DE102011107161A1 - Methods and devices for low-delay switching on or switching to a digital video signal - Google Patents

Abstract

The invention relates to 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).
The invention further relates to 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):
- receiving (100) an access request (300) with respect to the video signal (11); (10);
- 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.
The invention further relates to a server and a receiving device.

Description

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-coded, with respect to the prior art greatly reduced and barely perceptible to the viewer delay ,

In the prior art, transmission of video signals over multicast channels results in a time delay between the moment the particular viewer dials the video signal and the moment the video signal is then presented to the viewer. In order to enable a transmission of a digital video signal with low data rate, in the prior art for video signal transmissions such. As DVB (terrestrial, satellite) or IP television uses a coding that takes into account differences in temporally successive image frames and thus leads to high compression. Such codes are z. As MPEG encoding (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 so that the decoding can be started can. 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.

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 reordering 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.

• – Empfangen (200) einer Zugriffsanforderung (300) bezüglich des Videosignals (11);
• – Senden (210) mindestens eines intrakodierten Frames (52) eines Streams (51) aus intrakodierten Frames (52) des Videosignals (11).

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, in a server ( 10 ) be performed:

• - Receive ( 200 ) an access request ( 300 ) with respect to the video signal ( 11 );
• - send ( 210 ) at least one intra-coded frame ( 52 ) of a stream ( 51 ) from 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 video signal is preferably a video signal encoded by MPEG standard (MPEG-1, MPEG-2 or MPEG-4) or H.264 standard. Preferably, it is the digital video signal of a TV provider. The source of this signal is preferably in the range of influence of the TV provider and there, in this origin the signal is encoded such that different frames are inter coded, i. H. Dependencies of temporally consecutive frames were considered for compression.

The receiving device is preferably a set-top box in the sphere of influence of the television viewer and / or a TV tuner or Internet receiver integrated in a television set.

The server is preferably an arithmetic unit that is set up and programmed to perform a rapid channel change. Preferably, the server is within the sphere of influence of the TV provider, z. B. will open On the other hand, the same server encodes the video signal on the other hand carries out the transmission method according to the invention. Particularly preferably, the server is a lying between the TV provider and the receiver of the viewer server, on the one hand receives the video signal from the TV provider and further performs the inventive method, so that the viewer on the receiver then a quick channel change or a quick turn on can perform a channel.

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. The server preferably receives the access request from the receiving device. The reception takes place z. B. via a cable TV network, Internet and / or via a radio link.

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 z. For example, 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 z. As an MJPEG stream or an MPEG or H.264 stream, each consisting exclusively of keyframes, which is also possible with this code (MPEG, H.264), although unusual in the prior 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.

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.

• – Senden (220) mindestens eines interkodierten Frames eines Streams (31) mit interkodierten Frames des Videosignals (11); sowie bevorzugt die Schritte:
• – Feststellen (230) ob, eine Zeitdauer T abgelaufen ist oder ob eine Bestätigungsnachricht von dem Empfangsgerät (20) vorliegt; wenn eine Zeitdauer T abgelaufen ist oder wenn eine Bestätigungsnachricht vorliegt:
• – Stoppen (240) des Sendens des Streams (51) aus intrakodierten Frames (52).

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

• - send ( 220 ) at least one inter-coded frame of a stream ( 31 ) with inter-coded frames of the video signal ( 11 ); and preferably the steps:
• - Determine ( 230 ), whether a time period T has elapsed or whether an acknowledgment message from the receiving device ( 20 ) is present; if a time period T has expired or if a confirmation message is present:
• - To stop ( 240 ) of sending 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 of inter-coded frames preferably also contains intra-coded frames at certain intervals (eg so-called I-frames or K-frames or even keyframes).

The time period T is preferably an empirically determined time. Particularly preferably, the time T is fixed and is the double, preferably simple time equivalent of a so-called "group of pictures (GoP)", d. H. a group of frames that 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 when a K-frame was received via the TV provider's multicast stream, the time T is longer than when the access request is received, just before the next K-frame of the TV provider expects becomes.

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. It is preferred with the stream with inter-coded frames or with the stream of intra-coded frames also sent an associated soundtrack.

• – Dekodieren des mindestens einen interkodierten Frames des Streams (31) mit interkodierten Frames des Videosignals (11) zu mindestens einem intrakodierten Frame (52).

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 by the TV provider. The decoding preferably also includes an encoding, z. In an MJPEG format or an MPEG or H.264 format with only K-frames. Preferably, the decoding also includes subsampling and / or compression gain to reduce quality. Preferably, the reduction in quality is preferably carried out depending on the bandwidth currently available in the network. For example, if too little bandwidth is available at the moment, the quality of the intra-coded frames is further reduced.

• – Zwischenspeichern des mindestens einen interkodierten Frames des Streams (31) mit interkodierten Frames des Videosignals (11) in einen Zwischenspeicher;
• – Auslesen einer Überbrückungssequenz (33) mit interkodierten Frames aus dem Zwischenspeicher, wobei die Überbrückungssequenz (33) mit einem intrakodierten Frame beginnt.
• – Senden (221) der Überbrückungssequenz (33) mittels einer Burst-Übertragung über eine Unicast-Verbindung zum Empfangsgerät (20).

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

• - buffering the at least one inter-coded frame of the stream ( 31 ) with inter-coded frames of the video signal ( 11 ) in a cache;
• - reading a bridging sequence ( 33 ) with inter-coded frames from the buffer, the bridging sequence ( 33 ) begins with an intra-coded frame.
• - send ( 221 ) of 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 bridged by the inventive transmission of the stream of intra-coded frames.

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

Preferably, the bypass sequence, analogous to the preferred embodiment of the intra-coded frames, has a reduced quality, e.g. B. due to a reduced resolution or a higher intra-compression of the individual frames, on, with particular preference the quality is selected depending on the currently available bandwidth.

Burst transmission uses a higher bandwidth compared to the normal transmission of the video signal, but only for a short time, and thus shortens the time normally required to transmit a certain number of frames.

• – Senden (250) mindestens eines interkodierten Frames eines Streams (31) mit interkodierten Frames eines anderen, zuvor angeforderten Videosignals (12).

In a further transmission method according to the invention, the following step is performed first:

• - send ( 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 inventive method can be integrated into a switching process by first the video signal of one channel is sent, and then switched to another channel by means of the aforementioned steps.

• – Empfangen (100) einer Zugriffsanforderung (300) bezüglich des Videosignals (11);
• – Senden (110) der Zugriffsanforderung (300) an den Server (10);
• – Empfangen (120) mindestens eines intrakodierten Frames (52) eines Streams (51) aus intrakodierten Frames des Videosignals (11) von dem Server (10);
• – Dekodieren (130) des mindestens einen intrakodierten Frames (52) zu mindestens einem Bildframe (21);
• – Anzeigen (140) des mindestens einen dekodierten Bildframes (21) aus dem Stream (51) aus intrakodierten Frames.

The object is furthermore achieved, in particular, by a receiving method for the delay-free reception of 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 ) be performed:

• - Receive ( 100 ) an access request ( 300 ) with respect to the video signal ( 11 );
• - send ( 110 ) of the access request ( 300 ) to the server ( 10 );
• - Receive ( 120 ) at least one intra-coded frame ( 52 ) of a stream ( 51 ) from intra-coded frames of the video signal ( 11 ) from the server ( 10 );
• - decode ( 130 ) of the at least one intra-coded frame ( 52 ) to at least one image frame ( 21 );
• - Show ( 140 ) of the at least one decoded image frame ( 21 ) from the stream ( 51 ) from intra-coded frames.

In this way, z. B. in a turn-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 possible. The receiving device does not have 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 or a control 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.

• – Empfangen (150) mindestens eines interkodierten Frames eines Streams (31) mit interkodierten Frames des Videosignals (11) von dem Server (10) und bevorzugt Speichern des mindestens einen interkodierten Frames in einen Videopuffer (30);
• – Feststellen (160), ob ausreichend interkodierte Frames für eine Dekodierung vorliegen; wenn ausreichend interkodierte Frames für eine Dekodierung vorliegen, zusätzlich umfassend die Schritte:
• – Dekodieren (170) der vorhandenen interkodierten Frames zu Bildframes (21);
• – Anzeigen (180) der dekodierten Bildframes (21) aus dem Stream (31) mit interkodierten Frames und bevorzugt
• – Senden einer Bestätigungsnachricht an den Server (10).

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

• - Receive ( 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 into a video buffer ( 30 );
• - Determine ( 160 ), whether there are enough inter-coded frames for decoding; if there are enough inter-coded frames for decoding, additionally comprising the steps:
• - decode ( 170 ) of the existing inter-coded frames to image frames ( 21 );
• - Show ( 180 ) of 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 TV provider's multicast stream and the normal process of preparing the display of the bi1d frames from this multicast stream, including pre-buffering and decoding, as soon as there are enough frames 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.

• – Empfangen einer Überbrückungssequenz (33) mit interkodierten Frames mittels einer Burst-Übertragung über eine Unicast Verbindung zum Server (10), wobei die Überbrückungssequenz (33) mit einem intrakodierten Frame beginnt;
• – Speichern (152) der Überbrückungssequenz (33) mit interkodierten Frames in den Videopuffer (30).

A further receiving method according to the invention additionally comprises 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 ), where the bridging sequence ( 33 ) begins with an intra-coded frame;
• - To save ( 152 ) of 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.

• – Anzeigen (190) mindestens eines Bildframes (21) eines anderen, zuvor angeforderten Videosignals (12).

In a further reception method according to the invention, the following step is performed first:

• - Show ( 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 process by first the video signal of a first television channel is displayed and then displayed with the aid of the inventive method steps at the end of the video signal of another television channel was switched to.

The object is further achieved in particular by a receiving device ( 20 ) for the low-delay reception of 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 ), the receiving device ( 20 ) An institution ( 80 ) to send one Access request ( 300 ) with respect to the video signal ( 11 ) to the server ( 10 ) and the video decoder ( 50 ) a second input ( 56 ) for receiving intra-coded frames ( 52 ) of a stream ( 51 ) from intra-coded frames ( 52 ) having.

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. Preferably, however, the receiving device 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 that 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 according to the invention ( 20 ) 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 frames are present in the video buffer for the decoding of the last arrived frame in the video buffer.

In a further embodiment of the receiving device according to the invention ( 20 ) the facility ( 80 ) for sending an access request ( 300 ), a confirmation message to the server ( 10 ) as soon as frames with inter-coded frames in the video buffer ( 30 ) are decodable.

For this purpose, the receiving device preferably has a return channel to the server.

The problem is further solved in particular by a server ( 10 ) for transmitting a digital, originally inter-coded video signal ( 11 ) to a receiving device ( 20 ), whereby the server ( 10 ) at least one institution ( 90 ) for receiving an access request ( 300 ) with respect to the video signal ( 11 ) and at least one device ( 45 ) for transmitting at least one intra-coded frame ( 52 ) of a stream ( 51 ) from 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 can be registered 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. Particularly preferably, the access request also contains the information about which receiving device has sent the access request. In the second case, statistics on the viewing habits of the users of a respective receiving device can be created.

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

In this way, a stream consisting of intra-coded frames can be created from the multicast stream received by the TV provider. In the video buffer while the server incoming original data from the TV provider (with inter-coded frames) can be stored. The video buffer is preferably so large that two GoPs can be stored in the video buffer. Preferably, the server also has a Decoder downstream buffer 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 inter-coded video signal.

In a further embodiment of the server according to the invention ( 10 ) the facility ( 90 ) for receiving an access request ( 300 ) is additionally set up, a confirmation message from the receiving device ( 20 ) and / or determine the expiration of a time period T.

In a further embodiment of the server according to the invention ( 10 ) is the server ( 10 ) in a cable headend ( 60 ) arranged.

In this way, users who are in a tree of a cable TV network about z. B. IP television, by means of such a server quickly aufschaltbar on a particular video signal or switchable between two different video signals, without causing large delay times are visible to the user.

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

The invention will now be further illustrated by way of example with reference to the drawings. Hereby show:

1 an overview of an inventive transmission method,

2 an overview of a receiving method according to the invention,

3a 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,

3b 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,

3c 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,

4 a scheme of a switching operation without measures for reducing the switching delay,

5 a diagram of a switching operation using the transmission and reception method according to the invention

6 a schematic of a switching operation using the transmission and reception method according to the invention, in addition a bridging sequence is sent and received.

1 shows an overview of an inventive transmission method.

In a first step 200 If an access request is received by a receiving device, then in one step 210 a sequence 51 from intra-coded frames 52 of the requested video signal 11 sent 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 transmission of the intra-coded frames 52 a stream 31 from inter-coded frames corresponding to that of the TV provider, forwarded to the receiving device in this example by multicast. In one step 230 It is then checked whether a certain time T has expired or if there is a confirmation message from the receiving device. If this is not the case, the step will continue 210 repeated and there will continue to be intra-coded frames 52 sent to the receiving device. If a time T has expired or a confirmation message is present in one step 240 sending the intra-coded frames 52 stopped.

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 can already make a display due to the inter-coded stream, this is via a confirmation message from the receiving device 20 is signaled or this is estimated over a time T and then the transmission of the intra-coded frames is then reset.

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

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

In this way receives the receiving device 20 after an access request 300 immediately a set of instantaneously decodable frames 52 why the video signal 11 with hardly any delay on the receiver 20 shortly after the occurrence of the access request 300 can be displayed.

In another embodiment of the invention is in one step 150 a stream 31 with inter-coded frames of the video signal 11 from the server 10 receive. This stream 31 is z. B. the forwarded multicast stream of the TV provider. In one step 160 It determines if there are enough inter-coded frames for decoding. If not, the step becomes 150 it repeats and gets at least one more inter-coded frame from the server 10 receive. If the number of inter-coded frames is sufficient, in one step 170 the decoding of the inter-coded frames into image frames 21 made and it will be the image frames 21 that comes from the stream 31 were decoded in one step 180 the user of the receiving device 20 displayed.

This way, after a certain amount of time and as soon as enough frames are available to the video signal 11 represented by inter-coded received frames, the video signal 11 also shown in inter-coded frames. Thus, also on a bandwidth-friendlier representation of the video signal 11 switchable after a certain time and the intra-coded frames 52 do not need anymore from the server 10 be sent.

In one step 190 beforehand another video signal to the user of the receiving device 20 shown. In this case, by carrying out the method according to the invention then switching over with a very short time delay becomes possible.

3a shows a representation of a server according to the invention 10 and receiving devices according to the invention 20 . 20 ' in the state of receiving a previous video signal before a switching operation by the receiving apparatus 20 ' , In this example, the server is located 10 in the headend 60 a cable television network 70 , For each channel, for which a fast switching or fast switching is offered, is a device 45.1 respectively. 45.2 for transmitting at least one intra-coded frame of a stream of intra-coded frames of the respective video signal. In addition, the server rejects 10 An institution 90 for receiving an access request 300 with respect to a video signal. In this example, the server additionally has video buffers 30.1 . 30.2 as well as decoder 40.1 . 40.2 on. Via a coaxial cable network 70 are receivers 20 . 20 ' connected to the server. Each receiver 20 . 20 ' has a facility 80 . 80 ' to send a channel request 300 to the server 10 on. Each receiver 20 . 20 ' also has a video buffer 30 . 30 ' as well as a video decoder 50 . 50 ' with a first entrance 55 . 55 ' and a second entrance 56 . 56 ' on.

In operation of the invention, the receiving device receives 20 ' the multicast stream 31.2 the video signal that was previously requested and stores it in the video buffer 30 ' , It then gets around the size of the video buffer 30 ' delayed and via the first decoder input 55 ' the decoder 50 ' fed and decoded there. The same takes place for another receiver 20 and the inter-coded stream 31.1 another video signal. The stream 31.1 will be in the video buffer 30.1 in the server 10 cached and then a video decoder 40.1 supplied, which decodes the inter-coded frames into intra-coded frames, and to a device 45.1 for transmitting at least one intra-coded frame of a stream of intra-coded frames of the video signal forwarded. The user of the receiving device 20 ' now want to switch to the video signal, which also the receiver 20 over the stream 31.1 receives and transmits over the device 80 ' a channel request 300 to the server 10 by means of the device 90 receives.

3b shows a representation of a server according to the invention 10 and receiving devices according to the invention 20 . 20 ' in the state of receiving a stream of intra-coded frames of the requested video signal during the switching operation. After the server 10 the channel request 300 by means of the device 90 has received, this sends by means of the device 45.1 a stream 51 from intra-coded frames to the receiving device 20 ' , In the receiver 20 ' becomes the stream 51 over the second decoder input 56 ' the decoder 50 ' and, without waiting for an I-frame or waiting for a video decode buffer to be filled, it decodes the received intra-coded frames so that they are sent to the user of the receiving device without much delay 20 ' are displayed. Furthermore, the receiving device receives 20 ' already from the 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 up.

3c shows a representation of a server according to the invention 10 and receiving devices according to the invention 20 . 20 ' in the state of receiving the stream of inter-coded frames of the requested video signal after the switching operation. Once in the video buffer 30 of the receiving device 20 ' there are enough frames for decoding, these are sent to the decoder 50 ' over the first decoder input 55 ' forwarded so that they are then decoded. The receiver 20 ' signals the server 10 preferably over the device 80 ' that enough frames of the stream 31.1 are available from inter-coded frames and thus no intra-coded frames are needed anymore. Thereupon, or due to the passage of a predetermined time T, the transmission of the intra-coded frames by the server 10 set.

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. A big advantage is experienced by the user of the receiving device 20 ' in this example, however, no visible delay in the display of the requested video signal.

4 shows a diagram of a switching operation without measures to reduce the switching delay. In a first state (encircled "1") are in a receiving device 20 the decoded frames derived from a stream of inter-coded frames 21 a previously requested video signal 12 , in this case z. B. TV channel "17" the user in one step 190 displayed. In one step 121 then this channel is left "17" and it should be on the channel "8", that is the video signal 11 to be switched. Upon exiting channel "17", the image frame of channel "17" stops and after a user and network delay, waiting for an I-frame of the stream begins 31 respectively. 31.1 with the inter-coded frames. As soon as an I-frame occurs, the receiving device starts 20 , the inter-coded frames in the video buffer 30 of the receiving device 20 to save (step 151 ). Depending on the type of encoding and order of the frames, in the worst case, a whole group of pictures must be in the video buffer 30 of the receiving device 20 saved, causing a delay 313 in the worst case leads. Only then can a display of the decoded image frames 21 done and then the user in one step 140 which state is displayed 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 switchover delay occurs 310 of more than one group of pictures, in the worst case about 2000 ms on. The users and network delay 311 is based z. On packet loss, jitter ping times, users etc.

5 shows a schematic of a switching operation using the transmitting and receiving method according to the invention. The starting point is again the state indicated by the encircled "1" as well as in 4 , In the server 10 At any given time, at least one intra-coded frame will be generated 52 of the requested video signal 11 maintained. This is from the stream 31 respectively. 31.1 of the video signal 11 created, which is why the intra-coded frames 52 of the stream 51 at the worst case decoding delay 313 are shown delayed. After expiration of a user and network delay 311 becomes the first intra-coded frame 52 to the receiving device 20 Posted. There, this is after a decoding delay 314 in case of a Intra-coded frames 52 decoded and displayed. Thus, the system is in state "2" (encircling "2"), in which the user decoded image frames 21 are displayed from a stream 51 from intra-coded frames 52 come. In parallel, the receiver stores 20 inter coded frames in one step 151 in a video buffer 30 , As soon as there are enough inter-coded frames (indicated by a decoding delay 313 ) starts the decoding of the inter-coded frames, which then out of the stream instead of the decoded image frames 51 are displayed. stream 51 is then no longer necessary and will be turned off. This puts the system in state "3" (encircled "3").

By applying this method, the total switching delay becomes 310 minimized to a maximum delay of only two frames (about 80 ms). No matter what time the user switches from one channel to the other channel, this time delay is minimized (random zapping).

6 shows a schematic of a switching operation using the inventive transmission and reception method, wherein additionally a bridging sequence 33 is sent and received. After leaving the channel "17", the transmission of intra-coded frames takes place on the one hand again 52 of a stream 51 , In addition, via a burst transmission, the video buffer is bridged at a frequency 33 , in this case a complete group of pictures, filled faster than normal (step 152 ). Alternatively or in combination, the video buffer is populated quickly in the step 152 also due to a reduced quality and thus a reduced data volume of the bridging sequence 33 , The decoding delay 313.1 the bridging sequence 33 is shortened compared to the decoding delay of a normal transmitted sequence of inter-coded pictures because the bridging sequence 33 faster in the buffer of the receiving device 20 arrives. However, even during this shortened decoding delay 313.1 already the decoded image frames 21 from the stream 51 from intra-coded frames 52 displayed. Once the bridging sequence 33 is present in the video buffer and is decodable, this is decoded and displayed to the user. From this moment is the sending of the stream 51 from intra-coded frames 52 no longer necessary, because now a decoding and displaying is possible solely because of the inter-coded frames.

The switchover delay 310 is a total of only a maximum of two frames (about 80 ms), but the stream 51 from intra-coded frames 52 no longer for such a long duration as in the example 5 Posted. 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, especially digital television signals significantly 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 account of a channel request preferably by sending not only inter-coded frames but also in parallel also intra-coded frames to the receiving device. 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. In this case, a higher bandwidth is required only for a short period of time, since 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. Due to the statistical distribution of the switching times of many different users, the higher bandwidth occupancy during a switchover on average will not bring any crassly 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 requires even less additional bandwidth and, overall, all the processes necessary for this are completed within an even shorter time. reference numeral 10 server 11 video signal 12 Other, previously requested video signal 20 receiving set 21 picture frame 30 video buffer 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 bridge sequence 33.1 Group of Pictures 40 Video decoder of the server 45 Device 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 from intra-coded frames 52 Intra-coded frame 52.2 Lost Intra-coded Frame 55 First entrance 56 Second entrance 60 headend 70 coaxial cable 80 Device for sending an access request 90 Device 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 121 Leaving another, previously requested video signal 130 Decoding the at least one intra-coded frame to at least one image frame 131 Connecting to the video signal over the stream with inter-coded frames 132 Connecting to the video signal over the stream of intra-coded frames 140 Display the at least one decoded image frame from the stream of intra-coded frames 150 Receive an inter-coded frame of a stream with inter-coded frames of the video signal 151 Storing inter-coded frames in the video buffer 152 Save the bypass sequence to the video buffer 160 Determine if there are enough inter-coded frames for decoding 170 Decode the existing inter-coded frames to image frames 180 Display the decoded image frames from the stream with inter-coded frames 190 Displaying at least one decoded frame of another previously requested video signal 200 Receiving an access request for the video signal 210 Transmitting at least one intra-coded frame of a stream of intra-coded frames of the video signal 220 Transmitting at least one inter-coded frame of a stream with inter-coded frames of the video signal 221 Sending a bridge sequence with inter-coded frames using a burst transmission over a unicast connection 230 Determine if a time T has expired or if there is an acknowledgment message from the receiver of the stream of intra-coded frames 240 Stop sending the stream out of intra-coded frames 250 Transmitting at least one inter-coded frame of a stream with inter-coded frames of another previously requested video signal 300 access request 310 switching delay 311 User and network delay 312 Delay waiting for an intra-coded frame of a stream with inter-coded frames and decoding time 313 Decoding delay in the worst case 313.1 Decoding delay of the bridging sequence 314 Decoding delay in the case of an intra-coded frame

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• "Analysis of zapping times and IP-TV" by Peter Siebert at al. [0003]
• Peter Siebert et al. [0004]

Claims (17)

Transmission method for transmitting a digital, originally inter-coded video signal ( 11 ) to a receiving device ( 20 ), comprising the following steps, in a server ( 10 ): - receiving ( 200 ) an access request ( 300 ) with respect to the video signal ( 11 ); - send ( 210 ) at least one intra-coded frame ( 52 ) of a stream ( 51 ) from intra-coded frames ( 52 ) of the video signal ( 11 ). A transmission method according to claim 1, additionally comprising the steps of: - 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 whether an acknowledgment message from the receiving device ( 20 ) is present; if a time T has expired or if a confirmation message is present: - Stop ( 240 ) of sending the stream ( 51 ) from intra-coded frames ( 52 ). 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 ). Transmission method according to one of the preceding claims, additionally comprising the steps: - buffering of the at least one inter-coded frame of the stream ( 31 ) with inter-coded frames of the video signal ( 11 ) in a cache; - reading a bridging sequence ( 33 ) with inter-coded frames from the buffer, the bridging sequence ( 33 ) begins with an intra-coded frame. - send ( 221 ) of the bridging sequence ( 33 ) with inter-coded frames by means of a burst transmission over a unicast connection to the receiving device ( 20 ). Transmission method according to one of the preceding claims, wherein the following step is performed first: - transmission ( 250 ) at least one inter-coded frame of a stream ( 31 ) with inter-coded frames of another previously requested video signal ( 12 ). Receiving method for delay-free reception of 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 ); - send ( 110 ) of the access request ( 300 ) to the server ( 10 ); - Receive ( 120 ) at least one intra-coded frame ( 52 ) of a stream ( 51 ) from intra-coded frames of the video signal ( 11 ) from the server ( 10 ); - decode ( 130 ) of the at least one intra-coded frame ( 52 ) to at least one image frame ( 21 ); - Show ( 140 ) of the at least one decoded image frame ( 21 ) from the stream ( 51 ) from intra-coded frames. Receiving method according to claim 6, additionally comprising 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 into a video buffer ( 30 ); - Determine ( 160 ), whether there are enough inter-coded frames for decoding; if there are sufficient inter-coded frames for decoding, additionally comprising the steps of: decoding ( 170 ) of the existing inter-coded frames to image frames ( 21 ); - Show ( 180 ) of the decoded image frames ( 21 ) from the stream ( 31 ) with inter-coded frames and preferably - sending a confirmation message to the server ( 10 ). Receiving method according to claims 6 to 7, additionally comprising the steps: - receiving a bridging sequence ( 33 ) with inter-coded frames by means of a burst transmission over a unicast connection to the server ( 10 ), where the bridging sequence ( 33 ) begins with an intra-coded frame. - To save ( 152 ) of the bridging sequence ( 33 ) into the video buffer ( 30 ). A receiving method according to any one of claims 6 to 8, wherein first the following step is performed: - displaying ( 190 ) at least one image frame ( 21 ) of another previously requested video signal ( 12 ). Receiver ( 20 ) for the low-delay reception of 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 ) An institution ( 80 ) for sending an access request ( 300 ) with respect to the video signal ( 11 ) to the server ( 10 ) and the video decoder ( 50 ) a second input ( 56 ) for receiving intra-coded frames ( 52 ) of a stream ( 51 ) from intra-coded frames ( 52 ) having. Receiver ( 20 ) according to claim 10, additionally comprising means for determining the decodability of inter-coded frames in the video buffer ( 30 ). Receiver ( 20 ) according to one of claims 10 to 11, wherein the device ( 80 ) for sending an access request ( 300 ) is additionally set up, a confirmation message to the server ( 10 ) as soon as frames with inter-coded frames in the video buffer ( 30 ) are decodable. Server ( 10 ) for transmitting a digital, originally inter-coded video signal ( 11 ) to a receiving device ( 20 ), characterized in that, the server ( 10 ) at least one institution ( 90 ) for receiving an access request ( 300 ) with respect to the video signal ( 11 ) and at least one device ( 45 ) for transmitting at least one intra-coded frame ( 52 ) of a stream ( 51 ) from intra-coded frames ( 52 ) of the video signal ( 11 ). Server ( 10 ) according to claim 13, additionally comprising at least one video decoder ( 40 ) with a video buffer ( 30 ), the video decoder ( 40 ) with the device ( 45 ) for transmitting at least one intra-coded frame ( 52 ) of a stream ( 51 ) from intra-coded frames ( 52 ) connected is. Server ( 10 ) according to claims 13 to 14, wherein the device ( 90 ) for receiving an access request ( 300 ) is additionally set up, a confirmation message from the receiving device ( 20 ) and / or determine the expiration of a time period T. Server ( 10 ) according to claim 13 to 15, wherein the server ( 10 ) in a cable headend ( 60 ) is arranged. Server ( 10 ) according to claim 13 to 16 or receiving device ( 20 ) according to claim 10 to 12, wherein the server ( 10 ) and the receiving device ( 20 ) via a coaxial cable network ( 70 ) are connected.

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