WO2009018791A1

WO2009018791A1 - Method and system for reducing the switching gap during a program change in a digital video environment

Info

Publication number: WO2009018791A1
Application number: PCT/DE2008/000064
Authority: WO
Inventors: Alexander Stumpf; Heiko Dassow; Torsten Orth
Original assignee: Deutsche Telekom Ag
Priority date: 2007-08-07
Filing date: 2008-01-16
Publication date: 2009-02-12
Also published as: DE112008002798A5; EP2177032A1

Abstract

The invention relates to a method and to a data transmission system (10) for reducing the switching gap occurring in a terminal (160) when switching from a digital video data stream of a first program to a digital video data stream of a second program. The present invention is based on the aim of minimizing this switching gap. To this end, the video information of a program to be transmitted is distributed in an encoding device (30, 31, 32) to a plurality of parallel, preferably multi-cast, streams and transmitted to at least one distribution point (90) via an IP-based distribution network (60). If a receiver device (120), particularly a set-top box, installed at the user has the necessary knowledge when frames are present in the parallel multicast streams, and optionally how a plurality of multicast streams received can be put together, the time of illustration of the first frame of the new program on a terminal (160) associated with the receiving device (120) can be optimized such that the resulting switching gap can be minimized when changing programs.

Description

Method and system for reducing the

Switchover gap during a program change in a digital video environment

description

The invention generally relates to a video or multimedia network environment for distributing programs to a plurality of subscribers, and more particularly to a method and a data transfer system for reducing the switching gap when switching from a first program to a second program.

Methods and systems for the transmission of group-specific Medienstrδmen, also called media streams, via a distribution network are well known. In these known methods, various media streams are fed into the distribution network at one or more predetermined points, and at the other end of the distribution network via so-called multicast.

Replication points targeted to individual participants or groups of participants fed.

An essential aspect of such multimedia communication systems is to provide measures to enable a switchover from one program channel to another program channel. In this case, the problem often arises that when switching between two program channels, a visible disturbance in the visualized content is perceived by the subscriber. Because when switching between channels at any time is not guaranteed that after switching a seamless transmission of the destination channel or an immediate playback of the destination channel at the subscriber is possible. Basically, when switching from a currently displayed program to a new program, it must be ensured that a full screen is sent at the beginning of the presentation of the new program, so that a continuous, seamless image structure after the

Switching process is made possible and thus visible interference to the subscriber can be avoided.

A known method for seamless switching between program channels in a digital video-based entertainment network is known, for example, from US 2004/0034864 A1. It discloses a system for transmitting digital video signals having a headend having, inter alia, an encoder, means for recognizing and evaluating handoff messages, and means for generating frames. The headend is over a distribution network with a subscriber side Terminal connected. A subscriber initiates a channel change by entering at his terminal a corresponding channel change command which is transmitted over the network to the headend. Under evaluation of the channel change message, the headend recognizer causes the encoder to generate an I frame, that is, a frame of the new destination channel. The full screen of the new destination channel is then transmitted to the subscriber's terminal. In other words, the actual switching between program channels takes place in the coder of the headend. When playing digital audiovisual

Data streams can not be switched from one program to another at any time. This has technical reasons. For example, when the program is switched to video data, it is necessary to wait for the next frame to start the presentation of the new program. The MPEG encoding standard is the currently displayed on the TV program in the set-top box 120 arranged. The video data stored in the memory 132 is transferred to a decoder 142, the video data stored in the buffer 131 is transferred to a decoder 141 and stored in the buffer 130

Video data is decoded in a decoder 142. The decoders 140 through 142 are connected to a switching device 150 which, under the control of a microprocessor 155, can supply a selectable decoded video data stream to the television receiver 160. The selection of the video data stream is under the condition that the switching gap is minimized when changing programs. The microprocessor 155 takes control of the set-top box 120. As will be explained in more detail below, the microprocessor 155 also ensures that the set-top box 120 selects only certain video data streams at the multicast replication point 90, i. H. requests. Optionally, or in addition, the set-top box 120 may also include a mixer 170 which, under the control of the microprocessor 155, may suitably mix decoded video data streams. In the present example, the decoders 140 and

141 connected to the mixer 170. The composite signal is then output from mixer 170 via one of decoders 140, 141,

142 or a separate decoder supplied to the television receiver 160. As mentioned earlier, the set-top box shows

120 only the receiving stage for parallel video data streams of a program. In the event that the set-top box 120 concurrently several programs, d. H. whose associated video data streams should receive, further, similarly constructed receiving stages are to be implemented.

The operation of the data transmission system shown in Fig. 1 will now be explained in detail. For all the scenarios described below, it is assumed that the program 1 of the broadcaster 20 is currently displayed on the television receiver 160.

First embodiment

It is assumed that the user of the set-top box 120 wants to make a program change, namely from program 1 to program 2.

It is further assumed that the coding device 31 encodes the video signal coming from the broadcasting station 21 into four parallel video data streams having the same bandwidth. The four video streams (labeled streams 1, 2, 3 and 4) are shown in FIG. Everyone coded

For example, video data stream is encoded according to the MPEG standard and has regularly recurring frames, also called I frames, labeled I _t in FIG. Furthermore, each video stream transmits so-called P-frames, each containing the image information different from the previous frame. Moreover, in each of the parallel video streams, one frame is simultaneously inserted when a scene change occurs within the program. This frame is indicated in Fig. 5 with I _c . It should be noted at this point that the data structure shown in FIG. 5 has been selected only as an example. Encoder 31 ensures that the frames designated I _t in the four video data streams are offset in time relative to each other. The times to which in each

Video data stream is a frame I _t transmitted, the set-top box 120 must be known. For example, 120 ^• knows the set-top box the algorithm by which the encoder of the Encoder 31 insert frames I _t in the respective video data stream. In this way, as will be explained below, the microprocessor 155 of the set-top box 120 can determine the video stream suitable for minimizing the switching gap. Another possibility is to refer the times at which frames I _t are inserted into the respective video data streams to a reference point which is communicated to the set-top box 120. The reference point may be provided by a central clock or by synchronized clocks implemented in the encoders and the set-top box 120, respectively. The relative times at which frames I _t are inserted into the four video streams may then be within the video streams themselves or in a separate one

Information channel from the encoder 31 via the IP distribution network to the set-top box 120 are transmitted. The differently coded video data streams of the program 2 make it possible to minimize the waiting time until the first displayable frame of the program 2 and thus the switching gap. The video data streams encoded by the encoder 31, which represent the program 2, are transmitted via the IP distribution network 60 to the multicast replication point 90. Now suppose that the user has input to the set-top box 120 a toggle command to change from program 1 to program 2. Thereafter, the set-top box 120 causes the multicast replication point 90 to no longer transmit the video stream associated with the program 1. At this moment, a switching gap appears on the television receiver 160, which must be minimized. The microprocessor 155 knows the timing of the frames I _t within the four parallel ones Video data streams representing the program 2 and the switching time defined by the switching command. In response to this information, the microprocessor 155 at the multicast replication point 90 selects the video stream of the program 2 which next transmits a frame I _t . In this example, the video stream Stream 1 is selected. As soon as at least the video data representing the first frame I _{t is} stored in the buffer 132, the decoder 142 decodes the video data stored in the buffer 132 and passes it on to the television receiver 160 directly or via the switch 150. There, a corresponding full screen is then displayed. At this moment, the presentation of the second program begins with either a still image or immediately with a motion image. The different beginning of the representation of the second program will be explained in more detail in connection with FIG. In the described embodiment, it should be noted that each of the four encoded video data streams contains all the information to do so

Program 2 on the television receiver 160 to represent.

Second embodiment

Again, assume that the user of the set-top box 120 wants to make a program change from program 1 to program 2. In the present embodiment, the encoder 31 encodes the video signal reproducing the program 2 into two different video data streams shown as streams 1 and 2 in FIG. The video stream "Stream 1" contains all the video data required to represent the program 2, which in the present example are I-frames and P-frames. The second video stream "Stream 2" contains only Frames r _t . However, the frame rate of the second video data stream is greater than that of the first video data stream. This means that the time interval between successive frames in the second video data stream is shorter than the time interval between successive frames I _t in the first video data stream. Both video data streams are in turn transmitted from the encoder via the feed server 51 and the IP distribution network 60 to the multicast replication point 90. After entering a toggle command on the set-top box 120, the microprocessor 155 causes the transmission of the program 1 to be interrupted and, for example, only the two video streams of the program 2 to be transmitted via the VDSL line to the set-top box 120 , The video data of the first

For example, video data stream is stored in the buffer 132 while the video data of the second video stream, which contains only frames, is stored in the buffer

131 are stored. The microprocessor 155 in turn knows the timing of the frames transmitted in the two video streams. In addition, the microprocessor 155 knows the contents of the two video data streams insofar as it knows when a difference image of the first video data stream can be replaced by a frame of the second video data stream containing only frames. In the present example, in response to the switching command and the position information, the microprocessor 155 recognizes that the video stream "stream 2" contains the next displayable frame I _t . Thereafter, the microprocessor 155 transfers the memory

132 and 131 stored video data to the mixer 170, the video data containing the first frame of the second video data stream, in the corresponding position of the first video stream "Stream 1". The output of the mixer 170 is supplied to the decoder 141, for example, which supplies the mixed output signal to the television receiver 160 via the switch 150, for example. Thanks to the use of both

Video data streams, which transmit frames at different times, it is possible to minimize the switching gap occurring when changing the program 1 to the program 2.

3rd embodiment

Again, it is assumed that the user wants to make a program change from program 1 to program 2. In this case, the coding device 31 generates two video data streams for the program 2 provided by the broadcasting station 21. The two video data streams are shown in FIG. 7 as stream 1 and stream 2. As shown in Fig. 7, each video data stream is suitable for displaying the program 2 on the television receiver 160, since each video data stream contains all the picture information (P and I frames). The two video streams differ in that the first video stream "Stream 1" is a wideband video stream enabling high quality reproduction of the program 2, while the second video stream "Stream 2" is a narrow stream video stream representing a replay of the program 2 in poorer quality allows. Another difference is that the frame rate in the narrowband video data stream is higher than in the broadband

Video stream. This means that the time interval between the frames inserted in the narrow-band video data stream is shorter than the time interval between the frames inserted into the broadband video data stream. The time interval between the im For example, full-frame broadband video stream is four seconds, while the time interval between frames inserted in the narrow-band video stream may be 250 milliseconds. Again, the set-top box 120 is aware of where the frames are in the respective video streams.

In the present case, it is assumed that the broadband video data stream is buffered in the buffer 42 while the narrowband video data stream is being stored in the buffer 43. The buffer size of the buffer 42 is larger than that of the buffer 43. The buffer size of the buffer 42 is, for example, dimensioned so that about 50 Mbit of the wideband video data stream can be stored while in the buffer 43 3 Mbit of the narrowband video data stream can be stored. As a result, less data of the narrow-band video data stream is written into the buffer 43 than data of the wideband video data stream is written in the buffer 42 to represent the same program section. As a result, the buffer 43 can also be read out faster than the buffer 42. To ensure that both video streams arrive at the set-top box 120 in a substantially synchronous manner, the narrowband video data stream must be delayed from the broadband video stream during transmission. For this purpose, an unrepresented delay element with a predetermined delay time can be inserted into the transmission path of the narrowband video data stream.

It should be noted at this point that the frames I _t and I _c generated in the video data streams and the Full screen also called I-frame or IDR frame. Thus, when switching, for example, on the TV forcibly results in a brief interruption of the image flow. The length of this interruption, also called zapping gap, is determined by the time span between the confirmation of the

Switching operation and display of the first frame of the new program determines.

The present invention has for its object to provide a method and a data transmission system with which the zapping gap can be reduced.

A central idea of the invention is to distribute the video information to be transmitted to a plurality of parallel, preferably multicast streams, which are transmitted via an IP-based distribution network to at least one distribution point. If the receiving device set up at a user, in particular a set-top box, has the necessary knowledge as to when frames are included in the parallel multicast streams and how possibly several received multicast streams can be combined, the time of presentation of the first frame of the new one Optimized program on the terminal, so that the resulting switching gap can be minimized when changing programs.

It should be noted at this point that in the transmission of audiovisual data streams, the multi-channel sound and other additional information can be transmitted in a separate data stream and supplied to the video information in the set-top box. However, these methods are not the subject of the invention. The above technical problem is solved by a method of reducing the switching gap. The switching gap occurs at a terminal at a program change, ie when switching from a digital video data stream of a first program to a digital video data stream, a second program. The video streams are distributed over an IP-based distribution network to multiple terminals. In order to be able to reduce switching gaps, video information of at least the second program is transmitted via several parallel video data streams to at least one distribution point of the distribution network. The parallel video data streams are differently coded by inserting frames into each video data stream at predetermined times such that at least some of the frames in the parallel video data streams are differently distributed relative to each other. By the term "differently distributed relative to each other" is meant that at least some frames of different video streams are inserted into the video streams at different times. Any current program, referred to herein as the first program, is displayed on the at least one terminal associated with the at least one distribution point. A toggle command is input by at least one user at a receiving device associated with the terminal at which the current program is displayed. In response to the switching command we. the video stream of the second program, which next contains a frame for display on the terminal, is automatically selected by the receiving device. The second program is usually the one program to be changed to. The second program is displayed on the terminal of the at least one user as soon as the first, in selected video data stream received full screen can be displayed. This means that at least the data representing the frame is stored in the receiving device.

Advantageous developments are the subject of the dependent claims.

Also, the video information of the first program can be coded differently via several parallel

Video data streams are transmitted to the at least one distribution point of the distribution network, wherein in each video data stream at predetermined times frames are inserted such that at least some of the frames in the parallel video data streams are distributed differently relative to each other.

In order for the receiving device to find the appropriate video stream, information about the respective positions of the frames in the parallel

Video data streams of the at least one second program to the receiving device. This information may be transmitted in the parallel video streams themselves or in a separate information channel. The appropriate video stream of the second program is then selected by the receiving device in response to the switching command and the position information. A suitable video data stream is to be understood as the video data stream which contains the first displayable frame after the switching command.

In order to reduce the switching gap, the parallel video data streams of at least the second program are coded with the same bandwidth according to an embodiment. In response to the switching command, only the video stream of the second program is selected by the user's receiving device at the distribution point, i. H. requested, the next contains a full screen. In this way, the available bandwidth of the subscriber line connecting the distribution point to the receiving device can be efficiently utilized since only the video data stream is transmitted to the receiving device used in the terminal to display the second program.

According to an alternative embodiment, the video information of at least the second program is transmitted via the distribution network via at least two parallel, differently coded video data streams. The first video data stream of the second program transmits all the video information, while the second video data stream only transmits frames. Since only frames are transmitted in the second video data stream, the time interval between the frames transmitted in the second video stream may be shorter than the time interval between the frames transmitted in the first video stream. According to step d), the receiving device requests at least the first video data stream of the second program in response to the switching command.

In order to make efficient use of the available bandwidth of the subscriber line, the at least two video streams of the second program are only requested together and transmitted to the requesting receiver if the second video stream contains a frame that can be displayed earlier than the first frame in the first video stream.

Otherwise, only the first video stream containing all the video information needs to be transferred.

In order to be able to display the second program in the terminal of the user as quickly as possible, the at least two video data streams of the second program in the receiving device if the second video stream contains a frame that can be displayed earlier than the first frame in the first video stream. The mixing of the two video streams causes the frame transmitted in the second video stream to be the correct one

Position is inserted in the first video stream. For this purpose, for example, the difference image (eg a P-frame in the case of the MPEG standard) of the first video data stream, which carries the same sequence number as the first frame contained in the second video data stream, is replaced by the frame.

According to a further embodiment, the video information of at least the second program is in each case via a broadband and a narrowband

Transfer video data stream over the distribution network. The broadband video data stream can be reproduced as a high-resolution image on the terminal, while the narrow-band video data stream, the second program in poorer quality, but also in a moving form can be displayed. The time interval between the frames transmitted in the narrow-band video data stream is shorter than the time interval between the frames transmitted in the wideband video data stream. According to step d), the video stream of the second program, which next contains a frame for display on the user's terminal, is automatically selected by the receiving device. Since the frame rate in the narrow-band video data stream is higher than that in the wideband video data stream, the switching gap can be significantly reduced compared to the switching gap that occurs when transmitting broadband video data streams alone.

Since both the narrowband and the broadband video stream all the video information of the second

Program included and thus can be displayed on the terminal, for example, both video streams over the Subscriber line are transmitted to the receiving device. If the narrowband video data stream is first selected to represent the second program on the terminal, it will later switch to the wideband video data stream as soon as the wideband and narrowband video data stream receive the same frame for display on the terminal. However, switching to the broadband video data stream only makes sense if the terminal is HDTV-capable.

It should be noted at this point that only the narrowband video data stream is transmitted from the distribution point to the receiving device when the subscriber line supports only narrowband services.

Since the transmission of the narrowband and broadband video data streams via the distribution network for technical reasons leads to a time delay on the receiving device, both video data streams are transmitted to each delayed such that can be switched without interference from the narrowband video data stream to the broadband video data stream at the receiving device.

Advantageously, the transmission of the at least one video data stream of the first program to

Receiving device terminated or interrupted after entering the switching command.

In order to be able to display the second program on the terminal as quickly as possible after the switchover command, after the

Enter the Umschaltbefehls the first frame of the second program shown as a still image on the terminal. In this case, you do not have to wait until in the receiving device In addition to the full screen already more video data are stored, which are required to display a motion picture.

To the available bandwidth of

Subscriber line, such as an ADSL or VDSL line, to be able to use efficiently, the narrowband video data stream of the at least one second program can be transmitted to the receiving device before entering the Umschaltbefehl. The transmission of the broadband video data stream of the second program can be done at a later time. If at a later time the broadband video data stream is received at the receiving device and the receiving device from the narrowband video data stream to the broadband

Switched video data stream of the second program, the transmission of the narrowband video data stream from the distribution point to the receiving device can be stopped. This measure leads to a more efficient utilization of the bandwidth of the subscriber line.

In order to further reduce the switching gap when switching from the first to the second program channel, the switching behavior of the user is preferably monitored on the receiving device. In response to the switching behavior, at least the narrowband video data stream of the at least one second program may be transmitted to the receiving device prior to the input of the switching command. In this way it can be ensured that the first frame of the second program is already stored in the receiving device before or immediately after the input of the switching command and thus can be displayed immediately on the terminal.

Another approach to shorten the switching gap is to see that while entering the

Switching command, for example when entering a multi-digit command, at least the narrowband Video data stream of the at least one second program is transmitted to the receiving device.

In order to make optimum use of the bandwidth on the subscriber line between the distribution point and the receiving device, for example, the currently available bandwidth of the subscriber line to which the receiving device is connected, determined at predetermined times or continuously. Depending on the determined bandwidth, the transmission of the broadband video data stream and / or the narrowband video data stream of one or more programs to the receiving device is performed or interrupted.

The transmitted video data streams may preferably include recorded video programs or live video programs.

The receiving device can be arranged in the user's terminal or can be a set-top box.

The video data streams are expediently transmitted as multicast streams, that is to say the video data streams are intended for a selected group of subscribers.

The above technical problem is also solved by a data transmission system for reducing the switching gap. The data transmission system comprises a first coding means for coding video information of the first program into a plurality of parallel video data streams, wherein frames are inserted into each video data stream at predetermined times such that at least some of the frames are distributed differently in parallel video data streams relative to each other. Conveniently, The first encoder includes a plurality of encoders each generating one of the parallel video streams.

Furthermore, a second coding device is provided for coding video information of the second program into a plurality of parallel video data streams. Again, frames are inserted into each video data stream at predetermined times such that at least some of the frames in the parallel video streams are differently distributed relative to each other.

An IP-based distribution network is provided, via which the parallel video data streams of the first and / or second program are transmitted to at least one distribution point of the distribution network. At the distribution point, at least one receiving device, which is designed to receive at least one video data stream of at least one program, is connected. The at least one receiving device is assigned a terminal for displaying a program. The receiving device is arranged to automatically select, in response to a switching command, the video stream of the second program, which next includes a frame for presentation on the user's terminal, and to decode the selected video stream such that the first received frame of the second program can be displayed on the terminal.

In order to provide the receiving device with information required for selecting suitable video data streams, the first and second coding means for inserting additional information are respectively formed in a separate information channel or in the parallel video data streams of the first and second programs. The information contains information about the respective position of the frames in the parallel video data streams of the first and second programs, respectively. The at least one receiving device selects, in response to the switching command and the additional information, the video data stream which next contains a displayable frame.

In one embodiment, the first and second encoders encode the video information of the first and second programs, respectively, in parallel

Video data streams of the same bandwidth. In this case, in response to the switching command, the receiving apparatus selects only the transmission of the video data stream of the second program at the distribution point, which includes a frame next.

In another embodiment, the first and second encoders encode the video information of the first and second programs, respectively, into at least two parallel video data streams. The first one

Video data stream of the first and second programs contains all the video information, that is, the information required to display motion pictures in the terminal. The second video stream contains only frames. The time interval between the frames transmitted in the respective second video data stream is shorter than the time interval between the frames transmitted in the respective first video data stream. The receiving device then selects, in response to the switching command, transmission of at least one of the two video streams of the second program at the distribution point.

The receiving device is designed to mix the at least two video data streams of the second program, provided that the second video stream contains a frame that can be displayed earlier than the first frame in the first video stream.

In another embodiment, the first and second encoders encode the video information of the first and second programs respectively into a wideband and a narrowband video data stream. The time interval between the encoded in the respective narrow-band video data stream frames is shorter than the time interval between encoded in the respective broadband video data stream frames. The receiving apparatus is in this case configured to automatically select the video stream of the second program, which next contains a frame for display on the user's terminal.

The receiving device can also be designed for switching from the narrowband video data stream to the broadband video data stream of the second program, wherein the switching takes place when the same frame for presentation on the terminal is present in the receiving device for the broadband and the narrowband video data stream.

In order to compensate for a technical delay in the transmission of the narrowband video data stream and the broadband video data stream, a delay element is inserted in the transmission path of the narrowband video data stream. The

Delay time is to be selected such that the broadband and narrowband video data stream can be received synchronously in the receiving device, so that the receiving device can switch from the narrowband video data stream to the broadband video data stream without interference. Advantageously, the receiving device may request at least the transmission of the narrowband video data stream of the second program and / or at least one other program prior to the input of the switching command at the distribution point.

In a preferred embodiment, the receiving device monitors the switching behavior of the user, evaluates the switching behavior and, responsive to the switching behavior, requests at least the transmission of the narrowband video data stream of the second program and / or at least one other program prior to the input of the switching command from the distribution point.

Advantageously, during the input of the toggle command, the receiving device may request at least the transmission of the narrowband video data stream of the second program and / or at least one other program at the distribution point.

In order to make efficient use of the bandwidth provided by the subscriber line, at least one device for determining the current bandwidth is connected at least to the subscriber line to which the receiving device is connected. The receiving device then requests the transmission or interruption of the broadband video data stream and / or the narrowband video data stream of one or more programs as a function of the determined bandwidth

Distribution point on.

The above technical problem is also solved by a receiving device for use in a data transmission system. The receiving device is preferably a set-top box that can be used in a data transmission system. The receiving device has a plurality of input buffers for receiving a plurality of video data streams of at least one program transmitted in parallel. Multiple decoders are used to decode the received video data streams. A controller automatically selects, in response to a switching command, the video stream of the program which next contains a frame for display on a terminal associated with the receiving device. The selected video data stream is decoded by the respective decoder so that the first received frame of the second program can be displayed on the terminal.

The receiving device may include means for mixing at least two video streams. The mixer is primarily for selectively inserting a frame of one video stream into the other video stream so that the new program can be displayed at the terminal faster than would be the case for transmission of a single normal video stream.

The invention will be explained in more detail with reference to several embodiments in conjunction with the accompanying drawings. Show it:

Fig. 1 is a schematic block diagram of a

Data transmission system in which the invention is realized,

Fig. 2 is a schematic representation of the

Resume operation from a narrowband to a wideband video stream,

Fig. 3 shows a switching under Consideration of the switching behavior of the

Fig. 4 shows a switching operation upon inputting a multi-digit switching command, Fig. 5 shows four parallel video data streams having the same bandwidth, Fig. 6 shows two parallel video data streams of the second

Program in which only frames are transmitted in a video data stream, and FIG. 7 shows a broadband video data stream and a narrowband video data stream of the program 2.

An exemplary data transmission system 10, with which switching gaps which occur during program change at a terminal, is shown in FIG. The

Data transmission system 10 comprises an IP distribution network 60, via which, for example, television programs can be distributed to different end users. The television programs are supplied by broadcasters, which are shown in FIG. 1 as broadcasters 20, 21 and 22. For example, the broadcaster 20 delivers the program 1, the broadcaster 21 the program 2 and the broadcaster 22 the program n. The video information contained in the programs 1, 2 and n is supplied to a coding device 30, 31 and 32, respectively. Each coding device is designed such that it can divide the video signals supplied by the broadcaster into a plurality of parallel video data streams which are coded differently. The encoders may, but need not, generate the same number of parallel video streams. In the case that the received video signals are respectively divided into k-parallel video data streams, each encoder 30, 31 and 32 has k encoders which are the simple representation because not shown. More specifically, the video signal coming from broadcaster 20 is supplied to encoder 30, the video signal from encoder 31 provided by broadcaster 21 and the video signal from encoder 32 provided by broadcaster 22. Each encoder generates a plurality of parallel differently coded video streams with the aim of to significantly reduce the switching gap when changing programs. The operation of the encoders 30, 31 and 32 will be explained in more detail below. The video data streams coded by the coding device 30 are buffered in each case in a buffer. For the sake of simplicity, only the two buffers 40 and 41 are shown. Similarly, those of the

Encoder 31 generated video data streams each stored in a buffer, wherein only the two buffers 42 and 42 are shown. The video data streams coded by the coding device 32 are likewise buffered in each case in a buffer, whereby only the two buffers 44 and 45 are shown symbolically. The video data streams of the program 1 stored in the buffers 40 and 41 are supplied to the IP distribution network 60 via a feed-in server 50. The video data streams of the program 2 stored in the buffers 42 and 43 are fed into the IP distribution network 60 via a feed-in server 51. The video data streams of the program n stored in the buffers 44 and 45 are fed into the IP distribution network 60 via a feed server 52. The video streams are then called

Multicast streams supplied to predetermined multicast replication points (MRP). In the present example, it is assumed that the video signals supplied by broadcasters 20, 21 and 22 are transmitted as encoded video data streams to the multicast replication points 70 and 90. As shown in FIG. 1, the Video streams associated with programs 1, 2, and 3 are transferred to multicast replication point 90. The programs 1, 2 and 3 are provided for example by the broadcasters 20, 21 and a third, not shown broadcaster. The multicast replication point 90 may, upon request, distribute the received programs to a plurality of terminals. In the present example, only the two terminals 110 and 160, which may be conventional television receivers, are connected to the multicast replication point 90. For receiving digital video data streams, the television receiver 110 is associated with a video data stream receiving device 100, which is also referred to as a set-top box. The set-top box 100 is connected in the present example via an ADSL line to the multicast replication point 90. The ADSL line, also called Asymmetry Digital Subscriber Line, for example, has a bandwidth of 6 Mbit / s. The television receiver 160 is also connected to the multicast replication point 90 via a set-top box 120. In the present example, the set-top box 120 is connected to the multicast replication point 90 via a VDSL line. For example, the VDSL line has a bandwidth of 50 Mbps. It should be noted that in the television receiver 80, the functionality of the set-top box 120 is implemented. A separate attachment can be dispensed with in this case. For example, the set-top box 120 includes three receive buffers 130, 131, and 132 for receiving three parallel video data streams of a new program to be switched to. It should be noted that the set-top box 120 shown in FIG. 1 does not reflect the complete structure. Of course, the set-top box may have additional buffers for storing the video data streams of other programs, for example, a picture-in-picture representation in the

To enable television receiver 160. Further, a buffer and a decoder for receiving and decoding a P-frames have different sizes. However, the encoder 31 ensures that the two buffers 42 and 43 do not overflow or idle. In addition, it is ensured that the video data from the buffer 42 and 43 are transmitted at a constant bit rate as a video data stream, so that despite fluctuations in the frame sizes always the same amount of data is transmitted. If the wideband video data stream in buffer 132 and the narrowband video data stream are to be stored in the set top box buffer 131, the buffer 131 has a memory size of, for example, 3 megabits, while the buffer 132, for example, has a memory capacity of 50 megabits. For this reason, the narrow-band video data stream can be transmitted to the television receiver 160 faster than the wideband video data stream since video data can be read from the buffer 131 faster than from the buffer 132.

Once the user has entered a toggle command at the set-top box 120, the microprocessor requests

155 the multicast replication point 90, for example, to transmit both the narrowband and the broadband video data stream of the program 2 via the VDSL line to the set-top box 120. At the same time, the transmission of program 1 to the set-top box is interrupted. As already mentioned, the data of the wideband video data stream is stored in the buffer 132 while data of the narrow-band video data stream is stored in the buffer 131. Since the microprocessor 155 knows the temporal position of the frames in the narrowband and wideband video data stream as well as the exact switching timing, it can select the video data stream which will next contain a frame. In the Usually, this will be the narrowband video stream, as it will transmit more frames than the broadband video stream. In the present example, the microprocessor 155 recognizes that the narrowband video data stream next transmits a frame. When at least the video representing the frame is stored in the buffer 131, the microprocessor 155 causes data to be transferred to the decoder 141. The decoded data is then displayed over the switch 150 on the television receiver 160. The duration of the switching gap can thus be significantly reduced since the transmission of the second program can not be carried out first with the first frame in the broadband video data stream, which will be transmitted later, but earlier with the transmission of the first frame of the narrowband video data stream. The microprocessor 155 is programmed to display the high-definition image on the television receiver 160 as soon as the buffer 132 and the buffer 131 each store a frame representing the same program section. At this moment, the video data of the buffer 132 is decoded in the decoder 142 and transferred to the television receiver 160 via the switch 150 instead of the narrow-band video data stream.

The microprocessor 155 may be programmed to interrupt transmission of the narrowband video data stream from the multicast replication point 90 to the set-top box 120 once the decoded wideband video data stream is presented to the television receiver 160.

In Fig. 2, the UmsehaltVorgang program 1 to program 2 and in particular the UmsehaltVorgang from the narrow-band video data stream on the broadband video data stream is shown graphically. The broadband Video data stream is labeled 180, while the narrowband video data stream is labeled 181. As shown in Fig. 2, the program 1 is first displayed on the television receiver 160. At time Tl, a switch command is issued to the set-top box

120 recognized, whereupon the representation of the program 1 on the television receiver 160 is terminated. At time Tl, the microprocessor 155 requests the multicast replication point 90 to transmit both the broadband and narrowband video data streams of the program 2. In the illustrated example, the video data of the P2 frame now partially enters the buffer 132, while the first data of the Il frame of the narrow-band video data stream 181 enters the buffer 131. At the time T2, a frame, namely the I-frame 12, is completely stored in the buffer 131 for the first time. This frame could already be displayed as a still picture of the program 2 on the television receiver 160. However, in order to start the program 2 with moving images, further data must enter the buffer 131, which at least partially represents the next difference image P3. This is the case at time T3, since the following difference image P3 is present at least partially in the memory 131 at this time. Now, the data of the buffer 131 can be given to the decoder 141, so that the decoded narrow-band

Video data stream via the switch 150 as a motion picture on the television receiver 160 can be played. In other words, the moving picture representation of the program 2 starts at time T3. A still image reproduction of the program 2 could, as I said, already take place at time T2. As can be seen from FIG. 2, at the time T4, a full frame 16 of the wideband video data stream is completely stored in the buffer 132 for the first time. However, in this case it is not yet possible to switch over to the broadband video data stream since the same frame 16 of the narrowband video data stream is not yet present in the memory 131. Only at the time T5 is also in the memory 131th the frame 16 of the narrowband video data stream. At the time T6 are in the buffer memory 132 all video data of the frame 16 and additional data at least the subsequent difference image P7. Also in the buffer 131 are all the data of the frame 16 and at least partially data of the difference image P7 of the narrowband video data stream. Now, a switch from the narrow-band video data stream to the broadband video data stream can be made without interference. For this purpose, the data stored in the buffer 132 is given to the decoder 142. The decoded video data of the broadband video data stream are transferred to the television receiver in the decoder 142 via the switch 150 and reproduced there.

In order to be able to further shorten the switching gap when switching from one program to another program, the set-top box 120 is designed such that it transmits an expected program from the set-top prior to the actual input or activation of a switching command Box 120 requests from the multicast replication point 90.

The microprocessor 155 of the set-top box 120 may be implemented to handle the switching behavior of the

User monitors and learns. For example, assume that the microprocessor 155 has recognized that the user is switching back and forth between the first and second programs at regular intervals. Furthermore, it is assumed that the user has recently selected program A and

Program A is displayed on the television receiver 160. The following switching behavior is shown graphically in FIG. In Fig. 3, lower case letters indicate a narrow-band video data stream or low-quality picture reproduction. Capital letters indicate a broadband video data stream or high-resolution image reproduction. FIG. 3 shows two graphs, one showing the image content on the television receiver 160 and a graph representing the bandwidth on the VDSL line between the multicast replication point 90 and the set-top box 120. First, only the broadband video data stream of the program A is transmitted to the set-top box 120 and the associated program A is displayed on the television receiver 160. The program A is broadcast, for example, by the broadcaster 20, while the program B is provided by the broadcaster 21. It is further assumed that the encoder 31 transmits the program B over a narrowband and a wideband video data stream, as previously described. Due to the learned switching behavior of the user or by entering the letter "B" on the set top box 120, the microprocessor 155 at one time requests the multicast replication point 90, in addition to the broadband video data stream of the program A, the narrowband one

Video stream "b" of the program B to transmit. The simultaneous transmission of the narrow-band video data stream "b" of the program B and the wideband video data stream "A" of the program A is reproduced in the lower illustration of FIG. At a later time, the confirmation of the actual switching command, which is marked OK in FIG. 3, follows. Thereafter, the microprocessor 155 requests the multicast replication point 90, in addition to the narrowband video data stream "b" and the broadband video data stream

To transmit "B" of the program B and to stop the transmission of the program A. This situation is shown in Fig. 3 with an empty image content. Since the microprocessor 155 has already requested the transmission of the narrowband video data stream "b" of the program B before the actual switching operation, it can be assumed that a frame of the narrowband is very fast Video data stream is stored in the buffer 131, so that the program B, albeit in poorer quality, can be displayed on the television receiver 160 without much time delay. The switching from narrow-band video data stream "b" to the broadband video data stream "B" of the second program B takes place in the manner described above and is illustrated once more in FIG.

According to an embodiment variant, the transmission of the narrowband video data stream "b" to the set-top box 120 is terminated as soon as the broadband video data stream "B" is transmitted in decoded form via the switching device 150 to the television receiver 160.

An alternative method of reducing the switching gap is shown in FIG.

It is now assumed that the user would like to select the program D at the set-top box 120 by means of a three-digit switching command. Furthermore, it is assumed that in this case all necessary programs A, B, C and D are transmitted by a corresponding coding device in each case via a narrowband and broadband video data stream to the multicast replication point 90.

Fig. 4 shows the UmsehaltVorgang and the transmission of the respective video data streams via the VDSL line to the set-top box 120. First, it is assumed that only the broadband video data stream of the program A is transmitted to the set-top box 120 (see bandwidth diagram) and the associated program A is displayed on the television receiver 160 (see image content diagram). Now, the user enters the first digit of the three-digit switching command, for example a 1 at the set-top box 120, which corresponds to the program B. Of the

Microprocessor 155 interprets the entry of the first digit as a possible switching instruction to program B and then requests the transmission of the video B streamed video data stream "b" from the multicast replication point 90. As before, however, the program A is transmitted to the television receiver 160. Now the user gives the second digit of the three digit toggle command, e.g. As the number 2, a. The microprocessor 155 interprets the two-digit input value "12" as a possible switching instruction to the program C. Thereafter, the microprocessor 155 requests the multicast replication point 90 to transmit the narrowband video data stream of the program C and interrupt the transmission of the narrowband video data stream of the program B. As before, the program A is transmitted to the television receiver 160. Now the user gives the last digit of the three digit toggle command, e.g. As the number 3, a. The microprocessor 155 interprets the three-digit input value "123" as a switching command to the program D. Thereafter, the microprocessor 155 requests the multicast replication point 90 to transmit the narrowband video data stream of the program d and interrupt the transmission of the program C narrow-band video data stream. Still, however, the program A is displayed on the television receiver 160 (see image content diagram). Finally, the user confirms his program selection by entering the command "OK." Thereafter, the set-top box 120 requests the transmission of the broadband video data stream of the program D and stops the transmission of the program A on the television receiver 160 Program D has already been stored in the set-top box 120 during the playback of the program A, there will be a high probability at the time of confirmation of the switching command or a short time thereafter a frame of the narrow-band video data stream in the set-top box 120, to be displayed on the television receiver 160. Switching from the narrowband video data stream to the wideband video data stream is done in the manner described with respect to the third embodiment.

An advantageous measure provides that after the confirmation of the switching command, the set-top box 120 in turn requests the transmission of the narrow-band video data stream of the program A (see bandwidth diagram in FIG. 4). In this case, the microprocessor 155 knows the switching behavior of the user and expects the user to switch back to program A at a later time.

The person skilled in the art recognizes that the two exemplary embodiments illustrated represent only two options for minimizing a switching gap when switching from one program to another program by taking into account the switching behavior of a user. Other switching procedures may take into account the time of day.

For example, the set-top box 120 may be programmed to simultaneously request, in addition to the broadband video stream of program A, the narrowband video stream of a program B to which the user is expected to switch, for example, between o.o o and oo o'clock. It can be seen that within the scope of the invention there are any various switching operations that the set-top box 120 can automatically take into account. The only important thing is that in addition to the currently displayed program is already a narrowband

Video stream of a future program to be transmitted from the multicast replication point 90 to the set-top box.

To the available bandwidth of

Subscriber line, in the present example, for example, the VDSL line between the multicast Replication point 90 and the set-top box 120 to be able to use efficiently, the traffic load is determined via this line. For this purpose, a set up at the subscriber device, such as a network access device, calculate the traffic load. In

Depending on the traffic load, the transmission of narrowband and / or broadband video data streams of one or more programs can then be requested or terminated.

In one possible scenario, for example, two television receivers are connected to the VDSL line via two parallel-connected set-top boxes. If a current available bandwidth is determined, which allows the transmission of a broadband and narrowband video data stream over the VDSL line, so can be displayed on a television receiver, a high-resolution image, while the other television receiver only a picture with poorer quality can be displayed. Depending on the determined available bandwidth of the

VDSL line can be requested during operation new video streams from the multicast replication point 90 or the transmission of video streams are selectively interrupted. Thus, the quality of a program currently displayed on the television receiver 160 may be temporarily displayed at low quality when higher priority services need to be transmitted over the VDSL line.

To make a smooth transition when switching from one

To achieve program to another program or from a narrowband video data stream to a wideband video data stream and vice versa, well-known fading techniques can be used. It is also conceivable that the image area used on the television receiver 160 is reduced if narrow-band video data streams are to be displayed. Also the Use of gray shades when switching images by selectively superimposing two images can be used.

Furthermore, it is conceivable that the transmission of a program via parallel video data streams can also be activated or deactivated by the content of the programs to be transmitted or in dependence on the broadcaster. The encoders 30, 31 and 32 are then respectively driven by a central controller to either generate a plurality of parallel, differently encoded video streams or just a video stream carrying the video signals of the program.

Although it has been explained in the foregoing embodiments that the set-top box 120 requests transmission of video streams or interruption of transmission of video streams at the multicast replication point 90, this does not necessarily mean that all of them are for the set-top box 120 provided video data streams at the multicast replication point 90. Since the IP distribution network 60 may have a hierarchical structure of multicast replication points, the requested video data streams may also be cached in higher-level multicast replication points. In this case, the multicast replication point 90 sends corresponding request commands to the parent multicast replication points. Reference character list for FIG. 1

10 data transmission system

20 broadcaster

21 broadcaster

22 broadcasting company

30 coding device

31 coding device

32 coding device

40 buffers

41 buffers

42 buffers

43 buffers

44 buffers

45 buffers

50 feed-in server

51 feed-in server

52 Infeed Server 60 IP Distribution Network

70 multicast replication point

80 television receivers

90 multicast replication point

100 set-top box

110 television receivers

120 set-top box

130 receive buffer

131 receive buffer

132 receive buffer

140 decoders

141 decoders

142 decoders

150 switching device

155 microprocessor

160 television receivers

170 mixers

Claims

claims

A method for reducing the switching gap that occurs at a terminal (160) when switching from a digital video stream of a first program to a digital video stream of a second program, the video streams over an IP based distribution network (60)

Terminal devices (80, 110, 160) are distributed, wherein according to the method a) video information of at least one second program over several parallel video data streams to the at least one distribution point (70, 90) of the

Distributed network (60), wherein in each video data stream at predetermined times frames are inserted such that at least some of the frames in the parallel video data streams are distributed differently relative to each other, b) the first program on the terminal (160) of at least one user, which is associated with the at least one distribution point (90) is currently displayed, c) a switching command by the at least one user at a receiving device (120) is input; d) in response to the switching command, the video data stream of the second program, which is next a frame for display at the terminal

(160) of the user, is automatically selected by the receiving device (120), and e) the second program on the terminal (160) of the at least one user is displayed as soon as the first, received in the selected video data stream full screen is displayed.

2. The method of claim 1, wherein

Video information of the first program is transmitted over multiple parallel video data streams to the at least one distribution point (90) of the distribution network (60), wherein each video data stream is inserted at predetermined times frames such that at least some of the frames in the parallel video data streams are differently distributed relative to each other ,

3. The method according to claim 1 or 2, characterized in that

Information about the respective position of the frames in the parallel video streams of the at least one second program are transmitted to the receiving device (120) of the at least one user, and the appropriate video stream of the second program is selected by the receiving device (120) in response to the switching command and the position information becomes.

A method according to claim 1, 2 or 3, characterized in that the parallel video streams of at least the second program have the same bandwidth, and in response to the switching command, only the video stream of the second program from the user's receiving device (120) at the point of distribution ( 90) is selected, which next contains a full screen.

5. The method of claim 1, 2 or 3, characterized in that the video information of at least the second program respectively via. at least two parallel, differently coded video streams are transmitted over the IP distribution network (60), the first video stream of the second program transmitting all the video information while the second video stream is only frames, the temporal distance between the frames transmitted in the second video stream being shorter is as the time interval between the first

Video frames, and according to step d), the receiving device selects at least the first video stream of the second program in response to the switching command.

6. The method according to claim 5, characterized in that the receiving device in response to the switching command selects the at least two video streams of the second program and that the at least two video streams of the second program are transmitted in parallel to the receiving device (120) when the second video data stream is a frame which may be displayed earlier than the first frame in the first video stream.

7. The method according to claim 5 or 6, characterized in that the at least two video streams of the second program are mixed in the receiving device (120) as long as the second video stream contains a frame that can be displayed earlier than the first frame in the first video stream.

8. The method of claim 1, 2 or 3, characterized in that the video information of at least the second program in each case via a broadband and a narrowband video data stream over the IP distribution network (60) are transmitted, wherein the time interval between the transmitted in the narrow-band video data stream Frames is shorter than the time interval between the frames transmitted in the broadband video stream, and that according to step d) the video stream of the second program which next contains a frame for presentation on the user's terminal (160) is automatically received by the receiving device (120). is selected.

9. The method according to claim 8, characterized in that when first the narrow-band video data stream is selected and displayed on the terminal (160) is switched to the broadband video data stream, as soon as in the receiving device for the broadband and the narrowband video data stream the same frame for display on Terminal (160) is present.

10. The method according to claim 8 or 9, characterized in that the broadband and narrowband video data stream of the first program and the wideband and narrowband video data stream of the second program are delayed to each other via the IP distribution network (60) to be transmitted.

11. The method according to any one of claims 2 to 10, characterized in that the transmission of the at least one video data stream of the first program to the receiving device (120) after

Input of the switching command is terminated or interrupted.

12. The method according to any one of the preceding claims, characterized in that

, after entering the Umschaltbefehls the first frame of the second program is displayed as a still image on the terminal (160).

13. The method according to any one of claims 8 to 10, characterized in that at least the narrow-band video data stream of the at least one second program before the input of the switching command to the receiving device (120) is transmitted.

14. The method according to claim 13, characterized in that the switching behavior of the user is monitored and that, in response to the switching behavior, at least the narrowband video data stream of the at least one second program before the input of the switching command to the receiving device (120) transmitted becomes .

15. The method according to any one of claims 8 to 10, characterized in that during the input of the Umschaltbefehls, in particular a multi-digit Umschaltbefehls, at least the narrow-band video data stream of the at least one second program to the receiving device (120) is transmitted.

16. The method according to any one of claims 8 to 15, characterized in that the current bandwidth of the subscriber line to which the receiving device (120) is connected, is determined at predetermined times or continuously, and that depending on the determined bandwidth, the transmission of the broadband Videdatenstroms and / or the narrow-band video data stream of one or more programs to the receiving device (120) takes place or is interrupted.

17. Method according to one of the preceding claims, characterized in that the video data streams contain recorded video programs or live video programs.

18. The method according to any one of the preceding claims, characterized in that the receiving device (120) arranged in the terminal (160) of the user or a set-top box.

19. The method according to any one of the preceding claims, characterized in that the video data streams are transmitted as multicast streams.

A data transmission system (10) for reducing the switching gap that occurs at a terminal (160) when switching from a digital video stream of a first program to a digital video stream of a second program, comprising:

- A first encoder (30) for encoding video information of the first program into a plurality of parallel video data streams, wherein in each video data stream at predetermined times

Frames are inserted so that at least some of the frames in the parallel video streams are differently distributed relative to each other; second encoder means (31) for encoding video information of the second program into a plurality of parallel video streams, with frames being inserted into each video stream at predetermined times that at least some of the frames in the parallel

Video data streams are distributed differently relative to each other

- An IP-based distribution network (60) for transmitting the parallel video data streams of the first and second programs to at least one distribution point (70, 90) of the distribution network (60) to which at least one receiving device (120), which for receiving at least one video data stream at least a program is formed, is connected, wherein the at least one receiving device (120) is a terminal

(160) is associated with presenting a program, and wherein the receiving device (120) is arranged to respond to the video data stream of the second program in response to a switching command, which is next a frame for display on the terminal

(160) of the user, automatically selects and decodes the selected video data stream so that the first received frame of the second program is displayable on the terminal (160).

21. Data transmission system according to claim 20, characterized in that the first and second coding means (30, 31) for inserting additional information are each formed in a separate information channel or in the parallel video data streams of the first or second program, wherein the information is information about the comprise respective positions of the frames in the parallel video data streams of the first and second programs, respectively, and the at least one receiving device (120) selects the video data stream which will next contain a displayable frame in response to the switching command and additional information.

22. Data transmission system according to claim 20 or 21, characterized in that the first and second coding means (30, 31) convert the video information of the first or second program into parallel video data streams of the same bandwidth and that the receiving device (120), in response to the switching command, requests only the transmission of the video stream of the second program from the distribution point (90) which next contains a frame.

23. The data transmission system according to claim 20 or 21, characterized in that the first and second coding means (30, 31) respectively encode the video information of the first and second programs into at least two parallel video data streams, the first respective video data stream of the first and second programs contains the entire video information, while the second video data stream contains only frames, wherein the time interval between the transmitted in the second video stream frames is shorter than the time interval between the transmitted in the respective first video data frames, and in that the receiving device (120) in response to the

Switching command requests the transmission at least the first video data stream of the second program at the distribution point (90).

A data transmission system according to claim 23, characterized in that the receiving device (120) mixes the at least two video streams of the second program if the second video stream contains a frame which can be displayed earlier than the first one

Full screen in the first video stream.

25. Data transmission system according to claim 20 or 21, characterized in that the first and second coding means (30, 31) respectively encode the video information of the first and second programs into a wideband and a narrowband video data stream, the time interval between the respective narrowband ones Video data stream coded frames is shorter than the time interval between the frames encoded in the respective broadband video stream, and that the receiving device (120) automatically selects the video stream of the second program which next contains a frame for display on the user's terminal (160) , is trained.

26. Data transmission system according to claim 25, characterized in that the receiving device (120) for switching from the narrow-band video data stream to the broadband

Video data stream of the second program is formed, wherein the switching takes place as soon as the same frame for presentation on the terminal (160) is present in the receiving device (120) for the broadband and the narrowband video data stream.

27. A data transmission system according to claim 25 or 26, characterized by a delay element for delaying the transmission of the wideband and narrowband video data stream of the first program and the wideband and narrowband video data stream of the second program relative to each other.

A data transmission system according to any one of claims 25 to 27, characterized in that the receiving device (120) requests at least the transmission of the narrowband video data stream of the second program and / or at least one other program prior to the input of the switching command at the distribution point (90).

29. Data transmission system according to claim 28, characterized in that the receiving device (120) monitors the switching behavior of the user, evaluates and responsive to the switching behavior at least the transmission of the narrowband video data stream of the second program and / or at least one other program before entering the Umschaltbefehls at the distribution point (90).

A data processing system according to any one of claims 25 to 27, characterized in that the receiving device (120) requests at least the transmission of the narrowband video data stream of the second program and / or at least one other program at the distribution point (90) during the input of the switching command.

31. Data transmission system according to one of claims 20 to 30, characterized by at least one means for determining the current bandwidth at least at the subscriber terminal to which the receiving device (120) is connected, wherein the receiving device (120) depending on the determined bandwidth, the transmission or

Requesting interruption of the wideband video data stream and / or the narrowband video data stream of one or more programs at the distribution point (90).

32. Data transmission system according to one of claims 20 to 31, characterized in that the receiving device (120) arranged in the terminal (160) of the user or a set-top box.

33. receiving device (120), in particular a set-top box, for use in a data transmission system according to one of claims 20 to 32, with a plurality of input buffers (130, 131, 132) for receiving a plurality of video data streams of at least one program transmitted in parallel. a plurality of decoders (140, 141, 142) for decoding the received video streams, control means (155) responsive to a switching command for containing the video stream of the program which next contains a frame for display on a terminal (160) associated with the receiving device, automatically selects and feeds the respective decoder (140, 141, 142) so that the first received frame of the second program can be displayed on the terminal (160).

34. Receiving device according to claim 33, characterized by a device (170) for mixing at least two video data streams.