Method for fast channel change and corresponding device
In a video delivery environment where a channel change in an audio/video receiver starts with a burst delivery of an audio/video stream to the receiver, characteristics of the audio/video stream are determined such as audio-video drift and burst characteristics in terms of duration of excess data delivery. At least one of these characteristics determines an offset to add to an initialization of a decoder clock, so that moving images are shown as early as possible after receipt of the channel change command, to be joined by lip synchronized audio before burst end.
1. A method for fast channel change of an audio/video receiver device receiving an audio/video stream over an Internet Protocol network, wherein the method is implemented by said audio/video receiver device, the method comprising:
receiving a channel change command;
transmitting a request for burst delivery of said audio/video stream corresponding to a new channel;
initializing a decoder clock in said audio/video receiver device with a value of a last Program Clock Reference comprised in said burst delivery before receipt of a video Presentation Time Stamp comprised in said burst delivery plus an offset, wherein said offset is a function of a drift between video frames and corresponding audio frames in said burst and of a duration of excess data delivery of said burst delivery defined as a duration of a part of said burst delivery during which data is received in excess compared to a delivery at playout rate; and
receiving said audio/video stream at said playout rate after end of said burst delivery.
2. The method according to claim 1 , wherein said drift is a difference between said video Presentation Time Stamp and said last Program Clock Reference.
3. The method according to claim 1 , wherein said offset is equal to said drift if said difference is inferior to said duration of excess data delivery of said burst delivery and wherein said offset is said duration of excess data delivery otherwise.
4. The method according to claim 1 , further comprising:
monitoring said drift between audio and video frames; and
if said drift between audio and video frames changes, reinitializing said decoder clock based on said change in drift between audio and video frames.
5. The method according to claim 1 , further comprising:
monitoring burst characteristics; and
if said burst characteristics change, reinitializing said decoder clock based on said changed burst characteristics.
6. The method according to claim 1 , further comprising monitoring of said drift between audio and video frames and monitoring of burst characteristics, and reinitializing said decoder clock if said drift or said burst characteristics change, based on said changed drift or based on said changed burst characteristics.
7. The method according to claim 4 , wherein said reinitialization of said decoder clock is done before appearance of moving images are output by said audio/video receiver device.
8. The method according to claim 1 , wherein said decoder clock is a System Time Clock.
9. An audio/video receiver device comprising:
an interface configured to receive a channel change command;
a network interface configured to transmit a request for burst delivery of audio/video content from a selected audio/video channel; and
a processor and a memory configured to initialize a decoder clock of the audio/video receiver device with a value of a last program clock reference received before receipt of a video presentation time stamp plus an offset, wherein said offset is a function of a drift between audio and video frames in a burst delivery and of a duration of excess data delivery of said burst delivery defined as a duration of a part of said burst delivery during which data is received in excess compared to a delivery at playout rate; and
said network interface being further configured to switch to reception of audio/video content from a transmission at playout rate before end of said burst delivery.
10. The audio/video receiver device according to claim 9 , wherein said processor is further configured to compute said drift as a difference between said video Presentation Time Stamp and said last Program Clock Reference.
11. The audio/video receiver device according to claim 9 , wherein said processor is further configured to compute said offset as being equal to said drift if said difference is inferior to said duration of excess data delivery of said burst reception and wherein said offset is said duration of excess data delivery otherwise.
12. The audio/video receiver device according to claim 9 , wherein said processor is further configured to:
monitor said drift between audio and video frames; and
if said drift between audio and video frames changes, reinitialize said decoder clock based on said change in drift between audio and video frames.
13. The audio/video receiver device according to claim 9 , wherein said processor is further configured to:
monitor burst characteristics; and
if said burst characteristics change, reinitialize said decoder clock based on said changed burst characteristics.
14. The audio/video receiver device according to claim 9 , wherein said processor is further configured to monitor said drift between audio and video frames and to monitor burst characteristics, and to reinitialize said decoder clock if said drift or said burst characteristics change, based on said changed drift or based on said changed burst characteristics.
15. The audio/video receiver device according to claim 12 , wherein said processor is further configured to reinitialize said decoder clock before appearance of moving images are output by said audio/video receiver device.
16. The audio/video receiver device according to claim 9 , wherein said decoder clock is a System Time Clock.