint dynamic reference lists for reconstructing, or decoding, the current block, a respective non-joint dynamic reference list includes one or more candidate reference motion vectors (at least one candidate reference motion vector). A first reference motion vector is associated with, indicated by, or identifiable by, a first dynamic reference list index value with respect to the first non-joint dynamic reference list. A second reference motion vector is associated with, indicated by, or identifiable by, a second dynamic reference list index value with respect to the second non- joint dynamic reference list.

[0139] In some implementations, obtaining the dynamic reference list type value (at 824) includes obtaining the dynamic reference list type value in accordance with the signaled prediction mode identifier. Obtaining the dynamic reference list type value in accordance with the signaled prediction mode identifier includes determining whether a first proper subset of compound prediction modes includes the signaled prediction mode identifier or a second proper subset of compound prediction modes includes the signaled prediction mode identifier.

[0140] In some implementations, the first proper subset of compound prediction modes includes the signaled prediction mode identifier, and the dynamic reference list type value is identified as the first dynamic reference list type value, indicating that decoding the current block includes obtaining, such as by generating, the joint dynamic reference list for reconstructing, or decoding, the current block.

[0141] In some implementations, the second proper subset of compound prediction modes includes the signaled prediction mode identifier, and the dynamic reference list type value is identified as the second dynamic reference list type value, indicating that decoding the current block includes obtaining, such as by generating, two non-joint dynamic reference lists for reconstructing, or decoding, the current block.

[0142] In some implementations, the sets, or proper subsets, of compound prediction modes are defined prior to coding the current block, prior to coding the current frame, or prior to coding the current video.

[0143] In some implementations, the sets, or proper subsets, of compound prediction modes are configured in accordance with information signaled in the bitstream. In some implementations, decoding using multiple dynamic reference list types 800 includes accessing, such as by reading, decoding, extracting, or otherwise obtaining, the data expressly indicating or configuring the sets, or proper subsets, of compound prediction modes signaled in the encoded bitstream.

[0144] In an example, the second proper subset of compound prediction modes, associated with using the non-joint dynamic reference lists, includes the NEAR_NEARMV compound prediction mode and the NEAR_NEWMV compound prediction mode, and the first proper subset of compound prediction modes, associated with using the joint dynamic reference list, includes the compound prediction modes other than the NEAR_NEARMV compound prediction mode and the NEAR_NEWMV compound prediction mode, such as the NEW_NEARMV compound prediction mode, the GLOBAL_GLOBALMV compound prediction mode, the NEW_NEWMV compound prediction mode, the JOINT_NEWMV compound prediction mode, the JOINT_AMVDNEWMV compound prediction mode, the NEAR_NEARMV_OPTFLOW compound prediction mode, the NEAR_NEWMV_OPTFLOW compound prediction mode, the

NEW_NEARMV_OPTFLOW compound prediction mode, the NEW_NEWMV_OPTFLOW compound prediction mode, the JOINT_NEWMV_OPTFLOW compound prediction mode, and the JOINT_AMVDNEWMV_OPTFLOW compound prediction mode.

[0145] In another example, the second proper subset of compound prediction modes, associated with using the non-joint dynamic reference lists, includes the NEAR_NEARMV compound prediction mode, the NEW_NEWMV compound prediction mode, and the NEW_NEWMV_OPTFLOW compound prediction mode, and the first proper subset of compound prediction modes, associated with using the joint dynamic reference list, includes the compound prediction modes other than the NEAR_NEARMV compound prediction mode, the NEW_NEWMV compound prediction mode, and the NEW_NEWMV_OPTFLOW compound prediction mode, such as the NEAR_NEWMV compound prediction mode, the NEW_NEARMV compound prediction mode, the GLOBAL_GLOBALMV compound prediction mode, the JOINT_NEWMV compound prediction mode, the JOINT_AMVDNEWMV compound prediction mode, the NEAR_NEARMV_OPTFLOW compound prediction mode, the NEAR_NEWMV_OPTFLOW compound prediction mode, the NEW_NEARMV_OPTFLOW compound prediction mode, the JOINT_NEWMV_OPTFLOW compound prediction mode, and the JOINT_AMVDNEWMV_OPTFLOW compound prediction mode.

[0146] In some implementations, obtaining the dynamic reference list type value (at 824) includes obtaining the dynamic reference list type value in accordance with a prediction block size for decoding the current block. For example, the second dynamic reference list type value indicating that decoding the current block includes obtaining, such as by generating, two non-joint dynamic reference lists for reconstructing, or decoding, the current block, may be used for prediction blocks having a size, such as a number, count, or cardinality ( of luma, or luminance samples, per-column, per-row, or both, that is greater than or equal to a defined, or configured, minimum block size. In another example, the first dynamic reference list type value indicating that decoding the current block includes obtaining, such as by generating, the joint dynamic reference list for reconstructing, or decoding, the current block, may be used for prediction blocks having a size, such as a number, count, or cardinality (A of luma, or luminance samples, per-column, per-row, or both, that is less than the defined, or configured, minimum block size.

[0147] In some implementations, the minimum block size is obtained, accessed, or identified, at the decoder in the absence of data expressly indicating or configuring the minimum block size signaled in the encoded bitstream.

[0148] In some implementations, the minimum block size is obtained, accessed, or identified, at the decoder in accordance with data expressly indicating or configuring the minimum block size signaled in the encoded bitstream. In some implementations, decoding using multiple dynamic reference list types 800 includes accessing, such as by reading, decoding, extracting, or otherwise obtaining, the data expressly indicating or configuring the minimum block size signaled in the encoded bitstream.

[0149] For example, the minimum block size (TV), may be eight (TV=8), the current block, or current prediction block, may be an NxN block, such as an 8x8 block, or larger, and the second dynamic reference list type value, indicating that decoding the current block includes obtaining, such as by generating, two non-joint dynamic reference lists for reconstructing, or decoding, the current block, may be used.

[0150] In another example, the minimum block size (TV), may be sixteen (TV= 16), the current block, or current prediction block, may be smaller than an NxN block, such as an 8x8 block, and the first dynamic reference list type value, indicating that decoding the current block includes obtaining, such as by generating, the joint dynamic reference list for reconstructing, or decoding, the current block, may be used.

[0151] Obtaining reference motion vectors (at 828) includes obtaining, such as by generating, one or more dynamic reference lists in accordance with the dynamic reference list type value. A respective dynamic reference list may have a defined size, indicating a defined number, count, or cardinality, such as three (3) or four (4), of candidate reference motion vectors, or candidate reference motion vector pairs included in the respective dynamic reference list.

[0152] In some implementations, the dynamic reference list type value is the first dynamic reference list type value indicating that decoding the current block includes obtaining, such as by generating, the joint dynamic reference list for reconstructing, or decoding, the current block, and generating the one or more dynamic reference lists in accordance with the dynamic reference list type value includes generating the joint dynamic reference list.

[0153] In some implementations, the dynamic reference list type value is the second dynamic reference list type value indicating that decoding the current block includes obtaining, such as by generating, the two non-joint dynamic reference lists for reconstructing, or decoding, the current block, and generating the one or more dynamic reference lists in accordance with the dynamic reference list type value includes generating the two non-joint dynamic reference lists.

[0154] In some implementations, the dynamic reference list type value is the second dynamic reference list type value indicating that decoding the current block includes obtaining, such as by generating, the two non-joint dynamic reference lists for reconstructing, or decoding, the current block, the compound prediction mode is the NEAR_NEARMV compound prediction mode, and the defined size of the respective non-joint dynamic reference lists is four (4).

[0155] In some implementations, the dynamic reference list type value is the second dynamic reference list type value indicating that decoding the current block includes obtaining, such as by generating, the two non-joint dynamic reference lists for reconstructing, or decoding, the current block, the compound prediction mode is the NEAR_NEWMV compound prediction mode, and the defined size of the respective non-joint dynamic reference lists is three (3).

[0156] Generating, or otherwise obtaining, a respective dynamic reference list includes obtaining one or more candidate reference motion vectors from one or more context blocks, such as previously decoded, or reconstructed, blocks neighboring, or immediately adjacent to, the current block, such as above the current block, to the left of the current block, or above and to the left of the current block, or otherwise preceding the current block in a block coding order or sequence used for coding the current frame, or in a collocated block from a reference frame, at a location equivalent to, concurrent with, or corresponding to, a location of the current block in the current frame, wherein the candidate reference motion vector was, or candidate reference motion vectors were, used as motion vectors for obtaining, such as by generating, the respective decoded, or reconstructed, block.

[0157] Obtaining reference motion vectors (at 828) includes accessing, such as by decoding, from the encoded bitstream, one or more signaled dynamic reference list index values.

[0158] In some implementations, the dynamic reference list type value is the first dynamic reference list type value indicating that decoding the current block includes obtaining, such as by generating, the joint dynamic reference list for reconstructing, or decoding, the current block, and accessing, such as by decoding, from the encoded bitstream, one or more signaled dynamic reference list index values, includes accessing, such as by decoding, from the encoded bitstream, a signaled joint dynamic reference list index value with respect to the joint dynamic reference list.

[0159] In response to determining that the dynamic reference list type value is the first dynamic reference list type value, the decoder obtains, such as generates, the joint dynamic reference list, accesses, such as decodes, the signaled joint dynamic reference list index value with respect to the joint dynamic reference list, and accesses a pair of candidate reference motion vectors from the joint dynamic reference list in accordance with the signaled joint dynamic reference list index value, wherein the pair of candidate reference motion vectors includes a first candidate reference motion vector, used as the first reference motion vector, and a second candidate reference motion vector, used as the second reference motion vector. [0160] In some implementations, the dynamic reference list type value is the second dynamic reference list type value indicating that decoding the current block includes obtaining, such as by generating, the two non-joint dynamic reference lists for reconstructing, or decoding, the current block, and accessing, such as by decoding, from the encoded bitstream, one or more signaled dynamic reference list index values, includes accessing, such as by decoding, from the encoded bitstream, a first signaled non-joint dynamic reference list index value with respect to the first non-joint dynamic reference list, and a second signaled non-joint dynamic reference list index value with respect to the second non-joint dynamic reference list.

[0161] In response to determining that the dynamic reference list type value is the second dynamic reference list type value, the decoder obtains, such as generates, the first non-joint dynamic reference list and the second non-joint dynamic reference list, accesses, such as decodes, the first signaled non-joint dynamic reference list index value with respect to the first non-joint dynamic reference list, obtains, from the first non-joint dynamic reference list, as the first reference motion vector, a first candidate reference motion vector indicated by the first signaled non-joint dynamic reference list index value, accesses, such as decodes, the second signaled non-joint dynamic reference list index value with respect to the second non- joint dynamic reference list, and obtains, from the second non-joint dynamic reference list, as the second reference motion vector, a second candidate reference motion vector indicated by the second signaled non-joint dynamic reference list index value. In some implementations, the second signaled non-joint dynamic reference list index value may be signaled differentially with respect to the first signaled non-joint dynamic reference list index value. [0162] Obtaining the reconstructed current block (at 828) includes reconstructing the current block using the first reference motion vector and the second reference motion vector. [0163] Reconstructing the current block using the first reference motion vector and the second reference motion vector includes obtaining, such as by generating, a first prediction block in accordance with the first reference motion vector. In some implementations, the compound prediction mode is the NEAR_NEARMV compound prediction mode or the NEAR_NEWMV compound prediction mode and obtaining the first prediction block in accordance with the first reference motion vector includes using the first reference motion vector as a first motion vector for obtaining the first prediction block.

[0164] Reconstructing the current block using the first reference motion vector and the second reference motion vector includes obtaining, such as by generating, a second prediction block in accordance with the second reference motion vector. In some implementations, the compound prediction mode is the NEAR_NEARMV compound prediction mode and obtaining the second prediction block in accordance with the second reference motion vector includes using the second reference motion vector as a second motion vector for obtaining the second prediction block. In some implementations, the compound prediction mode is the NEAR_NEWMV compound prediction mode and obtaining the second prediction block in accordance with the second reference motion vector includes obtaining, such as reading, decoding, extracting, or otherwise accessing, from the encoded bitstream, a differential motion vector, and obtaining, as the second motion vector for obtaining the second prediction block, a combination, such as a summation (sum), of the differential motion vector and the second reference motion vector.

[0165] Reconstructing the current block includes obtaining, such as by generating, a reconstructed current block using the first prediction block and the second prediction block, such as by combining, such as by summing or averaging, which may be weighted averaging, the first prediction block with the second prediction block.

[0166] The decoder outputs the reconstructed frame data for the current frame (at 830). Outputting the reconstructed frame data for the current frame includes including the reconstructed current block in the reconstructed frame data for the reconstructed frame.

[0167] As used herein, the terms “optimal”, “optimized”, “optimization”, or other forms thereof, are relative to a respective context and are not indicative of absolute theoretic optimization unless expressly specified herein.

[0168] As used herein, the term “set” indicates a distinguishable collection or grouping of zero or more distinct elements or members that may be represented as a one-dimensional array or vector, except as expressly described herein or otherwise clear from context.

[0169] The words “example” or “exemplary” are used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “example” or “exemplary” not necessarily to be construed as preferred or advantageous over other aspects or designs. Rather, use of the words “example” or “exemplary” is intended to present concepts in a concrete fashion. As used in this application, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or”. That is, unless specified otherwise, or clear from context, “X includes A or B” is intended to mean any of the natural inclusive permutations. That is, if X includes A; X includes B; or X includes both A and B, then “X includes A or B” is satisfied under any of the foregoing instances. In addition, the articles “a” and “an” as used in this application and the appended claims should generally be construed to mean “one or more” unless specified otherwise or clear from context to be directed to a singular form. Moreover, use of the term “an embodiment” or “one embodiment” or “an implementation” or “one implementation” throughout is not intended to mean the same embodiment or implementation unless described as such. As used herein, the terms “determine” and “identify”, or any variations thereof, includes selecting, ascertaining, computing, looking up, receiving, determining, establishing, obtaining, or otherwise identifying or determining in any manner whatsoever using one or more of the devices shown in FIG. 1.

[0170] Further, for simplicity of explanation, although the figures and descriptions herein may include sequences or series of steps or stages, elements of the methods disclosed herein can occur in various orders and/or concurrently. Additionally, elements of the methods disclosed herein may occur with other elements not explicitly presented and described herein. Furthermore, one or more elements of the methods described herein may be omitted from implementations of methods in accordance with the disclosed subject matter.

[0171] The implementations of the transmitting computing and communication device 100A and/or the receiving computing and communication device 100B (and the algorithms, methods, instructions, etc. stored thereon and/or executed thereby) can be realized in hardware, software, or any combination thereof. The hardware can include, for example, computers, intellectual property (IP) cores, application- specific integrated circuits (ASICs), programmable logic arrays, optical processors, programmable logic controllers, microcode, microcontrollers, servers, microprocessors, digital signal processors or any other suitable circuit. In the claims, the term “processor” should be understood as encompassing any of the foregoing hardware, either singly or in combination. The terms “signal” and “data” are used interchangeably. Further, portions of the transmitting computing and communication device 100A and the receiving computing and communication device 100B do not necessarily have to be implemented in the same manner.

[0172] Further, in one implementation, for example, the transmitting computing and communication device 100A or the receiving computing and communication device 100B can be implemented using a computer program that, when executed, carries out any of the respective methods, algorithms and/or instructions described herein. In addition, or alternatively, for example, a special purpose computer/processor can be utilized which can contain specialized hardware for carrying out any of the methods, algorithms, or instructions described herein.

[0173] The transmitting computing and communication device 100A and receiving computing and communication device 100B can, for example, be implemented on computers in a real-time video system. Alternatively, the transmitting computing and communication device 100A can be implemented on a server and the receiving computing and communication device 100B can be implemented on a device separate from the server, such as a hand-held communications device. In this instance, the transmitting computing and communication device 100A can encode content using an encoder 400 into an encoded video signal and transmit the encoded video signal to the communications device. In turn, the communications device can then decode the encoded video signal using a decoder 500. Alternatively, the communications device can decode content stored locally on the communications device, for example, content that was not transmitted by the transmitting computing and communication device 100A. Other suitable transmitting computing and communication device 100A and receiving computing and communication device 100B implementation schemes are available. For example, the receiving computing and communication device 100B can be a generally stationary personal computer rather than a portable communications device and/or a device including an encoder 400 may also include a decoder 500.

[0174] Further, all or a portion of implementations can take the form of a computer program product accessible from, for example, a tangible computer-usable or computer- readable medium. A computer-usable or computer-readable medium can be any device that can, for example, tangibly contain, store, communicate, or transport the program for use by or in connection with any processor. The medium can be, for example, an electronic, magnetic, optical, electromagnetic, or a semiconductor device. Other suitable mediums are also available.

[0175] It will be appreciated that aspects can be implemented in any convenient form. For example, aspects may be implemented by appropriate computer programs which may be carried on appropriate carrier media which may be tangible carrier media (e.g., disks) or intangible carrier media (e.g. communications signals). Aspects may also be implemented using suitable apparatus which may take the form of programmable computers running computer programs arranged to implement the methods and/or techniques disclosed herein. Aspects can be combined such that features described in the context of one aspect may be implemented in another aspect. [0176] The above-described implementations have been described in order to allow easy understanding of the application are not limiting. On the contrary, the application covers various modifications and equivalent arrangements included within the scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structure as is permitted under the law.

Claims

CLAIMS What is claimed is:

1. A method comprising: generating reconstructed video data by decoding an encoded bitstream, wherein decoding the encoded bitstream includes: obtaining reconstructed block data for a current block of a current frame of a sequence of frames, wherein obtaining the reconstructed block data includes: accessing, from the encoded bitstream, a signaled prediction mode identifier for decoding the current block, wherein the signaled prediction mode identifier indicates a compound prediction mode; in response to accessing the signaled prediction mode identifier, obtaining a dynamic reference list type value; obtaining, in accordance with the dynamic reference list type value, a first reference motion vector and a second reference motion vector; obtaining a reconstructed current block by reconstructing the current block using the first reference motion vector and the second reference motion vector; and including the reconstructed current block in the reconstructed block data; including the reconstructed block data in reconstructed frame data for the current frame; including the reconstructed frame data in the reconstructed video data; and outputting the reconstructed video data.

2. The method of claim 1, wherein obtaining the dynamic reference list type value includes: identifying a proper subset of compound prediction modes that includes the compound prediction mode; and identifying the dynamic reference list type value in accordance with the proper subset of compound prediction modes.

3. The method of claim 2, wherein: identifying the proper subset of compound prediction modes includes: determining whether a first proper subset of compound prediction modes includes the compound prediction mode; and in response to determining that the first proper subset of compound prediction modes includes the compound prediction mode, identifying the first proper subset of compound prediction modes as the proper subset of compound prediction modes; and identifying the dynamic reference list type value in accordance with the proper subset of compound prediction modes includes: in response to determining that the first proper subset of compound prediction modes includes the compound prediction mode, identifying, as the dynamic reference list type value, a first dynamic reference list type value, indicating that decoding the current block includes obtaining a joint dynamic reference list for decoding the current block, wherein the joint dynamic reference list includes at least one pair of candidate reference motion vectors.

4. The method of claim 2, wherein: identifying the proper subset of compound prediction modes includes: determining whether a second proper subset of compound prediction modes includes the compound prediction mode; and in response to determining that the second proper subset of compound prediction modes includes the compound prediction mode, identifying the second proper subset of compound prediction modes as the proper subset of compound prediction modes; and identifying the dynamic reference list type value in accordance with the proper subset of compound prediction modes includes: in response to determining that the second proper subset of compound prediction modes includes the compound prediction mode, identifying, as the dynamic reference list type value, a second dynamic reference list type value, indicating that decoding the current block includes obtaining two non-joint dynamic reference lists for decoding the current block, wherein a respective non-joint dynamic reference list includes at least one candidate reference motion vector.

5. The method of claim 4, wherein obtaining the reconstructed block data includes: accessing, from the encoded bitstream, data indicating which compound prediction modes are included in the second proper subset of compound prediction modes.

6. The method of claim 4, wherein the second proper subset of compound prediction modes includes a NEAR_NEARMV compound prediction mode and a NEAR_NEWMV compound prediction mode.

7. The method of claim 4, wherein the compound prediction mode is a NEAR_NEARMV compound prediction mode and a defined size of the respective non-joint dynamic reference lists is four.

8. The method of claim 4, wherein the compound prediction mode is a NEAR_NEWMV compound prediction mode and a defined size of the respective non-joint dynamic reference lists is three.

9. The method of claim 4, wherein obtaining the first reference motion vector and the second reference motion vector includes: accessing, from the encoded bitstream, a first signaled non-joint dynamic reference list index value with respect to a first non-joint dynamic reference list; obtaining, from the first non-joint dynamic reference list, as the first reference motion vector, a first candidate reference motion vector indicated by the first signaled non-joint dynamic reference list index value; accessing, from the encoded bitstream, a second signaled non-joint dynamic reference list index value with respect to a second non-joint dynamic reference list; and obtaining, from the second non-joint dynamic reference list, as the second reference motion vector, a second candidate reference motion vector indicated by the second signaled non-joint dynamic reference list index value.

10. A non-transitory computer-readable storage medium storing an encoded bitstream comprising: encoded block data for a current block of a current frame of a sequence of frames; data indicating a prediction mode identifier, wherein the prediction mode identifier indicates a compound prediction mode that includes using a first non-joint dynamic reference list and a second non-joint dynamic reference list to obtain motion vectors for obtaining reconstructed block data corresponding to the encoded block data; data indicating a first non-joint dynamic reference list index value with respect to the first non-joint dynamic reference list; and data indicating a second non-joint dynamic reference list index value with respect to the second non-joint dynamic reference list.

11. The non-transitory computer-readable storage medium storing of claim 10, wherein the encoded bitstream includes: data indicating which compound prediction modes are included a proper subset of compound prediction modes.

12. A method comprising: obtaining an encoded bitstream by encoding a current block of a current frame of a sequence of frames, wherein encoding the current block includes: obtaining a prediction mode identifier indicating a prediction mode for encoding the current block, wherein the prediction mode is a compound prediction mode; obtaining a first motion vector for encoding the current block with reference to a first reference frame; obtaining a second motion vector for encoding the current block with reference to a second reference frame; obtaining a dynamic reference list type value; obtaining, in accordance with the dynamic reference list type value, a first reference motion vector and a second reference motion vector; encoding the first motion vector in accordance with the first reference motion vector; encoding the second motion vector in accordance with the second reference motion vector; and including data indicating the prediction mode identifier in the encoded bitstream; and outputting the encoded bitstream.

13. The method of claim 12, wherein obtaining the dynamic reference list type value includes: identifying a proper subset of compound prediction modes that includes the compound prediction mode; and identifying the dynamic reference list type value in accordance with the proper subset of compound prediction modes.

14. The method of claim 13, wherein: identifying the proper subset of compound prediction modes includes: determining whether a first proper subset of compound prediction modes includes the compound prediction mode; and in response to determining that the first proper subset of compound prediction modes includes the compound prediction mode, identifying the first proper subset of compound prediction modes as the proper subset of compound prediction modes; and identifying the dynamic reference list type value in accordance with the proper subset of compound prediction modes includes: in response to determining that the first proper subset of compound prediction modes includes the compound prediction mode, identifying, as the dynamic reference list type value, a first dynamic reference list type value, indicating that encoding the current block includes obtaining a joint dynamic reference list for encoding the current block, wherein the joint dynamic reference list includes at least one pair of candidate reference motion vectors.

15. The method of claim 13, wherein: identifying the proper subset of compound prediction modes includes: determining whether a second proper subset of compound prediction modes includes the compound prediction mode; and in response to determining that the second proper subset of compound prediction modes includes the compound prediction mode, identifying the second proper subset of compound prediction modes as the proper subset of compound prediction modes; and identifying the dynamic reference list type value in accordance with the proper subset of compound prediction modes includes: in response to determining that the second proper subset of compound prediction modes includes the compound prediction mode, identifying, as the dynamic reference list type value, a second dynamic reference list type value, indicating that encoding the current block includes obtaining two non-joint dynamic reference lists for encoding the current block, wherein a respective non-joint dynamic reference list includes at least one candidate reference motion vector.

16. The method of claim 15, wherein encoding the current block includes: including, in the encoded bitstream, data indicating which compound prediction modes are included in the second proper subset of compound prediction modes.

17. The method of claim 15, wherein the second proper subset of compound prediction modes includes a NEAR_NEARMV compound prediction mode and a NEAR_NEWMV compound prediction mode.

18. The method of claim 15, wherein the compound prediction mode is a NEAR_NEARMV compound prediction mode and a defined size of the respective non-joint dynamic reference lists is four.

19. The method of claim 15, wherein the compound prediction mode is a NEAR_NEWMV compound prediction mode and a defined size of the respective non-joint dynamic reference lists is three.

20. The method of claim 15, wherein obtaining the first reference motion vector and the second reference motion vector includes: obtaining, from a first non-joint dynamic reference list, as the first reference motion vector, a first candidate reference motion vector indicated by a first non-joint dynamic reference list index value with respect to the first non-joint dynamic reference list; including, in the encoded bitstream, data indicating the first non-joint dynamic reference list index value; obtaining, from a second non-joint dynamic reference list, as the second reference motion vector, a second candidate reference motion vector indicated by a second non-joint dynamic reference list index value with respect to the second non-joint dynamic reference list; and including, in the encoded bitstream, data indicating the second non-joint dynamic reference list index value.