JP7210658B2 - Audio processing unit and method of decoding encoded audio bitstream - Google Patents

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application claims priority from European Patent Application No. 15159067.6 filed March 13, 2015 and US Provisional Application No. 62/133,800 filed March 16, 2016 is. The contents of each document are incorporated by reference in their entirety.
TECHNICAL FIELD The present invention relates to audio signal processing. Some embodiments relate to encoding and decoding audio bitstreams (eg, bitstreams with MPEG-4 AAC format). Other embodiments relate to decoding of such bitstreams by legacy decoders not configured to perform eSBR processing and ignoring such metadata, or to decoding audio streams that do not include such metadata. For bitstream decoding, it includes by generating eSBR control data in response to the bitstream.

A typical audio bitstream represents audio data (e.g., encoded audio data) indicative of one or more channels of audio content and at least one characteristic of said audio data or audio content. including both metadata and One well-known format for generating encoded audio bitstreams is the MPEG-4 Advanced Audio Coding (AAC) format described in MPEG standard ISO/IEC14496-3:2009. be. In the MPEG-4 standard, AAC stands for "advanced audio coding" and HE-AAC stands for "high-efficiency advanced audio coding".

The MPEG-4 AAC standard defines several audio profiles that determine which objects and coding tools are present in a conforming encoder or decoder. Three of these audio profiles are (1) AAC profile, (2) HE-AAC profile and (3) HE-AAC v2 profile. The AAC profile includes AAC low complexity (or "AAC-LC") object types. The AAC-LC object type corresponds to the MPEG-2 AAC low-complexity profile with some adjustments, and the spectral band replication ("SBR") object type also supports parametric stereo. ) ("PS") object type. The HE-AAC profile is a superset of the AAC profile and additionally contains the SBR object type. The HE-AAC v2 profile is a superset of the HE-AAC profile and additionally contains the PS object type.

The SBR object type contains spectral band replication tools. It is an important coding tool that significantly improves the compression efficiency of perceptual audio codecs. SBR reconstructs the high frequency components of the audio signal at the receiver side (eg at the decoder). As such, the encoder need only encode and transmit the low frequency components, allowing much higher audio quality at low data rates. SBR is based on duplicating a previously truncated sequence of harmonics to reduce the data rate from the available bandwidth limited signal and control data obtained from the encoder. The ratio between tone-like and noise-like components is maintained by adaptive inverse filtering and optional addition of noise and sinusoids. In the MPEG-4 AAC standard, the SBR tool copies several adjacent quadrature mirror filter (QMF) subbands from the transmitted lowband portion of the audio signal to the highband portion of the audio signal generated at the decoder. Performs spectral patching.

MPEG standardISO/IEC14496-3:2009

Spectral patching may not be ideal for certain audio types, such as musical content with relatively low crossover frequencies. Therefore, techniques are needed to improve spectral band duplication.

A first class of embodiments relates to an audio processing unit that includes a memory, a bitstream payload deformatter, and a decoding subsystem. The memory is configured to store at least one block of an encoded audio bitstream (eg MPEG-4 AAC bitstream). A bitstream payload de-formatter is configured to demultiplex the encoded audio blocks. A decoding subsystem is configured to decode the audio content of the encoded audio blocks. An encoded audio block contains a fill element. A filler element has an identifier indicating the beginning of the filler element and filler data after the identifier. The fill data includes at least one flag identifying whether enhanced spectral band replication (eSBR) processing should be performed on the audio content of the encoded audio block.

A second class of embodiments relates to a method for decoding an encoded audio bitstream. The method includes receiving at least one block of an encoded audio bitstream, demultiplexing at least some portions of the at least one block of the encoded audio bitstream, and decoding the encoded audio bitstream. • decoding at least some portions of said at least one block of the bitstream; The at least one block of the encoded audio bitstream includes a fill element. A filler element has an identifier indicating the beginning of the filler element and filler data after the identifier. The filling data at least one identifying whether enhanced spectral band replication (eSBR) processing should be performed on the audio content of the at least one block of the encoded audio bitstream. contains two flags.

Another class of embodiments relates to encoding and transcoding audio bitstreams that include metadata identifying whether enhanced spectral band replication (eSBR) processing should be performed.

1 is a block diagram of an embodiment of a system that may be configured to carry out certain embodiments of the method of the present invention; FIG. 1 is a block diagram of an encoder that is an embodiment of an audio processing unit of the invention; FIG. 1 is a block diagram of a system including a decoder, which is an embodiment of an audio processing unit of the invention, and optionally also a post-processor coupled thereto; FIG. 1 is a block diagram of a decoder, which is an embodiment of an audio processing unit of the invention; FIG. FIG. 4 is a block diagram of a decoder, another embodiment of the audio processing unit of the present invention; FIG. 4 is a block diagram of another embodiment of the audio processing unit of the present invention; Fig. 3 shows a block of an MPEG-4 AAC bitstream containing segmented segments;

Throughout this disclosure, including the claims, references to performing an operation "on" a signal or data (e.g., filtering, scaling, transforming, or applying a gain to the signal or data) include perform the operation directly or on a processed version of the signal or data (e.g., on a version of the signal that has undergone preliminary filtering or preprocessing prior to performing the operation) used broadly to mean

Throughout this disclosure, including the claims, the expression "audio processing unit" is used broadly to denote a system, device or apparatus configured to process audio data. Examples of audio processing units include, but are not limited to, encoders (eg, transcoders), decoders, codecs, pre-processing systems, post-processing systems and bitstream processing systems (sometimes referred to as bitstream processing tools). Virtually every consumer electronic device such as mobile phones, televisions, laptops and tablet computers includes an audio processing unit.

Throughout this disclosure, including the claims, the terms "coupled" or "coupled" are used broadly to mean a direct or indirect connection. Thus, when a first device couples to a second device, the connection may be through a direct connection or through an indirect connection through other devices and connections. In addition, components integrated within or with other components are also coupled together.

<Detailed description of embodiments of the present invention>
The MPEG-4 AAC standard specifies that an encoded MPEG-4 AAC bitstream should be subjected to SBR processing (if any) to be applied by decoders to decode the audio content of the bitstream. Metadata indicating respective types and/or indicating at least one characteristic or parameter of at least one SBR tool to be used to control such SBR processing and/or to decode the audio content of the bitstream. I'm thinking of including Here we use the expression "SBR metadata" to denote this type of metadata described or referred to in the MPEG-4 AAC standard.

The top level of an MPEG-4 AAC bitstream is a sequence of data blocks ("raw_data_block" elements), each data block containing audio data (typically spanning a time period of 1024 or 960 samples) and associated A segment of data (referred to herein as a block) that contains information and/or other data. where one (but not more than two) "raw_data_block" elements of an MPEG-4 AAC bitstream containing audio data (and corresponding metadata and optionally other related data) are determined or indicated We use the term "block" to represent a segment.

Each block of an MPEG-4 AAC bitstream can contain several syntax elements (each of which is also embodied as a segment of data in the bitstream). Seven types of such syntax elements are defined in the MPEG-4 AAC standard. Each syntax element is identified by a different value of the data element "id_syn_ele". Examples of syntax elements include "single_channel_element()", "channel_pair_element()" and "fill_element()". A single channel element is a container containing the audio data of a single audio channel (a monophonic audio signal). A channel pair element contains audio data for two audio channels (ie, a stereo audio signal).

A fill element is a container of information that includes an identifier (eg, the value of the element "id_syn_ele" above) and subsequent data called "fill data". Filling factors have historically been used to adjust the instantaneous bitrate of a bitstream to be transmitted over a constant rate channel. A constant data rate can be achieved by adding an appropriate amount of padding data to each block.

According to embodiments of the invention, the filler data may include one or more extension payloads that extend the types of data (eg, metadata) that can be transmitted in the bitstream. A decoder that receives a bitstream with fill data containing new types of data may optionally be used by a device (eg, a decoder) that receives the bitstream to extend the functionality of the device. Thus, as those skilled in the art will appreciate, a filler element is a special type of data structure that is typically used to carry audio data (e.g., an audio payload containing channel data). Different from structure.

In some embodiments of the present invention, identifiers used to identify filler elements are three-bit unsigned integers with a value of 0x6, most significant transmitted most significant bit first. bit first) ("uimsbf"). Several instances of the same type of syntax element (eg several filler elements) may occur in one block.

Another standard for encoding audio bitstreams is the MPEG Unified Speech and Audio Coding (USAC) standard (ISO/IEC 23003-3:2012). The MPEG USAC standard encodes and decodes audio content using spectral band replication processing (including SBR processing described in the MPEG-4 AAC standard, as well as other enhanced forms of spectral band replication processing). It describes that This process is an extended and enhanced version of the spectral band replication tool (sometimes referred to herein as the "enhanced SBR tool" or "eSBR tool") of the set of SBR tools described in the MPEG-4 AAC standard. ) apply. Thus, eSBR (defined in the USAC standard) is an improvement over SBR (defined in the MPEG-4 AAC standard).

In this document, the term "enhanced SBR processing" (or "eSBR processing") refers to at least one eSBR tool not described or mentioned in the MPEG-4 AAC (e.g. MPEG USAC standard). used to represent a spectral band duplication process that uses at least one eSBR tool (provided). Examples of such eSBR tools are harmonic transposition, QMF patching additional preprocessing or "pre-flattening" and subband-to-sample temporal envelope shaping or " Inter TES”.

A bitstream generated according to the MPEG USAC standard (sometimes referred to herein as a USAC bitstream) contains encoded audio content, and typically a decoding method is used to decode the audio content of the USAC bitstream. Metadata indicating each type of spectral band replication processing to be applied by a decoder and/or to be used to control such spectral band replication processing and/or to decode audio content of said USAC bitstream. Metadata indicative of at least one characteristic or parameter of at least one SBR tool and/or eSBR tool.

Here, the expression "enhanced SBR metadata" (or "eSBR metadata") refers to the spectrum to be applied by a decoder to decode the audio content of an encoded audio bitstream (e.g. USAC bitstream). of at least one SBR tool and/or eSBR tool to be used to indicate respective types of band duplicating processes and/or control such spectral band duplicating processes and/or decode such audio content; Used to represent metadata indicating at least one property or parameter that is not described or mentioned in the MPEG-4 AAC standard. An example of eSBR metadata is metadata (to indicate or control the spectral band duplication process) that is described or mentioned in the MPEG USAC standard but not described or mentioned in the MPEG-4 AAC standard. Thus, eSBR metadata in this document refers to metadata that is not SBR metadata, and SBR metadata in this document refers to metadata that is not eSBR metadata.

A USAC bitstream may contain both SBR metadata and eSBR metadata. More specifically, the USAC bitstream may include eSBR metadata that controls performance of eSBR processing by the decoder and SBR metadata that controls performance of SBR processing by the decoder. According to an exemplary embodiment of the invention, eSBR metadata (e.g. eSBR-specific configuration data) is (according to the invention) embedded in the MPEG-4 AAC bitstream (e.g. in the sbr_extension() container at the end of the SBR payload). be included.

During decoding of an encoded bitstream using an eSBR toolset (which includes at least one eSBR tool), the performance of eSBR processing by the decoder is based on replicating the sequence of harmonics truncated during encoding. Regenerate the high frequency range of the audio signal. Such eSBR processing typically adjusts the spectral envelope of the generated high frequency band, applies inverse filtering, and removes noise and sinusoidal components to reproduce the spectral characteristics of the original audio signal. Add.

According to exemplary embodiments of the present invention, the eSBR metadata (e.g. a few control bits that are eSBR metadata) is the metadata of an encoded audio bitstream (e.g. an MPEG-4 AAC bitstream). Included in one or more of the segments. The encoded audio bitstream also contains encoded audio data in other segments (audio data segments). Typically, at least one such metadata segment of each block of the bitstream is (or contains) a filler element (including an identifier indicating the beginning of the filler element), and the eSBR metadata is It is included in the filler element after the identifier.

FIG. 1 is a block diagram of an exemplary audio processing chain (audio data processing system), one or more of the elements of which may be configured in accordance with embodiments of the present invention. The system includes the following elements coupled together as shown: encoder 1, delivery subsystem 2, decoder 3 and post-processing unit 4. In variations of the illustrated system, one or more of the elements are omitted or additional audio data processing units are included.

In some implementations, encoder 1 (which optionally includes a pre-processing unit) accepts as input PCM (time domain) samples containing audio content and encoded audio files representing the audio content. It is configured to output a bitstream (with a format compliant with the MPEG-4 AAC standard). Bitstream data representing audio content is sometimes referred to herein as "audio data" or "encoded audio data." When the encoder is configured according to the exemplary embodiment of the present invention, the audio bitstream output from the encoder contains eSBR metadata (and typically other metadata as well) in addition to the audio data.

One or more encoded audio bitstreams output from encoder 1 may be presented to encoded audio delivery subsystem 2 . Subsystem 2 is configured to store and/or deliver each encoded bitstream output from encoder 1 . The encoded audio bitstream output from encoder 1 may be stored by subsystem 2 (eg in the form of a DVD or Blu-ray disc) or may be stored by subsystem 2 (which may implement a transmission link or network). ), or may be stored and transmitted by subsystem 2.

Decoder 3 is configured to decode the encoded MPEG-4 AAC audio bitstream (produced by encoder 1) received via subsystem 2; In some embodiments, decoder 3 extracts eSBR metadata from each block of the bitstream, decodes the bitstream (including by performing eSBR processing using the extracted eSBR metadata ), configured to generate decoded audio data (eg, a stream of decoded PCM audio samples). In some embodiments, decoder 3 extracts SBR metadata from the bitstream (but ignores eSBR metadata included in the bitstream) and decodes the bitstream (using the extracted SBR metadata). (including by performing SBR processing on the device) to generate decoded audio data (eg, a stream of decoded PCM audio samples). Decoder 3 typically includes a buffer that stores (eg, in a non-transitory manner) segments of the encoded audio bitstream received from subsystem 2 .

Post-processing unit 4 of FIG. 1 is configured to accept a stream of decoded audio data (eg, decoded PCM audio samples) from decoder 3 and perform post-processing thereon. The post-processing unit may be configured to render post-processed audio content (or decoded audio received from decoder 3) for playback by one or more speakers.

FIG. 2 is a block diagram of an encoder (100), one embodiment of the audio processing unit of the present invention. Any of the components or elements of encoder 100 may be implemented in hardware, software, or a combination of hardware and software, as one or more processes and/or one or more circuits (e.g., ASICs, FPGAs, or other integrated circuits). , may be implemented. Encoder 100 comprises encoder 105, stuffer/formatter stage 107, metadata generation stage 106 and buffer memory 109, connected as shown. Typically, encoder 100 also includes other processing elements (not shown). Encoder 100 is configured to convert an input audio bitstream into an encoded output MPEG-4 AAC bitstream.

Metadata generator 106 generates metadata (including eSBR metadata and SBR metadata) to be included by stage 107 in the encoded bitstream to be output from encoder 100 (and/or passes through stage 107). combined and configured in such a way that

Encoder 105 encodes the input audio data (eg, by performing compression on it) and the resulting encoded audio for inclusion in the encoded bitstream to be output from stage 107. , are coupled and configured to present on stage 107 .

Stage 107 multiplexes the encoded audio from encoder 105 and the metadata from generator 106 (including eSBR metadata and SBR metadata) to produce an encoded bitstream to be output from stage 107. configured to Preferably, the encoded bitstream has a format defined by one of the embodiments of the invention.

Buffer memory 109 is configured to store (eg, in a non-transitory manner) at least one block of the encoded audio bitstream output from stage 107 . The sequence of blocks of encoded audio bitstream is then presented from buffer memory 109 as output from encoder 100 to the delivery system.

FIG. 3 is a block diagram of a system including a decoder (200), which is an embodiment of the audio processing unit of the invention, and optionally also a post-processor (300) coupled thereto. Any of the components or elements of decoder 200 may be implemented in hardware, software, or a combination of hardware and software, as one or more processes and/or one or more circuits (e.g., ASICs, FPGAs, or other integrated circuits). , may be implemented. Decoder 200 includes a buffer memory 201, a bitstream payload deformatter (parser) 205, an audio decoding subsystem 202 (sometimes a "core" decoding stage or "core" decoding stage), connected as shown. subsystem), an eSBR processing stage 203 and a control bit generation stage 204 . Typically, decoder 200 also includes other processing elements (not shown).

A buffer memory (buffer) 201 stores (eg, in a non-transitory manner) at least one block of an encoded MPEG-4 AAC audio bitstream received by decoder 200 . In operation of decoder 200 , a sequence of blocks of the bitstream are presented from buffer 201 to deformatter 205 .

In a variation of the FIG. 3 embodiment (or the FIG. 4 embodiment discussed below), a non-decoder APU (eg, APU 500 of FIG. 6) uses the same type of data received by buffer 201 of FIG. 3 or FIG. Store (e.g., in a non-transitory manner) at least one block of an encoded audio bitstream (e.g., an MPEG-4 AAC audio bitstream) (i.e., an encoded audio bitstream containing eSBR metadata) buffer memory (eg, the same buffer memory as buffer 201).

Referring again to FIG. 3, the deformatter 205 demultiplexes each block of the bitstream and then removes SBR metadata (including quantized envelope data) and eSBR metadata (typically other metadata) and presents at least said eSBR metadata and said SBR metadata to eSBR processing stage 203, and typically further other extracted metadata to decoding subsystem 202 (optionally is also coupled to and configured to provide control bit generator 204). Deformatter 205 is also coupled and configured to extract audio data from each block of the bitstream and present the extracted audio data to decoding subsystem (decoding stage) 202 .

The system of FIG. 3 optionally also includes post-processor 300 . Post-processor 300 includes a buffer memory (buffer) 301 and other processing elements (not shown) including at least one processing element coupled to buffer 301 . Buffer 301 stores (eg, in a non-transitory manner) at least one block (or frame) of decoded audio data received by post-processor 300 from decoder 200 . The processing elements of post-processor 300 receive the sequence of blocks (or frames) of decoded audio output from buffer 301, and the metadata output from decode subsystem 202 (and/or deformatter 205). coupled and configured to adaptively process using data and/or control bits output from stage 204 of decoder 200;

Audio decoding subsystem 202 of decoder 200 decodes the audio data extracted by parser 205 (such decoding may be referred to as a "core" decoding operation) to produce decoded audio data and present the decoded audio data to the eSBR processing stage 203 . Decoding is performed in the frequency domain and typically includes inverse quantization followed by spectral processing. Typically, the final stage of processing in subsystem 202 applies a frequency-domain to time-domain transform to the decoded frequency-domain audio data, so that the output of the subsystem is time-domain decoded audio data. Data. Stage 203 applies the SBR and eSBR tools indicated by the SBR and eSBR metadata (extracted by parser 205) to the decoded audio data (i.e., using the SBR and eSBR metadata It is configured to perform SBR and eSBR processing on the output of decoding subsystem 202) to produce fully decoded audio data that is output from decoder 200 (eg, to post-processor 300). Typically, decoder 200 includes a memory (accessible by subsystem 202 and stage 203) that stores the unformatted audio data and metadata output from deformatter 205, stage 203 being SBR and It is configured to access audio data and metadata (including SBR metadata and eSBR metadata) as needed during eSBR processing. The SBR and eSBR processing in stage 203 may be considered post-processing on the output of core decode subsystem 202 . Optionally, the decoder 200 uses the final upmix subsystem (which uses the PS metadata extracted by the deformatter 205 and/or the control bits generated in the subsystem 204 to create an MPEG-4 Parametric Stereo ("PS") tool defined in the AAC standard may be applied). An upmix subsystem is coupled and configured to perform an upmix on the output of stage 203 to produce fully decoded, upmixed audio output from decoder 200 . Alternatively, post-processor 300 performs an upmix on the output of decoder 200 (eg, using PS metadata extracted by deformatter 205 and/or control bits generated in subsystem 204). Configured.

In response to the metadata extracted by deformatter 205, control bits generator 204 may generate control data. The control data may be used within decoder 200 (eg, in the final upmix subsystem) and/or presented as an output of decoder 200 (eg, to post-processor 300 for use in post-processing). may In response to metadata extracted from the input bitstream (and optionally in response to control data), stage 204 determines whether the decoded audio data output from eSBR processing stage 203 is of a particular type. A control bit may be generated (presented to post-processor 300) indicating that it should undergo post-processing. In some implementations, the decoder 200 is configured to present the metadata extracted by the deformatter 205 from the input bitstream to the post-processor 300, which applies the decoded metadata output from the decoder 200. It is configured to perform post-processing on the audio data using said metadata.

FIG. 4 is a block diagram of an audio processing unit (“APU”) (210), which is another embodiment of the audio processing unit of the present invention. APU 210 is a legacy decoder that is not configured to perform eSBR processing. Any of the components or elements of APU 210 may be implemented in hardware, software, or a combination of hardware and software, as one or more processes and/or one or more circuits (e.g., ASICs, FPGAs, or other integrated circuits). , may be implemented. APU 210 includes a buffer memory 201, a bitstream payload de-formatter (parser) 215, an audio decoding subsystem 202 (sometimes a "core" decoding stage or "core" decoding stage), connected as shown. subsystem) and SBR processing stage 213 . Typically, APU 210 also includes other processing elements (not shown).

Elements 201 and 202 of APU 210 are identical to the same numbered elements of decoder 200 (of FIG. 3) and the above description thereof will not be repeated. In operation of APU 210 , a sequence of blocks of encoded audio bitstream (MPEG-4 AAC bitstream) received by APU 210 is presented from buffer 201 to deformatter 215 .

De-formatter 215 de-multiplexes each block of the bitstream and extracts SBR metadata (including quantized envelope data) from it, and typically other metadata as well, but the optional are combined and configured to ignore any eSBR that may be included in the bitstream according to the embodiment of . The deformatter 215 is configured to present at least said SBR metadata to the SBR processing stage 213 . Deformatter 215 is also coupled and configured to extract audio data from each block of the bitstream and present the extracted audio data to decoding subsystem (decoding stage) 202 .

Audio decoding subsystem 202 of decoder 200 decodes the audio data extracted by deformatter 215 (such decoding may be referred to as a "core" decoding operation) to produce the decoded audio • configured to generate data and present the decoded audio data to the SBR processing stage 213; Decoding is performed in the frequency domain. Typically, the final stage of processing in subsystem 202 applies a frequency-domain to time-domain transform to the decoded frequency-domain audio data, so that the output of the subsystem is time-domain decoded audio data. Data. Stage 213 applies the SBR tools (but no eSBR tools) indicated by the SBR metadata (extracted by deformatter 215) to the decoded audio data (i.e., using the SBR metadata It is configured to perform SBR processing on the output of the decoding subsystem 202) to produce fully decoded audio data that is output from the APU 210 (eg, to the post-processor 300). Typically, APU 210 includes memory (accessible by subsystem 202 and stage 213) that stores the unformatted audio data and metadata output from deformatter 215, which stage 213 performs SBR processing. configured to access audio data and metadata (including SBR metadata) as needed during The SBR processing in stage 213 may be considered post-processing on the output of core decode subsystem 202 . Optionally, the APU 210 performs a final upmix subsystem (which uses the PS metadata extracted by the deformatter 215 to convert parametric stereo (" PS”) tool may be applied). An upmix subsystem is coupled and configured to perform an upmix on the output of stage 213 to produce fully decoded, upmixed audio output from APU 210 . Alternatively, the post-processor is configured to perform upmixing on the output of APU 210 (eg, using PS metadata extracted by deformatter 215 and/or control bits generated at APU 210). be.

Various implementations of encoder 100, decoder 200 and APU 210 are configured to perform different embodiments of the method of the present invention.

According to some embodiments, legacy decoders (not configured to parse eSBR metadata or use any eSBR tools that involve eSBR metadata) ignore eSBR metadata, but still If the eSBR metadata is ( For example, a few control bits that are eSBR metadata) are included in the encoded audio bitstream (eg MPEG-4 AAC bitstream). However, an eSBR decoder that is configured to parse a bitstream to identify eSBR metadata and use at least one eSBR tool in response to the eSBR metadata may be unable to use at least one such eSBR tool. enjoy the benefits. Accordingly, embodiments of the present invention provide a means of efficiently transmitting enhanced spectral band replication (eSBR) control data or metadata in a backward compatible manner.

Typically, eSBR metadata in a bitstream is generated using one of the following eSBR tools (described in the MPEG USAC standard, which may or may not have been applied by the encoder during bitstream generation): Indicate one or more (e.g., indicate at least one characteristic or parameter of one or more of the following eSBR tools):
- harmonic conversion;
- QMF patching additional pre-processing (pre-flattening); and - sub-band inter-sample Temporal Envelope Shaping or "inter-TES".
For example, the eSBR metadata included in the bitstream can be represented by parameters (described in the MPEG USAC standard and this disclosure): harmonicSBR[ch], sbrPatchingMode[ch], sbrOversamplingFlag[ch], sbrPitchInBins[ch], sbrPitchInBins[ch] , bs_interTes, bs_temp_shape[ch][env], bs_inter_temp_shape_mode[ch][env] and bs_sbr_preprocessing.

Here, the notation X[ch], where X is some parameter, denotes that the parameter relates to a certain channel ("ch") of the audio content of the encoded bitstream to be decoded. For simplicity, we sometimes omit the expression [ch] and assume that the relevant parameters relate to a certain channel of audio content.

where the notation X[ch][env] is the SBR envelope ("env ”). For simplicity, we sometimes omit the expressions [env] and [ch] and assume that the relevant parameters relate to the SBR envelope of a certain channel of audio content.

As mentioned above, MPEG USAC contemplates that the USAC bitstream contains eSBR metadata that controls the execution of eSBR processing by decoders. eSBR metadata includes the following one-bit metadata parameters: harmonicSBR; bs_interTES; and bs_pvc.

The parameter harmonicSBR indicates the use of harmonic patching (harmonic transposition) for SBR. Specifically, harmonicSBR=0 indicates non-harmonic spectral patching as described in section 4.6.18.6.3 of the MPEG-4 AAC standard; Fig. 7 shows harmonic SBR patching (of the type used in eSBR, described in Section 7.5.3 or 7.5.4). Harmonic SBR patching is not used with non-eSBR spectral band replication (ie, SBR that is not eSBR). Throughout this disclosure, the basic form of spectral band replication is referred to as spectral patching, and the enhanced form of spectral band replication is referred to as harmonic transposition.

The value of the parameter bs_interTES indicates the use of eSBR's interTES tool.

The value of parameter bs_pvc indicates the use of eSBR's PVC tool.

During decoding of an encoded bitstream, the performance of harmonic conversion between the eSBR processing stages of decoding (for each channel "ch" of the audio content indicated by the bitstream) is determined by the following eSBR metadata parameters: sbrPatchingMode[ch]; sbrOversamplingFlag[ch]; sbrPitchInBinsFlag[ch] and sbrPitchInBins[ch].

The value of sbrPatchingMode[ch] indicates the type of transposer used in eSBR. sbrPatchingMode[ch]=1 indicates non-harmonic patching as described in clause 4.6.18.6.3 of the MPEG-4 AAC standard; sbrPatchingMode[ch]=0 indicates clause 7.5.3 or 7.5.4 of the MPEG USAC standard. shows harmonic SBR patching as described in .

The value of sbrOversamplingFlag[ch] indicates the use of signal adaptive frequency domain oversampling in eSBR combined with DFT-based harmonic SBR patching as described in section 7.5.3 of the MPEG USAC standard. This flag controls the size of the DFT used in the converter. 1 indicates signal adaptive frequency domain oversampling enabled as described in Section 7.5.3.1 of the MPEG USAC Standard; 0 indicates disabled as described in Section 7.5.3.1 of the MPEG USAC Standard. signal adaptive frequency domain oversampling.

The value of sbrPitchInBinsFlag[ch] controls the interpretation of the sbrPitchInBins[ch] parameter. 1 indicates that the value in sbrPitchInBins[ch] is valid and greater than 0; 0 indicates that the value of sbrPitchInBins[ch] is set to zero.

The value of sbrPitchInBins[ch] controls the addition of cross product terms in the SBR harmonic converter. The value sbrPitchInBins[ch] is an integer value in the range [0,127] and represents the distance measured in frequency bins for the 1536-line DFT operating on the sampling frequency of the core encoder.

If the MPEG-4 AAC bitstream exhibits a pair of SBR channels whose channels are not combined (rather than a single SBR channel), then the bitstream is represented in the above syntax (for harmonic or non-harmonic conversion). Show two instances. One instance for each channel of sbr_channel_pair_element().

Harmonic conversion in eSBR tools typically improves the quality of decoded music signals at relatively low crossover frequencies. Harmonic conversion should be implemented by DFT-based or QMF-based harmonic conversion in the decoder. Non-harmonic conversion (ie, legacy spectral patching or copying) typically improves speech signals. Thus, the starting point in determining which type of transformation is preferable for encoding a particular audio content is to choose the transformation method depending on the speech/music detection. Here, harmonic conversion is used for musical content and spectral patching is used for speech content.

The performance of pre-flattening during eSBR processing is controlled by the value of a one-bit eSBR metadata parameter known as bs_sbr_preprocessing. That is in the sense that pre-flattening is performed or not depending on the value of this single bit. When the SBR QMF patching algorithm described in section 4.6.18.6.3 of the MPEG-4 AAC standard is used, a discontinuity in the shape of the spectral envelope of the high-frequency signal is detected by the subsequent envelope adjuster. A stage of pre-flattening may be performed (when indicated by the bs_sbr_preprocessing parameter) in an attempt to avoid being input to (performing another stage of eSBR processing). Pre-flattening typically improves the operation of subsequent envelope adjustment stages, resulting in a more stable perceived high-pass signal.

Performing inter-subband sample Temporal Envelope Shaping (“Inter-TES” tool) during eSBR processing in the decoder is performed on each channel of the audio content of the decoded USAC bitstream ( 'ch')) controlled by the following eSBR metadata parameters for each SBR envelope ('env'): bs_temp_shape[ch][env] and bs_inter_temp_shape_mode[ch][env].

The InterTES tool processes the QMF subband samples after the envelope adjuster. This processing stage shapes the temporal envelope of the higher frequency band with a finer temporal granularity than that of the envelope adjuster. Inter-TES shapes the temporal envelope between QMF subband samples by applying a gain factor to each QMF subband sample in the SBR envelope.

Parameter bs_temp_shape[ch][env] is a flag that signals the use of inter-TES. Parameter bs_inter_temp_shape_mode[ch][env] indicates the value of parameter γ in inter TES (as defined in the MPEG USAC standard).

The overall bitrate requirement for including eSBR metadata indicating the eSBR tools mentioned above (harmonic conversion, preflattening and inter-TES) in an MPEG-4 AAC bitstream is on the order of hundreds of bits per second. Be expected. This is because, according to some embodiments of the present invention, only the differential control data required to perform eSBR processing is transmitted. This information is included in a backwards compatible manner (as explained below) so that legacy decoders can ignore this information. Therefore, the negative impact on bitrate associated with including eSBR metadata is negligible for several reasons, including:
The bitrate penalty (due to the inclusion of eSBR metadata) is that only differential control data needed to perform eSBR processing is transmitted (no simulcast of SBR control data) be a very small percentage of the total bitrate;
- The tuning of SBR-related control information is typically independent of the details of the conversion; to run.

Thus, embodiments of the present invention provide a means of efficiently transmitting enhanced spectral band replication (eSBR) control data or metadata in a backward compatible manner. This efficient transmission of eSBR control data reduces memory requirements in decoders, encoders and transcoders employing aspects of the present invention, without any appreciable adverse impact on bitrate. Furthermore, the complexity and processing demands associated with performing eSBR according to embodiments of the present invention are also reduced. SBR data only needs to be processed once, and eSBR is treated as a completely separate object type in MPEG-4 AAC rather than being integrated into the MPEG-4 AAC codec in a backwards compatible manner. This is because it does not need to be simulcast as it would be if

Referring now to FIG. 7, the elements of an MPEG-4 AAC bitstream block (raw_data_block) in which eSBR metadata is included according to some embodiments of the present invention are described. FIG. 7 is a block diagram (raw_data_block) of an MPEG-4 AAC bitstream showing some of its segments.

A block of an MPEG-4 AAC bitstream contains at least one single_channel_element() (eg, the single channel element shown in FIG. 7) and/or at least one channel_pair_element() (see FIG. 7) containing audio data for an audio program. 7 may include (although not specifically shown, may be present). A block may also contain a number of fill_elements (eg, fill element 1 and/or fill element 2 in FIG. 7) that contain program-related data (eg, metadata). Each single_channel_element( ) contains an identifier (eg, “ID1” in FIG. 7) that indicates the beginning of a single channel element and can contain audio data that indicates different channels of a multi-channel audio program. Each channel_pair_element contains an identifier (not shown in FIG. 7) that indicates the beginning of the channel pair element and can contain audio data that indicates two channels of the program.

A fill_element (referred to herein as a fill element) of an MPEG-4 AAC bitstream includes an identifier (eg, "ID2" in FIG. 7) that indicates the beginning of the fill element, followed by fill data. The identifier ID2 may consist of a 3-bit unsigned integer ("uimsbf") with a value of 0x6, with the most significant bit transmitted first. Fill data can include an extension_payload() element (sometimes referred to herein as an extension payload). Its syntax is shown in Table 4.57 of the MPEG-4 AAC Standard. Several types of extension payloads exist, identified through the extension_type parameter. This parameter is a 4-bit unsigned integer ("uimsbf") with the most significant bit transmitted first.

The filler data (eg, its extension payload) may include a header or identifier (eg, "header 1" in FIG. 7) that indicates a segment of the filler data that indicates an SBR object (i.e., if the header is specified in the MPEG-4 AAC standard as Initialize an "SBR Object" type called sbr_extension_data()). For example, a Spectrum Band Replication (SBR) extension payload is identified with a value of '1101' or '1110' for the extension_type field in the header, where the identifier '1101' identifies an extension payload using SBR data, and '1110' Identify an extension payload using SBR data with a cyclic redundancy check (CRC) to verify the correctness of the SBR data.

When the header initializes the SBR object type (e.g. the extension_type field), the header contains SBR metadata (sometimes referred to in this document as "spectrum band replication data" and in the MPEG-4 AAC standard as sbr_data() ), and the SBR metadata may be followed by at least one spectral band duplication extension element (eg, “SBR extension element” in fill element 1 of FIG. 7). Such spectrum band replication extension elements (bitstream segments) are called sbr_extension( ) containers in the MPEG-4 AAC standard. The spectral band duplication extension element optionally includes a header (eg, "SBR Extension Header" in filler element 1 of FIG. 7).

The MPEG-4 AAC standard allows for spectral band replication extension elements to contain PS (parametric stereo) data for program audio data. The MPEG-4 AAC standard specifies that the header of the filler element (e.g. its extension payload) initializes the SBR object type (as in "Header 1" in Figure 7) and the Spectral Band Duplication extension element of the filler element carries the PS data. When included, it is contemplated that the filler element (eg its extension payload) includes the spectrum band duplication data bs_extension_id parameter. A value of this parameter (ie bs_extension_id=2) indicates that the PS data is included in the spectral band replication extension element of the filler element.

According to some embodiments of the present invention, eSBR metadata (e.g., a flag indicating whether enhanced spectral band replication (eSBR) processing is to be performed on the audio content of that block) is specified in the spectral band of the filler element. Included in the replication extension element. For example, such a flag is included in filler element 1 of FIG. 7, where the flag appears after the "SBR Extension Header" of filler element 1 ("SBR Extension Header" of filler element 1). Optionally, such flags and additional eSBR metadata are provided in the spectral band duplication extension element after the header of the spectral band duplication extension element (e.g., in the SBR extension element of fill element 1 in FIG. 7, after the SBR extension header ) are included. According to some embodiments of the invention, a filler element containing eSBR metadata also contains a bs_extension_id parameter. The value of that parameter (eg bs_extension_id=3) indicates that the filler element contains eSBR metadata and eSBR processing should be performed on the audio content of that block.

According to some embodiments of the present invention, the eSBR metadata is a filler element of an MPEG-4 AAC bitstream other than the spectral band replication extension element (SBR extension element) of the filler element (eg, filler 2 in FIG. 7). be included in This is because a filler element containing extension_payload() with SBR data or SBR data with CRC does not contain any other extension payload of any other extension type. Therefore, in embodiments where the eSBR metadata is stored in its own extension payload, a separate filler element is used to store the eSBR metadata. Such filler elements include an identifier (eg, "ID2" in FIG. 7) that indicates the beginning of the filler element, followed by the filler data. Fill data can include an extension_payload() element (sometimes referred to herein as an extension payload). Its syntax is shown in Table 4.57 of the MPEG-4 AAC Standard. The filler data (eg, its extension payload) may include a header (eg, "header 2" of filler element 2 in FIG. 7) that indicates an eSBR object (i.e., the header indicates an enhanced spectral band replication (eSBR) object type). initialization), the filler data (eg its extension payload) contains the eSBR metadata after the header. For example, filler element 2 in FIG. 7 contains such a header (“header 2”), after which eSBR metadata (i.e., the enhanced spectral band replication (eSBR) processing is applied to the audio content of that block). It also contains a "flag" in filler element 2) that indicates whether or not it is executed. Optionally, additional eSBR metadata is also included in the filler data for filler element 2 in FIG. 7 after header 2 . In the embodiment described in this paragraph, the header (e.g. Header 2 in Figure 7) indicates an eSBR extension payload rather than one of the normal values specified in Table 4.57 of the MPEG-4 AAC standard. It has an identity value (thus the extension_type field in the header indicates that the filler data contains eSBR metadata).

In a first class of embodiments, the invention is an audio processing unit (e.g. decoder) which:
a memory (eg, buffer 201 of FIG. 3 or 4) configured to store at least one block of an encoded audio bitstream (eg, at least one block of an MPEG-4 AAC bitstream);
a bitstream payload de-formatter (e.g., element 205 of FIG. 3 or element 215 of FIG. 4) coupled to the memory and configured to demultiplex at least a portion of the blocks of the bitstream;
a decoding subsystem (e.g., elements 202 and 203 of FIG. 3 or elements 202 and 213 of FIG. 4) coupled and configured to decode at least one portion of audio content of said block of said bitstream. and said block is
including a filler element, an identifier indicating the beginning of the filler element (e.g., an id_syn_ele identifier with value 0x6 in Table 4.85 of the MPEG-4 AAC Standard) and filler data after the identifier, said filler data being:
At least one flag identifying whether enhanced spectral band replication (eSBR) processing should be performed on the audio content of the block (eg, using spectral band replication data and eSBR metadata included in the block). including,
Audio processing unit.

Said flag is eSBR metadata and an example of said flag is the sbrPatchingMode flag. Another example of said flag is the harmonicSBR flag. Both of these flags indicate whether a basic form of spectral band duplication or an enhanced form of spectral band duplication should be performed on the block of audio data. The basic form of spectral replication is spectral patching, and the enhanced form of spectral band replication is harmonic conversion.

In some embodiments, the fill data also includes additional eSBR metadata (ie, eSBR metadata other than the flag).

The memory may be a buffer memory (eg, an implementation of buffer 201 of FIG. 4) that stores (eg, in a non-transient manner) the at least one block of an encoded audio bitstream.

eSBR processing (using eSBR harmonic conversion, preflattening and inter-TES tools) by an eSBR decoder during decoding of an MPEG-4 AAC bitstream containing eSBR metadata (the eSBR metadata indicates these eSBR tools) ) is estimated to be (for a typical decoding with the parameters shown):
●Harmonic conversion (16kbps, 14400/28800Hz)
○ DFT-based: 3.68 WMOPS (weighted million operations per second);
○ WMF base: 0.98 WMOPS;
QMF patching pretreatment (pre-flattening): 0.1 WMOPS;
Sub-band inter-sample temporal envelope shaping (inter-TES): 0.16 WMOPS at most
For transient components, DFT-based transformations are found to typically perform better than QMF-based transformations.

According to some embodiments of the present invention, a filler element (of an encoded audio bitstream) containing eSBR metadata indicates that the eSBR metadata is included in the filler element and for the audio content of the block. A parameter (e.g. bs_extension_id parameter) with a value (e.g. bs_extension_id = 3) signaling that eSBR processing should be performed on the Also include parameters with bs_extension_id=2) (eg same bs_extension_id parameter). For example, as shown in Table 1 below, such a parameter with value bs_extension_id=2 may signal that the filler element's sbr_extension() container contains PS data, and has value bs_extension_id=3. Such parameters may signal that the filler element's sbr_extension() container contains eSBR metadata.

本発明のいくつかの実施形態によれば、eSBRメタデータおよび／またはPSデータを含む各スペクトル帯域複製拡張要素のシンタックスは下記の表２に示されるとおりである（ここで、sbr_extension()はスペクトル帯域複製拡張要素であるコンテナを表わし、bs_extension_idは上記の表１で述べたとおりであり、ps_dataはPSデータを表わし、esbr_dataはeSBRメタデータを表わす）。

According to some embodiments of the present invention, the syntax of each spectral band replication extension element containing eSBR metadata and/or PS data is as shown in Table 2 below (where sbr_extension() is bs_extension_id is as described in Table 1 above, ps_data represents PS data, and esbr_data represents eSBR metadata).

ある例示的実施形態では、上記の表２で言及されているesbr_data()は以下のメタデータ・パラメータの値を示す。
１．上記の一ビットのメタデータ・パラメータharmonicSBR；bs_interTES；およびbs_sbr_preprocessing；
２．デコードされるべきエンコードされたビットストリームのオーディオ・コンテンツの各チャネル（「ch」）について、上記のパラメータ：sbrPatchingMode[ch]；sbrOversamplingFlag[ch]；sbrPitchInBinsFlag[ch]；およびsbrPitchInBins[ch]のそれぞれ；および
３．デコードされるべきエンコードされたビットストリームのオーディオ・コンテンツの各チャネル（「ch」）の各SBR包絡（「env」）について、上記のパラメータ：bs_temp_shape[ch][env]；およびbs_inter_temp_shape_mode[ch][env]のそれぞれ。

In one exemplary embodiment, the esbr_data() referred to in Table 2 above indicates the values of the following metadata parameters.
1. the above one-bit metadata parameters harmonicSBR; bs_interTES; and bs_sbr_preprocessing;
2. For each channel ("ch") of the audio content of the encoded bitstream to be decoded, each of the above parameters: sbrPatchingMode[ch]; sbrOversamplingFlag[ch]; sbrPitchInBinsFlag[ch]; and sbrPitchInBins[ch]; and 3. For each SBR envelope ("env") for each channel ("ch") of the audio content of the encoded bitstream to be decoded, the above parameters: bs_temp_shape[ch][env]; and bs_inter_temp_shape_mode[ch][ env] respectively.

For example, in some embodiments, esbr_data() may have the syntax shown in Table 3 to indicate these metadata parameters.

表３では、中央の列における数字は左の列における対応するパラメータのビット数を示す。

In Table 3, the numbers in the middle column indicate the number of bits of the corresponding parameter in the left column.

The above syntax allows efficient implementation of enhanced forms of spectral band duplication, such as harmonic conversion, as an extension to legacy decoders. Specifically, the eSBR data in Table 3 are the parameters required to perform an enhanced form of spectral band duplication that are already supported in the bitstream or already supported in the bitstream. includes only material that is not or is not directly retrievable from All other parameters and processing data required to perform the enhanced form of spectral band replication are extracted from existing parameters at locations already defined in the bitstream. This is in contrast to alternative (more inefficient) implementations that simply transmit all of the processing metadata used for enhanced spectral band duplication.

For example, MPEG-4 HE-AAC or HE-AAC-v2 compliant decoders may be extended to include enhanced forms of spectral band duplication such as harmonic conversion. This enhanced form of spectral band replication is in addition to the basic form of spectral band replication already supported by the decoder. In the context of MPEG-4 HE-AAC or HE-AAC-v2 compliant decoders, this basic form of spectral band replication is the QMF spectral patching SBR tool defined in section 4.6.18 of the MPEG-4 AAC standard.

When performing an enhanced form of spectral band duplication, the enhanced HE-AAC decoder may reuse many of the bitstream parameters already included in the bitstream's SBR extension payload. Specific parameters that can be reused include, for example, various parameters that determine the master frequency band table. These parameters are bs_start_freq (the parameter that determines the start of the master frequency table parameter), bs_stop_freq (the parameter that determines the end of the master frequency table), bs_freq_scale (the parameter that determines the number of frequency bands per octave) and bs_alter_scale (the parameters that change the scale of the frequency band). Parameters that can be reused also include parameters that determine the noise band table (bs_noise_bands) and limiter band table parameters (bs_limiter_bands).

In addition to many of the parameters described above, other data elements may also be reused by the enhanced HE-AAC decoder when performing an enhanced form of spectral band duplication according to embodiments of the present invention. For example, envelope data and noise floor data may be extracted from bs_data_env and bs_noise_env data and used during an enhanced form of spectral band replication.

In essence, these embodiments use the configuration parameters and envelope data already supported by legacy HE-AAC or HE-AAC v2 decoders in the SBR extension payload with as little additional transmission data as possible. to enable an improved form of spectral band duplication. Thus, an enhanced decoder that supports an improved form of spectral band duplication relies on the already defined bitstream elements (e.g., those in the SBR extension payload) to support an improved form of spectral band duplication. can be generated in a very efficient manner by adding (into the filler element extension payload) only the parameters that This data reduction feature, combined with placing the newly added parameters into reserved data fields such as the extension container, allows the bitstream to be used with legacy decoders that do not support an enhanced form of spectral band duplication. By ensuring backward compatibility, the barrier to creating decoders that support an improved form of spectral band duplication is substantially reduced.

In some embodiments, the invention is a method that includes encoding audio data to produce an encoded bitstream (eg, MPEG-4 AAC bitstream). The generating includes by including eSBR metadata in at least one segment of at least one block of the encoded bitstream and audio data in at least one other segment of said block. In an exemplary embodiment, the method includes multiplexing audio data with eSBR metadata in each block of the encoded bitstream. In typical decoding of said encoded bitstream in an eSBR decoder, the decoder extracts the eSBR metadata from the bitstream (this includes by parsing and demultiplexing the eSBR metadata and audio data). , uses the eSBR metadata to process the audio data to produce a stream of decoded audio data.

Another aspect of the invention is that during decoding of encoded audio bitstreams (e.g. MPEG-4 AAC bitstreams) that do not contain eSBR metadata (e.g. harmonic conversion, preflattening or inter-TES An eSBR decoder configured to perform eSBR processing using at least one of the eSBR tools known as eSBR tools. An example of such a decoder is described with reference to FIG.

The eSBR decoder (400) of FIG. 5 comprises a buffer memory 201 (which is identical to the memory 201 of FIGS. 3 and 4) and a bitstream payload deformatter 215 (which is a 4) and an audio decoding subsystem 202 (sometimes referred to as the "core" decoding stage or "core" decoding subsystem, identical to the core decoding subsystem 202 of FIG. 3). ), an eSBR control data generation subsystem 401, and an eSBR processing stage 203 (which is identical to stage 203 in FIG. 3). Decoder 400 typically also includes other processing elements (not shown).

In operation of decoder 400 , a sequence of blocks of encoded audio bitstream (MPEG-4 AAC bitstream) received by decoder 400 is presented from buffer 201 to deformatter 215 .

De-formatter 215 is coupled and configured to de-multiplex each block of the bitstream and extract therefrom the SBR metadata (including the quantized envelope data), and typically other metadata as well. be. The deformatter 215 is configured to present at least said SBR metadata to the eSBR processing stage 203 . Deformatter 215 is also coupled and configured to extract audio data from each block of the bitstream and present the extracted audio data to decoding subsystem (decoding stage) 202 .

Audio decoding subsystem 202 of decoder 400 decodes the audio data extracted by deformatter 215 (such decoding may be referred to as a "core" decoding operation) to produce the decoded audio • configured to generate data and present the decoded audio data to the eSBR processing stage 203; Decoding is performed in the frequency domain. Typically, the final stage of processing in subsystem 202 applies a frequency-domain to time-domain transform to the decoded frequency-domain audio data, so that the output of the subsystem is time-domain decoded audio data. Data. Stage 203 applies the SBR tools (and eSBR tools) indicated by the SBR metadata (extracted by deformatter 215) and the eSBR metadata generated in subsystem 401 to the decoded audio data. configured to produce fully decoded audio data output from decoder 400 (i.e., perform SBR and eSBR processing on the output of decoding subsystem 202 using SBR and eSBR metadata). be done. Typically, decoder 400 has a memory (accessed by subsystem 202 and stage 203) that stores unformatted audio data and metadata output from deformatter 215 (and optionally subsystem 401). possible), and stage 203 is configured to access audio data and metadata as needed during SBR and eSBR processing. The SBR processing in stage 203 may be considered post-processing on the output of core decode subsystem 202 . Optionally, the decoder 400 uses the final upmix subsystem (which uses the PS metadata extracted by the deformatter 215 to convert parametric stereo (" PS”) tool may be applied). An upmix subsystem is coupled and configured to perform an upmix on the output of stage 203 to produce fully decoded, upmixed audio output from APU 210 .

The control data generation subsystem 401 of FIG. 5 detects at least one attribute of the encoded audio bitstream to be decoded and, in response to at least one result of the detection step, eSBR control data (which is according to another embodiment of the invention, to produce eSBR metadata of any type contained in the encoded audio bitstream). configured. eSBR control data is presented to stage 203 to trigger the application of individual eSBR tools or combinations of eSBR tools and/or such when certain attributes (or combinations of attributes) of the bitstream are detected. control the application of various eSBR tools. For example, to control the execution of eSBR processing using harmonic conversion, some embodiments of control data generation subsystem 401: In response to detecting that the bitstream indicates or does not indicate music: A music detector (e.g., a simplified version of a regular music detector) for setting the sbrPatchingMode[ch] parameter (and presenting the set parameter to stage 203); a transient detector for setting the sbrOversamplingFlag[ch] parameter (and presenting the set parameter to stage 203) in response to detecting the presence or absence of a transient; A pitch detector will be included for setting the sbrPitchInBinsFlag[ch] and sbrPitchInBins[ch] parameters (and presenting the set parameters to stage 203) in response to detecting the pitch of the content. Another aspect of the invention is an audio bitstream decoding method performed by any of the embodiments of the decoder of the invention described in this paragraph and the previous paragraph.

Aspects of the present invention include encoding or decoding methods of the type that any embodiment of the APU, system or device of the present invention is configured (eg, programmed) to perform. Other aspects of the invention include systems or devices configured (eg programmed) to perform any embodiment of the method of the invention and implementing any embodiment of the method of the invention or steps thereof. computer readable medium (eg, disk) that stores (eg, in a non-transitory manner) code for For example, the system of the present invention may comprise software or software such that a programmable general purpose processor, digital signal processor or microprocessor performs any of a variety of operations on data, including embodiments of the method of the present invention or steps thereof. It may be or include programmed with firmware and/or otherwise configured. Such a general-purpose processor is a computer system comprising input devices, memory and processing circuitry programmed to perform an embodiment (or steps thereof) of the method of the present invention in response to data presented thereto ( and/or otherwise configured).

Embodiments of the invention may be implemented in hardware, firmware or software, or a combination of both (eg, as a programmable logic array). Unless specified otherwise, the algorithms or processes included as part of the invention are not inherently related to any particular computer or other apparatus. In particular, various general-purpose machines may be used with programs written in accordance with the teachings herein, or construct more specialized apparatus (eg, integrated circuits) to perform the required method steps. It may be more convenient. Thus, the present invention may be implemented in one or more programmable computer systems (e.g., elements of FIG. 1 or encoder 100 (or some element thereof) of FIG. 2 or decoder 200 (or some element thereof) of FIG. 3 or 4 (or some element thereof) or any implementation of decoder 400 (or some element thereof) of FIG. 5). Each computer system has at least one processor, at least one data storage system (including volatile and nonvolatile memory and/or storage elements), at least one input device or port, and at least one output device or port. and Program code is applied to input data to perform the functions described herein and generate output information. The output information is applied to one or more output devices in known fashion.

Each such program may be implemented in any desired computer language (including machine language, assembly or a high level procedural, logical or object oriented programming language) to communicate with a computer system. . In any case, the language can be a compiled or interpreted language.

For example, when implemented by computer software instruction sequences, the various functions and steps of embodiments of the invention may be implemented by multi-threaded software instruction sequences running on suitable digital signal processing hardware, where , the various devices, steps and functions of the embodiments may correspond to portions of software instructions.

Each such computer system is preferably stored on or downloaded from a general purpose or special purpose programmable computer readable storage medium or device (e.g., semiconductor memory or medium or magnetic or optical medium). . To configure and operate a computer to perform the procedures described herein when the storage medium or device is read by a computer system. The system of the present invention may be implemented as a computer-readable storage medium configured with (ie, having stored thereon) a computer program. Here, the storage medium so configured causes the computer system to operate in a specific predefined manner to perform the functions described herein.

A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications can be made without departing from the spirit and scope of the invention. Many modifications and variations of the present invention are possible in light of the above teachings. It is understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein. Any reference signs contained in the claims are for illustrative purposes only and shall not be used to interpret or limit the claims in any way.

Some aspects are described.
[Aspect 1]
a buffer configured to store at least one block of an encoded audio bitstream;
a bitstream payload de-formatter coupled to said buffer and configured to demultiplex at least a portion of said at least one block of said encoded audio bitstream;
a decoding subsystem coupled to the bitstream payload de-formatter and configured to decode at least a portion of the at least one block of the encoded audio bitstream. and said at least one block of said encoded audio bitstream is:
A filler element having an identifier indicating the beginning of the filler element and filler data following the identifier, the filler data comprising:
At least one flag identifying whether a basic form of spectral band duplication or an enhanced form of spectral band duplication is to be performed on the audio content of the at least one block of the encoded audio bitstream. including,
audio processing unit.
[Aspect 2]
said base form of spectral band replication comprising spectral patching, said enhanced form of spectral band replication comprising harmonic conversion, said filling data further comprising enhanced spectral band replication metadata, said enhanced spectral band replication metadata does not include one or more parameters used for both spectral patching and harmonic conversion.
[Aspect 3]
3. The audio processing unit of aspect 2, wherein the one or more parameters used for both spectral patching and harmonic conversion are included in an expansion payload of a filler element.
[Aspect 4]
4. The audio processing unit of aspects 2 or 3, wherein the one or more parameters used for both spectral patching and harmonic conversion include one or more parameters defining a master frequency band table.
[Aspect 5]
4. The audio processing unit of aspects 2 or 3, wherein the one or more parameters used for both spectral patching and harmonic conversion include an envelope scale factor or a noise floor scale factor.
[Aspect 6]
6. Any one of aspects 1-5, wherein the audio processing unit is an audio decoder and the identifier is a 3-bit unsigned integer with a value of 0x6, the most significant bit being transmitted first. Audio processing unit as described.
[Aspect 7]
The filling data includes an extension payload, the extension payload includes spectral band duplication extension data, the extension payload has a value of '1101' or '1110' and is of four bits, the most significant bit being transmitted first. is identified using an unsigned integer that is
Said spectral band replication extension data is:
an optional spectral band duplication header,
spectrum band replication data after the header; and a spectrum band replication extension element after the spectrum band replication data, wherein the first flag is included in the spectrum band replication extension element.
7. An audio processing unit according to any one of aspects 1-6.
[Aspect 8]
The at least one block of the encoded audio bitstream includes a first filler element and a second filler element, the first filler element including spectral band replication data, and the second filler element. 8. The audio processing unit of any one of aspects 1-7, wherein a filler element includes the first flag but does not include spectral band replication data.
[Aspect 9]
The enhanced form of spectral band duplication includes harmonic conversion, the base form of spectral band duplication includes spectral patching, and a value of the first flag is equal to the encoded audio bitstream. , another value of the first flag indicating that the enhanced form of spectral band replication processing should be performed on the audio content of the at least one block of the encoded audio any of aspects 1-8, indicating that spectral patching should be performed on the audio content of said at least one block of a bitstream, but said harmonic conversion should not be performed; An audio processing unit according to any preceding claim.
[Aspect 10]
8. Aspect 7. The aspect 7, wherein the spectral band replication extension element includes enhanced spectral band replication metadata other than the first flag, and includes a parameter indicating whether the enhanced spectral band replication metadata performs pre-flattening. audio processing unit.
[Aspect 11]
wherein the spectral band replication extension element includes enhanced spectral band replication metadata other than the first flag, and a parameter indicating whether the enhanced spectral band replication metadata performs subband-to-sample temporal envelope shaping. 8. The audio processing unit of aspect 7, comprising:
[Aspect 12]
12. The audio processing unit of any one of aspects 1-11, further comprising an enhanced spectral band replication processing subsystem configured to perform an enhanced spectral band replication processing using the first flag.
[Aspect 13]
A second flag identifies whether signal adaptive frequency domain oversampling is enabled or disabled when said at least one flag indicates said enhanced form of spectral band replication processing. 13. An audio processing unit according to any one of claims 1-12.
[Aspect 14]
A method for decoding an encoded audio bitstream comprising:
receiving at least one block of an encoded audio bitstream;
demultiplexing at least a portion of the at least one block of the encoded audio bitstream;
decoding at least a portion of the at least one block of the encoded audio bitstream;
The at least one block of the encoded audio bitstream is:
A filler element having an identifier indicating the beginning of the filler element and filler data following the identifier, the filler data comprising:
At least one flag identifying whether a basic form of spectral band duplication or an enhanced form of spectral band duplication is to be performed on the audio content of the at least one block of the encoded audio bitstream. including,
Method.
[Aspect 15]
15. The method of aspect 14, wherein the identifier is a 3-bit, most significant bit transmitted first unsigned integer with a value of 0x6.
[Aspect 16]
said base form of spectral band replication comprising spectral patching, said enhanced form of spectral band replication comprising harmonic conversion, said filling data further comprising enhanced spectral band replication metadata, said enhanced spectral band replication metadata 16. The method of aspect 14 or 15, wherein does not include one or more parameters used for both spectral patching and harmonic conversion.
[Aspect 17]
The filling data includes an extension payload, the extension payload includes spectral band duplication extension data, the extension payload has a value of '1101' or '1110' and is of four bits, the most significant bit being transmitted first. is identified using an unsigned integer that is
Said spectral band replication extension data is:
an optional spectral band duplication header,
spectrum band replication data after the header; and a spectrum band replication extension element after the spectrum band replication data, wherein the first flag is included in the spectrum band replication extension element.
17. The method of any one of aspects 14-16.
[Aspect 18]
The enhanced form of spectral band duplication is harmonic conversion, the base form of spectral band duplication is spectral patching, and a value of the first flag is at least Another value of the first flag indicates that the enhanced form of spectral band replication processing should be performed on a block of audio content, and another value of the first flag indicates that the encoded audio bitstream is 18. The method of any one of aspects 14-17, indicating that spectral patching should be performed on the at least one block of audio content, but that the harmonic conversion should not be performed. Method.
[Aspect 19]
the spectral band replication extension element includes enhanced spectral band replication metadata other than the first flag, and includes a parameter indicating whether the enhanced spectral band replication metadata performs pre-flattening; or
wherein the spectral band replication extension element includes enhanced spectral band replication metadata other than the first flag, and a parameter indicating whether the enhanced spectral band replication metadata performs subband-to-sample temporal envelope shaping. include,
19. A method according to aspect 17 or 18.
[Aspect 20]
20. The method of any one of aspects 14-19, further comprising performing an enhanced spectral band replication process using the first flag and the second flag, wherein the enhanced spectral band replication includes harmonic conversion. the method of.
[Aspect 21]
21. The method of any one of aspects 14-20 or the audio processing unit of any one of aspects 1-8, wherein the encoded audio bitstream is an MPEG-4 AAC bitstream.

Claims (10)

An audio processing unit for decoding an encoded audio bitstream, the audio processing unit:
a bitstream payload de-formatter configured to demultiplex the encoded audio bitstream;
a decoding subsystem coupled to the bitstream payload deformatter and configured to decode the encoded audio bitstream, the encoded audio bitstream comprising:
A filler element having an identifier indicating the beginning of the filler element and filler data following the identifier, the filler data comprising:
at least one flag identifying whether a basic form of spectral band duplication or an enhanced form of spectral band duplication is to be performed on the audio content of the encoded audio bitstream;
The base form of spectral band replication comprises spectral patching, the enhanced form of spectral band replication comprises harmonic conversion, and one value of the flag is the enhanced form of spectral band replication for the audio content. indicating that spectral band replication should be performed, another value of said flag indicating that said base form spectral band replication should be performed on said audio content but said harmonic conversion should not be performed; indicate that it should not
said spectral patching copies several adjacent quadrature mirror filter (QMF) subbands from a low pass portion of an audio signal to a high pass portion of said audio signal;
audio processing unit. 2. The audio processing unit of claim 1, wherein the fill data further includes enhancement spectral band replication metadata. 3. The audio processing unit of claim 2, wherein the enhanced spectral band replication metadata is included in an extension payload of a filler element. 4. Audio processing unit according to claim 2 or 3, wherein the enhanced spectral band replication metadata comprises one or more parameters defining a master frequency band table. 4. Audio processing unit according to claim 2 or 3, wherein the encoded audio bitstream further comprises spectral band replication metadata, said spectral band replication metadata comprising envelope data or noise floor data . A method for decoding an encoded audio bitstream comprising:
demultiplexing the encoded audio bitstream;
decoding the encoded audio bitstream;
The encoded audio bitstream is:
A filler element having an identifier indicating the beginning of the filler element and filler data following the identifier, the filler data comprising:
at least one flag identifying whether a basic form of spectral band duplication or an enhanced form of spectral band duplication is to be performed on the audio content of the encoded audio bitstream;
The base form of spectral band replication comprises spectral patching, the enhanced form of spectral band replication comprises harmonic conversion, and one value of the flag is the enhanced form of spectral band replication for the audio content. indicating that spectral band replication should be performed, another value of said flag indicating that said base form spectral band replication should be performed on said audio content but said harmonic conversion should not be performed; indicate that it should not
said spectral patching copies several adjacent quadrature mirror filter (QMF) subbands from a low pass portion of an audio signal to a high pass portion of said audio signal;
Method. 7. The method of claim 6, wherein the identifier is a 3-bit unsigned integer with a value of 0x6, with the most significant bit transmitted first. 8. A method according to claim 6 or 7, wherein said filling data further comprises enhanced spectral band replication metadata. A computer readable storage medium storing program instructions which, when executed by a processor, cause the processor to perform the method of any one of claims 6 to 8. An apparatus for decoding an encoded audio bitstream, the apparatus comprising:
a memory configured to store program instructions;
a processor coupled to the memory and configured to execute the program instructions;
The program instructions, when executed by the processor, cause the processor to perform the method of any one of claims 6-8,
Device.

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