WO2013007395A1

WO2013007395A1 - Methods and devices for switching on or switching to a digital video signal with little delay

Info

Publication number: WO2013007395A1
Application number: PCT/EP2012/002967
Authority: WO
Inventors: Pierre-Alain Cotte
Original assignee: Pierre-Alain Cotte
Priority date: 2011-07-13
Filing date: 2012-07-13
Publication date: 2013-01-17
Also published as: DE102011107161A1

Abstract

The invention relates to a transmitting method for transmitting a digital video signal (11), which is originally intercoded, to a receiving device (20), having the following steps that are carried out in a server (10): receiving (200) an access request (300) with respect to the video signal (11); and transmitting (210) at least one intracoded frame (52) of a stream (51) of intracoded frames (52) of the video signal (11). The invention further relates to a receiving method for receiving a digital video signal (11), which is originally intercoded, from a server (10) with little delay, having the following steps that are carried out in a receiving device (20): receiving (100) an access request (300) with respect to the video signal (11); transmitting (110) the access request (300) to the server (10); receiving (120) at least one intracoded frame (52) of a stream (51) of intracoded frames of the video signal (11) from the server (10); decoding (130) the at least one intracoded frame (52) into at least one image frame (21); and displaying (140) the at least one decoded image frame (21) of the stream (51) of intracoded frames. The invention further relates to a server and a receiving device.

Description

Methods and devices for low-delay switching on or switching to a digital video signal

The invention relates to methods and devices by means of which switching on or switching to a digital video signal, in particular an MPEG television signal MPEG or H.264-encoded, with a respect to the prior art greatly reduced and barely for the viewer noticeable delay.

In the prior art, transmission of video signals over multicast channels results in a time delay between the moment when the particular viewer dials the video signal and the moment when the video signal is then presented to the viewer. In order to enable a transmission of a digital video signal with a low data rate, in the prior art for video signal transmissions such as DVB (terrestrial, satellite) or IP television, a coding is used that takes into account differences in temporally successive image frames and thus leads to high compression , Such encodings are eg MPEG coding (MPEG-4, MPEG-1, MPEG-2) or H.264. At certain intervals, however, a so-called keyframe is sent, which can be decoded without the knowledge of temporally adjacent frames. The delay mentioned above, which is noticeable when switching on or switching between two such coded video signals, is partly due to the fact that the receiver has to wait until the multicast data stream delivers such a keyframe, thus decoding can be started. In addition, for decoding such inter-coded video signals, a minimum number of frames must be present to the decoder so that it can produce the correct order and then decode those properly ordered frames. This also creates a delay component. Such a delay also occurs in computer programs (eg, computer games, collaborative or non-collaborative computer programs, cloud applications such as office, shared ord processing on a document, cloud gaming) in which a server generates the video output A video output for all participating users (e.g., players, shared word processing) or various video outputs for various participating users (e.g., players, videoconferencing) - and to the one or more participating user sent. The event which causes a change in the video signal is (analogous to the switching in television) an action of a user, due to which there is a change in the program and thus also in the video signal of the program.

In the article "Analysis of zapping times and IP-TV" by Peter Siebert at al. For a reduction in the switch delay, it is proposed to send a unicast video stream as a replica of the multicast channel from a channel change server to a set-top box, starting the unicast video stream with a keyframe from the early past of the requested TV channel ,

A disadvantage of the prior art is that either long delay times arise when switching between video signals. The solution of Peter Siebert et al. requires unicast transmission as well as buffering of the multicast stream in a channel change server and yet the delay due to the decode time and time for rearranging the inter-coded frames is not completely minimized.

The object of the present invention is to improve the disadvantages of the prior art. The object is solved by the independent claims. Advantageous developments are defined in the subclaims. In particular, the object is achieved by a transmission method for transmitting a digital, originally inter-coded video signal (11) to a receiving device (20), comprising the following steps, which are carried out in a server (10):

- receiving (200) an access request (300) with respect to the video signal (11);

- transmitting (210) at least one intra-coded frame (52) of a stream (51) of intra-coded frames (52) of the video signal (11). In this way, the server sends to the receiving device, at least in the short term, a stream of intra-coded frames that can be immediately decoded on the receiving device's side without delay because of waiting for a keyframe or waiting for the sequence of frames to reorder.

The digital originally inter-coded, preferably continuous, video signal is preferably a video signal encoded by MPEG standard (MPEG-1, MPEG-2 or MPEG-4) or H.264 standard. It is preferably the digital video signal of a TV provider and / or a computer program

(eg, computer games, collaborative or non-collaborative computer programs, cloud applications such as office, shared word processing on a document, cloud gaming, digital cloud service), preferably a multi-user computer program. The source of this signal is preferably within the range of influence of the TV provider and / or on a program server (eg cloud server) and there, in this source the signal is coded such that different frames are inter coded, ie dependencies are temporally successive. gender frames were considered for compression. Most preferably, the source of the originally inter-coded signal is on the same server on which the inventive method is performed. Preference is originally to be understood in the local sense, ie the signal is inter coded at its place of origin, particularly preferably originally (preferably additionally) in the temporal sense, ie initially or originally (eg at a time t = 0) the signal is inter-coded and over time it is at least temporarily generated (eg at a time t = T, eg during a switching / zapping process or a program update) as an exclusively intra-coded signal and / or sent. For example, the method according to the invention is carried out on the same server and / or a server system accessible to a service provider (eg servers of head stations of one or more cable television networks connected by means of glass fiber, for example), on which digital services (e.g. As cloud applications such as games, office applications, etc., preferably multi-user cloud applications) are offered or hosted with graphical output. For example, the graphical output will be multicast, more preferably unicast (e.g., in games or programs where each user receives his own personal visualization that may differ from the visualization for other users) to the respective user first and / or usually, ie, originally in the temporal sense, as an inter-coded video signal. In the case of updating the visualization (eg, due to switching or program action), the originally inter-coded video signal is now temporarily generated and transmitted as an intra-coded video signal from the respective program. Preferably, as soon as the update or the switching is completed, the original inter coding is switched back.

The receiving device is preferably a set-top box in the sphere of influence of the television viewer or program user and / or a TV tuner or Internet receiver integrated in a television set or connected to a computer and / or a game console or computer, with the or via a network - work (ulti-user) programs are executable. The receiver is particularly preferably a set-top box with (preferably exclusively) one or more components from the set: controller for input devices, network interface, video and / or audio decoder, video and / or audio output controller. In this way, the receiving device is reduced to the essentials, so that by shifting the computing load for computer programs to the server, which is acceptable only by minimizing the delay of the video signal for the user, a very inexpensive receiver device is used.

The server on which the method according to the invention is carried out is preferably a computing unit which is suitable for carrying out a rapid channel change or a rapid updating of the video signal as a function of the

Access request is set up and programmed. The server is preferably within the sphere of influence of the TV and / or program provider, eg. On the one hand, the video signal is encoded on the same server, on the other hand, the transmitting method according to the invention is carried out (for example, in particular in the case of provision of the online execution of a program via a network). Particularly preferred (eg in particular in the case of TV signals) is the server on which the method according to the invention is carried out between the TV and / or program provider or TV and / or program server and the viewer of the viewer lying server, on the one hand receives the video signal from the TV and / or program provider or the server of the TV and / or program provider and further performs the inventive method leads, so that the viewer and / or program users on the receiver then a rapid change of channel or ., a fast update of the video signal or a quick turn on a channel or a fast connection to a running computer program can perform.

A provider is preferably understood to be someone who provides a digital service on a server. In the case of nes TV video signal, it is z. B. the broadcaster (eg.

Pro7), which sends a digital TV signal via a server as stream (eg as Multicaststeram or Broadcasstream). In the case of a video signal of a program, the provider z. For example, an operator of a cloud server or a server that supplies a television cable network with digital IP data, wherein the provider, the online execution of programs (games, office applications, multi-user or single-user cloud applications, etc .) on its server for users and thereby sends the graphic visualization of the respective program as a stream (for example, as unicast or multicast or - less often - as a broadcast stream). In particular for a program provider, the server (complex) on which the respective program is provided for execution is preferably identical to the server (complex) on which the method according to the invention is carried out, since thus the coding () already occurs when the video stream is generated (FIG. Intra- or inter-coding) is set according to the method, so that correspondingly encoded frames can be sent. The video signal from programs is preferably generated in interaction with the user (s). In this way, the server's responsiveness can be leveraged to deliver good results (eg, higher quality images) from user actions at the very moment.

An access request is z. B. pressing a button on the remote control, which generates a particular signal that carries information that either a particular channel is to be turned on or that should be switched from a currently considered video signal to another video signal. In a computer program, the access request is preferably an input action of a user, e.g. B. an operation of an input device (eg., Mouse, joystick, game controller, keyboard, microphone, touchpad, etc.). The access request in this case preferably represents a request for accessing an updated video signal of the program state. This is preferably from any of the participating users. The server preferably receives the access request from the receiving device. The reception takes place z. B. over a cable TV network, Internet and / or over a wireless link. Preferably, the access request includes the instruction of the user to pause or fast forward or rewind the video signal. For this purpose, preferably on the server, the video signal, preferably in a buffer with adjustable buffer size, cached. This is done especially for TV signals. Preferably, such an instruction of the user is received with the access request.

An intra-coded frame (I-frame or K-frame) is preferably a keyframe without information about frames of other times and is already decodable only on its own. It thus carries all the information about decoding in itself. An intra-coded frame is e.g. a keyframe of any of the above codes. Most preferably, it is an MJPEG frame. A stream of intra-coded frames is preferably a data stream consisting exclusively of intra-coded frames. Such a stream is e.g. an MJPEG stream, or an MPEG or H.264 stream, each one exclusively

Keyframes exist, which is also possible with this code (MPEG, H.264), although it is unusual in the state of the art. Preferably, the stream of intra-coded frames has a reduced quality compared to a originally inter-coded video signal, e.g. Due to a reduced resolution or a higher intra-compression of the individual frames, whereby the stream of intra-coded frames is more bandwidth-friendly, than a stream of I-frames with the quality, the z. B. has an I-frame in the originally inter-coded signal. Particularly preferably, the stream of intra-coded frames has the same or higher quality than the inter-coded video signal, eg. B. due to the same or increased resolution and / or increased frame rate. A short-term, higher necessary data tenrate for transmission of the stream accepted. The intra-coded frames are preferably created by the server from the inter-coded frames. Preference is given to a reduction in the quality of the video signal by reducing the resolution and / or frame rate and / or by increasing the data compression, particularly preferably maintaining the quality is made or increasing the quality by z. Inter-frame interpolation and / or pixel interpolation and / or reduction of data compression. The source (eg encoder of the TV provider or encoder of the game server or of the game provider) of the originally inter-coded video signal is particularly preferably instructed to produce a stream of intra-coded frames with preferably reduced, particularly preferably equal or increased quality, preferably as a function of Number of access requests per time, preferably in addition to the stream of inter-coded frames, more preferably instead of the stream of inter-coded frames. So z. B. the encoder of the program, in particular game visualization, upon receipt of an access request (ie, for example, a

Game action) to send a purely intra-coded stream instead of the inter-coded stream. This purely intra-coded stream preferably has a higher frame rate

and / or resolution. In this way, those program / game scenes in which changes by program / game actions are visible, displayed with an increased quality, allowing a smoother and / or more detailed program / game visualization. The transmission preferably takes place via a cable television network, and / or an Internet and / or a radio link to the receiving device. The transmission preferably takes place as a unicast stream, but preferably as a multicast stream. For example, in a computer program, the at least one intra-coded frame of the stream is preferably sent to all receiving devices of the participating users (eg, players) from intra-coded frames. It is advantageous in some programs that send at least one intra-coded frame of the stream as multicast, e.g. For example, if the visualization is identical for all users (eg common word processing, board games such as chess, nibbles, games with splitscreen in which each user follows the screens of the other users etc.), in some programs this is Send as unicast advantageous (eg, individual applications, (3D) games with individual perspective for each user, etc.). An access request of only one user (ie eg a game action of a player) thus preferably causes a transmission to all users, preferably as an IP multicast stream, so that all users receive an updated program visualization without the delay due to the original inter-coding. Particularly preferably, the server calculates which user should / should receive an updated program visualization on the basis of the access request (for example, in some players the visual state does not change despite the game action of a player, since the players each have different video signals for their own receive their own game perspective, in which the action of one player is not visible) and only sends to them.

Preferably, instead of a (further) transmission of the inter-coded video signal, only the stream of intra-coded frames, or the at least one intra-coded frame, is sent as a temporary substitute for the inter-coded video signal. In this way, transmission bandwidth of the server is saved at the moment of switching / updating. In a further transmission method according to the invention

With the transmission (210) of the at least one intra-coded frame (52)

a) transmitting at least one intra-coded frame (52) of the stream (51) of intra-coded frames (52) of the video signal (11) having an increased pixel resolution and / or a lower compression rate than frames of the inter-coded video signal (11); or b) a sequence of intra-coded frames (52) of the video signal (11) is sent, which has a higher frame rate than the interco- decoded video signal (11).

In this way, the above-described increase in the quality of the video when switching or when updating (for example, if it is a video game) is performed. Preferably, the server according to the invention comprises means for performing such quality enhancement (eg, encoder configured to encode higher resolution and / or apply lower frame compression and / or generate a sequence of inktraked images at a higher frame rate and / or interpolation means for inter-frame and / or inter-pixel interpolation).

A further transmission method according to the invention additionally comprises the steps:

- transmitting (220) at least one inter-coded frame of a stream (31) with inter-coded frames of the video signal (11); and preferably the steps:

- determining (230) whether a time period T has elapsed or if there is an acknowledgment message from the receiving device (20);

if a time period T has elapsed or if a confirmation message is present:

- stopping (240) the transmission of the stream (51) from intra-coded frames (52).

In this way, the stream of intra-coded frames is only transmitted until the receiving device can decode the inter-coded frames, preferably the multicast-transmitted video signal. Thus, the bandwidth-intensive stream is sent out of intra-coded frames only for a short time. An inter-coded frame is one that can not be decoded by itself without the knowledge of another frame (eg, a so-called B-frame or P-frame). The stream from in- The coded frame preferably also contains intra-coded frames (eg so-called I-frames or K-frames or also keyframes) at specific intervals. The time period T is preferably an empirically determined

Time. Particularly preferably, the time T is fixed and amounts to the double, preferably simple time equivalent of a so-called "group of pictures (GoP)" _f, ie a group of frames which is decodable independently of another group of frames. Particularly preferably, the time T is dependent on the time at which the access request is received and the state of the multicast stream, with inter-coded pictures. If the access request z. B. is received shortly after the time at which a K-frame was received via the multicast stream of the TV and / or program provider, the time T is longer than if the

Access request is received just before the next K-frame of the TV provider is expected. The confirmation message from the receiving device is preferably an OK note with which the receiving device signals that now no intra-coded frames are more necessary, since it was already possible to successfully switch to the multicast stream with the inter-coded frames. Preferably, with the stream with inter-coded frames or with the stream of intra-coded frames, an associated soundtrack is also sent. If, in a computer program, intra-coded frames are sent to a plurality of users, the acknowledgment message triggering the stopping of the transmission of the at least one intra-coded frame or the stream of intra-coded frames is the last incoming acknowledgment message of the users. Preferably, acknowledgment messages are provided with information relating the acknowledgment message to an already received access request. The server preferably determines which access request is acknowledged and continues to send intra-coded frames if for at least one access request. confirmation is not present, preferably if in addition a time T has not expired.

A further transmission method according to the invention additionally comprises the step:

- decoding the at least one inter-coded frame of the stream (31) with inter-coded frames of the video signal (11) to at least one intra-coded frame (52). In this way, a stream consisting of intra-coded frames is created from the multicast stream received from the TV and / or program provider. The decoding preferably also includes an encoding, z. In an MJPEG format or an MPEG or H.264 format with only K-frames. The decoding preferably also includes subsampling with regard to the frame sequence and / or the frame pixels and / or a compression gain to reduce the quality. It particularly preferably includes an interpolation (upsampling) with regard to the frame sequence and / or the frame pixels and / or a compression reduction. Preferably, the reduction and / or increase in quality is preferably carried out depending on the bandwidth currently available in the network. For example, if there is too little bandwidth available at the moment, the quality of the intra-coded frames is further reduced or correspondingly reversed. Preferably, an increase in quality is performed in computer programs. Preferably, this increase is dependent on the number of access requests occurring per time (eg, the more requests, the higher the quality, or the quality is increased only with a minimum number of requests). Thus, program scenes with many program actions are presented in a more fluid and / or more detailed manner.

Caching of the at least one inter-coded frame of the stream (31) with inter-coded frames of the video signal nals (11) into a buffer;

- Reading a bridging sequence (33) with inter-coded frames from the buffer, wherein the bridging sequence (33) starts with an intra-coded frame.

- Sending (221) the bridging sequence (33) by means of a burst transmission over a unicast connection to the receiving device (20).

In this way, a reduction of the bandwidth required in the switching is achieved because the bridging sequence, which consists mainly of inter-coded frames, a portion of the switching delay is bridged and the other part of the switching delay, even in the bridging sequence due to the decoding and reordering yet is necessary is, by the inventive shipment of the

Bridges streams from intra-coded frames.

The server preferably has an intermediate memory which holds at least two GoPs of the inter-coded video signal.

Preferably, the bridging sequence analogous to the preferred or particularly preferred embodiment of the intra-coded frames has a reduced or increased quality, eg. B. due to a reduced or increased resolution (with respect. Image rate and / or pixel resolution) or a higher or lower intra-compression of the individual frames on, with particularly preferred quality depending on the currently available bandwidth and / or a rate of access requests per time is chosen.

Burst transmission uses higher bandwidth compared to normal video transmission, but only for a short time, and thus shortens the time normally required to transmit a certain number of frames. In a further transmission method according to the invention, the following step is performed first:

- Sending (250) at least one inter-coded frame of a stream (31) with inter-coded frames of another, previously requested video signal (12).

In this way, the method according to the invention can be integrated into a switching process of a television channel and / or updating process of a computer program by first transmitting the video signal of one channel and / or program visualization state and then to another channel or program visualization state by means of the aforementioned steps is switched. The object is furthermore achieved, in particular, by a receiving method for delay-receiving a digital, originally inter-coded video signal (11) from a server (10), comprising the following steps, which are carried out in a receiving device (20):

- receiving (100) an access request (300) with respect to the video signal (11);

- Sending (110) the access request (300) to the server

(10);

Receiving (120) at least one intra-coded frame (52) of a stream (51) of intra-coded frames of the video signal

(11) from the server (10);

- decoding (130) the at least one intra-coded frame (52) to at least one image frame (21);

Displaying (140) the at least one decoded image frame (21) from the stream (51) of intra-coded frames.

In this way, z. B. in a power-on or switching operation due to the additionally encoded to the original inter-coded video signal intra-coded frames, a minimization of the switching or switch-on delay and / or update delay possible. The receiving device does not need to receive a minimum number of inter-coded frames but decodes the received intra-coded frames immediately without the presence of another frame and displays them to the viewer. The receiving device receives the access request z. B. from a remote control, a keystroke on a keyboard o- an operating element of the receiving device or an input device for it. The sending to and receiving from the server preferably takes place via a cable television network, particularly preferably the Internet and / or a radio link.

In a further reception method according to the invention, the reception of (120) the at least one intra-coded frame (52)

a) receiving at least one intra-coded frame (52) of the stream (51) from intra-coded frames (52) of the video signal (11) having an increased pixel resolution and / or a lower compression rate than frames of the inter-coded video signal (11) and / or

b) receive a sequence of intra-coded frames (52) of the video signal (11) having a higher frame rate than the inter-coded video signal (11).

In this way, an increase in video quality when switching / updating is performed. The receiving device preferably has means to receive and / or process for the display such intra-coded frames or a sequence of such frames which have a correspondingly increased quality (pixel resolution, low compression rate, higher frame rate).

A further receiving method according to the invention additionally comprises the steps:

- Receiving (150) at least one inter-coded frame of a stream (31) with inter-coded frames of the video signal (11) from the server (10) and preferably storing the at least one inter-coded frame in a video buffer (30);

- determining (160) whether there are sufficient inter-coded frames for decoding;

if there are enough inter-coded frames for decoding, additionally comprising the steps:

- decoding (170) the existing inter-coded frames into image frames (21);

Displaying (180) the decoded image frames (21) from the stream (31) with inter-coded frames

and preferred

- Sending a confirmation message to the server (10).

In this way, the receiving device receives the multi (or broadcast or un) cast stream of the TV and / or program provider and the normal process of preparing the display of the image frames from this multicast stream, including pre-buffering and decoding, as soon as sufficient frames are available in the Buffer is started. Preferably, in this way, the display of the image frames decoded from the stream of intra-coded frames seamlessly switches over to the display of the decoded image frames from the stream with inter-coded image frames. The detection is preferably a check of the fill level of the video buffer. The required fill level of the video buffer is preferably dependent on the respective coding mode.

An image frame is preferably a frame, which is prepared in such a way that it can be displayed on the screen or on a display device. Preferably, with the at least one inter-coded frame or with the at least one intra-coded frame, an associated sound track is received which can be played without delay. The soundtrack is preferably added to the display of the image frames from the intra-coded frames and played out together. A further receiving method according to the invention additionally comprises the steps:

- Receiving a bridge sequence (33) with inter-coded frames by means of a burst transmission over a unicast connection to the server (10), wherein the bridging sequence (33) starts with an intra-coded frame;

- storing (152) the bridging sequence (33) with inter-coded frames in the video buffer (30). In this way, the video buffer is filled faster due to the burst transmission, and it can be switched even earlier to the normal desired decoding of the inter-coded video signal. In a further reception method according to the invention, the following step is performed first:

- Displaying (190) at least one image frame (21) of another, previously requested video signal (12). In this way, the method is preferably integrated into a switching operation and / or updating process of a program by first the video signal of a first television channel or a first program state is displayed and then with the aid of the inventive method steps at the end of the video signal of another TV channel and / or updated program state that was switched to or updated.

The object is furthermore achieved, in particular, by a receiving device (20) for delay-receiving a digital, originally inter-coded video signal (11) from a server (10) comprising at least one video decoder (50), at least one video buffer (30) a first input of the video decoder (50) is connected, wherein the receiving device (20) comprises means (80) for transmitting a

Access request (300) with respect to the video signal (11) to the server (10) and the video decoder (50) has a second input (56) for receiving intra-coded frames (52) of a stream (51) of intra-coded frames (52).

In this way, with the receiving device, the receiving method according to the invention can be carried out. Due to the second input of the video decoder, received intra-coded frames are passed directly to the video decoder without first having to travel through the normal video buffer necessary for inter-coded frames. However, the receiving device preferably has a buffer to compensate for network delay or constant or variable bit rates. Such a buffer preferably also passes through the intra-coded frames.

The decoder preferably has a chip internally. Depending on the internal connection of the inputs to the chip, the chip preferably decodes frames from the first input or from the second input. More preferably, the video decoder internally has an additional separate chip which decodes the intra-coded frames supplied via the second input, and the first chip decodes the frames supplied via the first input.

Preferably, the receiving device is configured to receive a stream of intra-coded frames of the video signal and a stream of inter-coded frames of the video signal in parallel.

In a further embodiment of the receiving device (20) according to the invention, the latter comprises a device for determining the decodability of inter-coded frames in the video buffer (30).

Such a device is z. B. a level checking unit of the video buffer. This is particularly preferably a logic that checks whether all the necessary for the decoding of the last arrived frame in the video buffer Frames are present in the video buffer.

In a further embodiment of the receiving device (20) according to the invention, the device (80) for sending an access request (300) is additionally configured to send an acknowledgment message to the server (10) as soon as frames with inter-coded frames are decodable in the video buffer (30) , For this purpose, the receiving device preferably has a return channel to the server.

The object is furthermore achieved, in particular, by a server (10) for transmitting a digital, originally intercoordinated video signal (11) to a receiving device (20), the server (10) having at least one device (90) for receiving an access request (300 ) and at least one means (45) for transmitting at least one intra-coded frame (52) of a stream (51) of intra-coded frames (52) of the video signal (11).

In this way, an access request for a particular video signal z. B. a TV channel and / or an updated program state by the server and then a stream of intra-coded frames can be sent.

The device for transmitting at least one intra-coded frame is z. B. a device which processes the intra-coded frames for the network in a certain way z. For example, to not exceed a certain bit rate (buffers) or to comply with certain protocol or coding conventions.

The access information preferably contains the information as to which channel or video signal is requested. loading The access request preferably also contains the information about which receiving device has sent the access request. In the second case, statistics about the viewing habits of the users of a respective receiving device can be created.

In a further embodiment of the server (10) according to the invention, the latter additionally comprises at least one video decoder (40) with a video buffer (30), the video decoder (40) having means (45) for transmitting at least one intra-coded frame (52) of a stream ( 51) is connected from intra-coded frames (52).

In this way, the multicast stream received from the TV and / or program provider is one of intra-coded

Frames of existing stream can be created. In this case, the original data of the TV and / or program provider arriving in the server (with inter-coded frames) can be stored in the video buffer. The video buffer is preferably so large that two GoPs can be stored in the video buffer. Preferably, the server also has a buffer downstream of the decoder for MJPEG or intra-coded frames. This buffer is preferably so large that so many intra-coded frames can be stored there as well as having two GoPs of the intercoded video signal.

In a further embodiment of the server (10) according to the invention, the device (90) for receiving a

Access request (300) is additionally configured to receive an acknowledgment message from the receiving device (20) and / or determine the expiration of a period T.

In a further embodiment of the server (10) according to the invention, the server (10) is arranged in a cable head station (60). In this way, users who are in a tree of a cable TV network about z. B. IP television and / or network programs have, by means of such a server quickly aufschaltbar on a particular video signal or switchable between two different video signals and / or updated versions of video signals, without causing large delay times are visible to the user.

In a further embodiment of the inventive server (10) or the receiving device (20) according to the invention, the server (10) and the receiving device (20) are connected via a coaxial cable network (70).

The invention will now be further illustrated by way of example with reference to the drawings. 1 shows an overview of a transmission method according to the invention,

an overview of a receiving method according to the invention,

a representation of a server according to the invention and receiving devices according to the invention in the state of receiving a previous video signal before a switching operation,

a representation of a server according to the invention and receiving devices according to the invention in the state of receiving a stream of intra-coded frames of the requested video signal during the switching operation,

a representation of a server according to the invention and receiving devices according to the invention in the state of receiving the stream of inter-coded frames of the requested video signal after the switching operation,

a scheme of a switching operation without measures for reducing the switching delay, Figure 5 is a schematic of a switching operation using the inventive transmission and reception methods

FIG. 6 shows a diagram of a switching process using the transmission and reception methods according to the invention, wherein in addition a bridging sequence is transmitted and received.

FIG. 1 shows an overview of a transmission method according to the invention.

In a first step 200, an access request is received by a receiving device, then is in a

Step 210 sends a sequence 51 of intra-coded frames 52 of the requested video signal 11 to the receiving device. In this example, sending is done as multicast.

Optional steps or components are shown dotted. In another embodiment of the invention, parallel to the transmission of the intra-coded frames 52, a stream 31 of inter-coded frames corresponding to that of the TV and / or program provider is multicast to the receiving device in this example. In a step 230, it is then checked whether a certain time T has elapsed or whether an acknowledgment message is available from the receiving device. If this is not the case, the

Step 210 repeats and continues to send intra-coded frames 52 to the receiving device. If a time T has expired or an acknowledgment message is present, the transmission of the intra-coded frames 52 is stopped in a step 240.

In this way, in response to a channel request, intra-coded frames are sent to a receiving device, so that this receiving device can begin decoding and displaying the requested video signal without decoding delay or delay due to waiting for a key frame. Once the receiving device receives an indication due to the inter-coding This is signaled via a confirmation message from the receiving device 20 or this is estimated over a time T and then then the transmission of the intra-coded frames is set again.

In step 250, another previously requested video signal is displayed. This step would therefore be assumed to be switched from another, previously requested video signal to a new video signal 11.

FIG. 2 shows an overview of a receiving method according to the invention. In a step 100, an access request 300 relating to a new video signal 11 is received from the user of the receiving device 20. In a step 110, this access request 300 is forwarded to the server 10. In step 120, the sequence 51 of intra-coded frames 52 of the video signal 11 is then received by the server 10. In step 130, the intra-coded frames 52 are decoded to image frames 21, which are then displayed in step 140.

In this way, the receiving device 20 receives after a

Access request 300 immediately a set of instantaneously decodable frames 52, which is why the video signal 11 with little delay on the receiving device 20 can be displayed shortly after the occurrence of the access request 300.

In another embodiment of the invention, in step 150, a stream 31 of inter-coded frames of the video signal 11 is received by the server 10. This stream 31 is z. B. the forwarded multicast stream of the TV and / or program provider. In a step 160, it is determined whether there are enough inter-coded frames for decoding. If not, step 150 is repeated and at least one more inter-frame is received by server 10. If the number of inter-coded frames is sufficient, in one step 170 decoding the inter-coded frames into image frames 21, and the image frames 21 decoded from the stream 31 are displayed to the user of the receiving device 20 in a step 180.

In this way, after a certain time and as soon as there are enough frames to represent the video signal 11 by interframed frames received, the video signal 11 is also represented by inter-coded frames. Thus, a bandwidth-conserving representation of the video signal 11 can be switched over after a certain time and the intra-coded frames 52 no longer have to be sent by the server 10. In a step 190, another video signal is previously presented to the user of the receiving device 20. In this case, by carrying out the method according to the invention then switching over with a very short time delay becomes possible.

FIG. 3a shows an illustration of a server 10 according to the invention and receiving devices 20, 20 'according to the invention in the state of receiving a previous video signal before a switching operation by receiving device 20'. In this example, the server 10 is located in the headend 60 of a cable television network 70. For each channel for which fast switching is offered, means 45.1 and 45.2, respectively, are for transmitting at least one intra-coded frame of a stream of intra-coded frames the respective video signal available. In addition, the server 10 includes means 90 for receiving an access request 300 for a video signal. In this example, the server additionally additionally has video buffers 30.1, 30.2 and decoders 40.1, 40.2. Receiving devices 20, 20 'are connected to the server via a coaxial cable network 70. Each receiving device 20, 20 'has a device 80, 80' for sending a channel request 300 to the server 10 on. Each receiving device 20, 20 'also has a video buffer 30, 30' and a video decoder 50, 50 'with a first input 55, 55 ^' and a second input 56, 56 '. In operation of the invention, the receiving device 20 'receives the multicast stream 31.2 the video signal previously requested and stores it in the video buffer 30'. It is then delayed by the size of the video buffer 30 'and fed via the first decoder input 55' the decoder 50 'and decoded there. The same is done for another receiver 20 and the inter-coded stream 31.1 of another video signal. The stream 31.1 is buffered in the video buffer 30.1 in the server 10 and then supplied to a video decoder 40.1 which decodes the inter-coded frames into intra-coded frames, and forwarded to means 45.1 for transmitting at least one intra-coded frame of a stream of intra-coded frames of the video signal , The user of the receiving device 20 'now wants to switch to the video signal which also the receiving device 20 receives via the stream 31. 1 and sends via the device 80 ^' a channel request 300 to the server 10, which receives it by the device 90.

3 b shows a representation of a server 10 according to the invention and receiving devices 20, 20 ^" according to the invention in the state of receiving a stream of intra-coded frames of the requested video signal during the switching operation In the receiving device 20 ', the stream 51 is transferred via the second decoder input 56' to the decoder 50 'and decodes it without waiting for an I-frame or waiting upon filling a video decoding buffer, the received intra-coded frames are displayed to the user of the receiving device 20 'without great delay Server 10 forwarded stream 31.1 with inter-coded frames of the requested video signal and stores it in the video buffer 30 'so that it gradually fills. FIG. 3c shows an illustration of a server 10 according to the invention and receiving devices 20, 20 'according to the invention in the state of receiving the stream from inter-coded frames of the requested video signal after the switching operation. As soon as sufficient frames for decoding are present in the video buffer 30 'of the receiving device 20', these are forwarded to the decoder 50 'via the first decoder input 55' so that these are then decoded. The receiving device 20 'preferably signals to the server 10 via the device 80' that there are sufficient frames of the stream 31.1 from intercoordinated frames, and thus no more intra-coded frames are required. Thereafter, or due to the elapse of a predetermined time T, the transmission of the intra-coded frames by the server 10 is stopped. In this way, a higher bandwidth is required only temporarily for transmitting the intra-coded frames and it can be used after switching or the switch on the normal bandwidth-saving multicast stream of the video signal. However, as a great advantage, the user of the receiving device 20 'experiences no visible delay in the display of the requested video signal in this example.

Figure 4 shows a scheme of a switching operation without measures to reduce the switching delay. In a first state (encircled "1") in a receiving device 20, the decoded image frames 21 originating from a stream with inter-coded frames of a previously requested video signal 12, in this case z. TV channel "17" is displayed to the user in a step 190. In a step 121, this channel "17" is then left and it should be switched to the channel "8", that is, the video signal 11. When you exit channel "17", the display of the image query stops. with the channel "17" and after a user and network delay, waiting for an I-frame of the stream 31 or 31.1 starts with the inter-coded frames. As soon as an I-frame occurs, the receiving device 20 starts to store the interframe frames in the video buffer 30 of the receiving device 20 (step 151). Depending on the type of coding and sequence of the frames, in the worst case a whole group of pictures must be stored in the video buffer 30 of the receiving device 20, which leads to a delay 313 in the worst case. Only then can a display of the decoded image frames 21 take place and these are then displayed to the user in a step 140, whereby state 2 (circled "2") is reached. With this method, where no action is taken to reduce the blackout between switching from one channel to another, an overall switch delay 310 occurs of more than one group of pictures, in the worst case about 2000 ms. The users and network delay 311 is based, for. On packet loss, jitter ping times, users etc.

Figure 5 shows a schematic of a switching operation using the transmission and reception methods according to the invention. The starting point is in turn the state indicated by the encircled "1" as well as in FIG. 4. At least one intra-coded frame 52 of the requested video signal 11 is held in the server 10 at any given time. This is created from the stream 31 or 31.1 of the video signal 11, for which reason the intra-coded frames 52 of the stream 51 are shown delayed by the worst-case decoding delay 313. Upon expiration of a user and network delay 311, the first intra-coded frame 52 is sent to the receiving device 20. There, this is decoded after a decoder delay 314 in the case of an intra-coded frame 52 and displayed. Thus, the system is in the state "2" (encircled "2") in which the user decoded image frames 21 ange- which originate from a stream 51 of intra-coded frames 52. In parallel, the receiving device 20 stores inter-coded frames into a video buffer 30 in a step 151. Once there are enough inter-coded frames (indicated by a decode delay 313), the decoding of the inter-coded frames starts, which are then displayed instead of the decoded image frames from the stream 51. Stream 51 is then no longer necessary and will be turned off. This puts the system in state "3" (encircled "3").

By using this method, the total switch delay 310 is minimized to a maximum delay of only two frames (about 80 ms). No matter at which point the user switches from one channel to the other channel, this time delay is minimized (random zapping).

FIG. 6 shows a diagram of a switching process using the transmission and reception methods according to the invention, wherein in addition a bridging sequence 33 is transmitted and received. After leaving the channel "17", the transmission of intra-coded frames 52 of a stream 51 takes place again. In addition, the video buffer is filled faster than normal via a burst transmission with a bridging frequency 33, in this case a complete group of pictures (step 152 ). Alternatively or in combination, the fast filling of the video buffer in step 152 is also due to a reduced quality and thus a reduced data volume of the bridging sequence 33. The decoding delay 313.1 of the bridging sequence 33 is shortened compared to the decoding delay of a normal transmitted sequence of inter-coded pictures the bridging sequence 33 arrives faster in the buffer of the receiving device 20. However, even during this shortened decoding delay 313.1, the decoded image frames 21 are already removed from the

Stream 51 is displayed from intra-coded frames 52. Once the bridging sequence 33 is present in the video buffer and decoded bar, it is decoded and displayed to the user. From this moment on, the transmission of the stream 51 from intra-coded frames 52 is no longer necessary, since it is now possible to decode and display solely on the basis of the inter-coded frames.

The switching delay 310 is also a maximum of only two frames (about 80 ms), however, the stream 51 is not sent from intra-coded frames 52 for such a long duration as in the example of Figure 5. For this reason, the operations of switching can be reduced to an even shorter period of time.

With this invention, methods have been presented, such as a server and a receiving device, with the help of which the turn-on and switching delay in digital video signals in particular digital television signals and / or program video signals reduced to a minimum. On the side of the receiving device, means for interacting with the server sending the video signals are provided. The server then reacts on the basis of a channel request and / or update request preferably by sending not only interframed frames but also, in parallel or preferably, inter-coded frames to the receiving device instead of the inter-coded frames. While the receiving device also buffers the inter-coded pictures as in the prior art, an image for the display can already be created after the much shorter time span of the decoder of the intra-coded frames and therefore with a minimum delay after the channel request. It is only for a short

Time required a higher bandwidth because the receiving device, as soon as enough inter-coded frames have been stored, they can then decode and display and is no longer dependent on the intra-coded, additionally sent frames. A confirmation message informs the server that the stream of intra-coded frames is no longer to be sent. By the statistical distribution During the switching times and / or program update times of many different users, the higher bandwidth occupancy during switching and / or updating will not, on average, result in any grossly increased bandwidth requirements for the particular channel. The combination with the transmission of a bridging sequence additionally shortens the time required for the transmission of the intra-coded frames, so that the switching and / or updating requires even less additional bandwidth and, overall, all the necessary operations are completed within an even shorter time ,

reference numeral

10 servers

11 video signal

12 Other, previously requested video signal

20 receiving device

21 picture frame

30 video buffers

31 stream with inter-coded frames

31.1 Multicast Master Stream with inter-coded frames of the video signal

31.2 Multicast Master Stream with inter-coded frames of another previously requested video signal

32 Intra-coded frame

33 bridging sequence

33.1 Group of Pictures

40 video decoder of the server

45 means for transmitting at least one intra-coded frame of a stream of intra-coded frames of the video signal

50 video decoder of the receiving device

51 Stream of intra-coded frames

52 Intra-coded frame

52.2 Lost intra-coded frame

55 First entrance

56 Second entrance

60 head station

70 coaxial cable network

80 Device for sending an access request

90 means for receiving an access request

100 receiving an access request for the video signal

110 Send the access request to a server

120 receiving at least one intra-coded frame of a stream of intra-coded frames of the video signal from the server Leaving another, previously requested video signal

Decoding the at least one intra-coded frame to at least one image frame

Connecting to the video signal over the stream with inter-coded frames

Connecting to the video signal over the stream of intra-coded frames

Display the at least one decoded image frame from the stream of intra-coded frames

Receive an inter-coded frame of a stream with inter-coded frames of the video signal

Storing inter-coded frames in the video buffer

Save the bypass sequence to the video buffer

Determine if there are enough inter-coded frames for decoding

Decode the existing inter-coded frames to image frames

Display the decoded image frames from the stream with inter-coded frames

Displaying at least one decoded frame of another previously requested video signal

Receiving an access request for the video signal

Transmitting at least one intra-coded frame of a stream of intra-coded frames of the video signal

Transmitting at least one inter-coded frame of a stream with inter-coded frames of the video signal

Sending a bridge sequence with inter-coded frames using a burst transmission over a Unicast connection

Determine if a time T has expired or if there is an acknowledgment message from the receiver of the stream of intra-coded frames

Stop sending the stream out of intra-coded frames Transmitting at least one inter-coded frame of a stream with inter-coded frames of another previously requested video signal

access request

switching delay

User and network delay

Delay waiting for an intra-coded frame of a stream with inter-coded frames and decoding time

Decoding delay in the worst case

Decoding delay of the bridging sequence

Decoding delay in the case of an intra-coded frame

Claims

claims

A transmission method for transmitting a digital, originally inter-coded video signal (11) to a receiving device (20), comprising the following steps performed in a server (10):

- transmitting (210) at least one intra-coded frame (52) of a stream (51) of intra-coded frames (52) of the video signal (11).

2. A transmission method according to claim 1, wherein

with the transmission (210) of the at least one intra-coded frame (52)

a) at least one intra-coded frame (52) of the stream (51) is sent from intra-coded frames (52) of the video signal (11) having an increased pixel resolution and / or a lower compression rate than frames of the inter-coded video signal (11) and / or

b) sending a sequence of intra-coded frames (52) of the video signal (11) having a higher frame rate than the inter-coded video signal (11).

3. Transmitting method according to one of the preceding claims, additionally comprising the steps:

- transmitting (220) at least one inter-coded frame of a stream (31) with inter-coded frames of the video signal (11);

and preferably the steps:

if a time period T has expired or if a confirmation message is present:

Stopping (240) the transmission of the stream (51) from intraco- diert frames (52).

4. Transmission method according to one of the preceding claims, additionally comprising the step:

- decoding the at least one inter-coded frame of the stream (31) with inter-coded frames of the video signal (11) to at least one intra-coded frame (52).

5. Transmitting method according to one of the preceding claims, additionally comprising the steps:

- Latching the at least one inter-coded frame of the stream (31) with inter-coded frames of the video signal Vi (11) in a buffer memory;

- Sending (221) the bridging sequence (33) with interko-based frames by means of a burst transmission over a unicast connection to the receiving device (20).

6. A transmission method according to any one of the preceding claims, wherein first the following step is performed:

- transmitting (250) at least one inter-coded frame of a stream (31) with inter-coded frames of another previously requested video signal (12).

A receiving method for delay-receiving a digital, originally inter-coded video signal (11) from a server (10), comprising the following steps performed in a receiving device (20):

- sending (110) the access request (300) to the server (10);

Receiving (120) at least one intra-coded frame (52) of a stream (51) of intra-coded frames of Vi deosignals (11) from the server (10);

- displaying (140) the at least one decoded one

Image frames (21) from the stream (51) of intra-coded frames.

8. receiving method according to claim 7, wherein

with receiving (120) the at least one intra-coded frame (52)

a) at least one intra-coded frame (52) of the stream (51) is received from intra-coded frames (52) of the video signal (11) having an increased pixel resolution and / or a lower compression rate than frames of the inter-coded video signal (11); /or

b) receiving a sequence of intra-coded frames (52) of the video signal (11) having a higher frame rate than the inter-coded video signal (11).

9. receiving method according to claim 7 to 8, additionally comprising the steps:

- decoding (170) the existing inter-coded frames into image frames (21);

and preferred

- Sending a confirmation message to the server (10). Receiving method according to claims 7 to 9,

additionally comprising the steps:

- Receiving a bridging sequence (33) with inter-coded frames by means of a burst transmission via a unicast connection to the server (10), wherein the bridging sequence (33) starts with an intra-coded frame.

- storing (152) the bridging sequence (33) in the video buffer (30).

A receiving method according to any one of claims 7 to 10, wherein first the following step is performed:

- Displaying (190) at least one image frame (21) of another, previously requested video signal (12).

Receiving device (20) for delay-receiving a digital, originally inter-coded video signal (11) from a server (10),

comprising at least one video decoder (50), at least one video buffer (30) connected to a first input of the video decoder (50),

characterized in that

the receiving device (20) has a device (80) for sending an access request (300) with respect to the video signal (11) to the server (10), and the video decoder (50) has a second input (56) for receiving intra-coded frames (52 ) of a stream (51) of intra-coded frames (52).

Receiver (20) according to claim 12,

additionally comprising means for determining the decodability of inter-coded frames in the video buffer (30).

The receiving device (20) according to any one of claims 12 to 13, wherein the means (80) for sending an access request (300) is additionally set up, a Bestä- send message to the server (10) as soon as frames with inter-coded frames in the video buffer (30) are decodable.

15. Server (10) for transmitting a digital, originally inter-coded video signal (11) to a receiving device (20), characterized in that

the server (10) comprises at least one device (90) for receiving an access request (300) for the video signal (11) and at least one device (45) for transmitting at least one intra-coded frame (52) of a stream (51) of intra-coded frames ( 52) of the video signal (11).

16. server (10) according to claim 15,

additionally comprising at least one video decoder (40) with a video buffer (30), the video decoder (40) being connected to the means (45) for transmitting at least one intra-coded frame (52) of a stream (51) of intra-coded frames (52).

17. Server (10) according to claim 15 to 16,

wherein the means (90) for receiving an access request (300) is additionally arranged to receive an acknowledgment message from the receiving device (20) and / or to detect the expiration of a time period T.

The server (10) of claims 15 to 17, wherein the server (10) is located in a cable head station (60).

19. Server (10) according to claim 15 to 18 or receiver (20) according to claim 12 to 14,

wherein the server (10) and the receiving device (20) are connected via a coaxial cable network (70).