Robust method for recovering a program time base in MPEG-2 transport streams and achieving audio/video sychronization

• US 20030066094A1
• Filed: 09/29/2001
• Published: 04/03/2003
• Est. Priority Date: 09/29/2001
• Status: Abandoned Application

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Glim, Arno, Meenakshisundaram, Ramanathan, Mani, Murali, van der Schaar, Auke Sjoerd
• Application Number:
  US09/967,877
• Publication Number:
  US 20030066094A1
• Time in Patent Office: Days
• US Class Current: 725/151
• CPC Class Codes: H04N 21/4302 Content synchronisation processes, e.g. decoder synchronisation
• CPC Class Codes: H04N 21/4305 Synchronising client clock from received content stream, e.g. locking decoder clock with encoder clock, extraction of the PCR packets arrangements for synchronising receiver with transmitter by comparing receiver clock with transmitter clock H04L7/0012; arrangements for synchronising receiver with transmitter wherein the receiver takes measures against momentary loss of synchronisation H04L7/0083
• CPC Class Codes: H04N 21/4344 Remultiplexing of multiplex streams, e.g. by modifying time stamps or remapping the packet identifiers

Abstract

An internal system time clock within an MPEG-2 decoder is synchronized in frequency and optionally in phase, but not in value, to program clock reference time stamps within a received MPEG-2 transport stream. A demultiplexer separating audio and video packets from the transport stream modifies the decoding and presentation time stamps within such packets by at least an offset between the program clock reference time stamp values and the internal system time clock time before forwarding the packets to the audio and video decoders. Discontinuities in the program clock reference time stamp sequence automatically result in a change in the offset, such that the internal system time clock continues to increase monotonically and decoding and presentation time stamps within the packets are not suddenly invalidated.

Claims

1. A decoder comprising:

an internal system time clock having a frequency set by reference to a program clock reference signal within an audio/video broadcast stream but having a time independent of a value of the program clock reference signal; and

a demultiplexer extracting audio and video packets from the broadcast stream and modifying decoding and presentation time stamps within the audio and video packets utilizing at least an offset between the program clock reference signal value and the internal system time clock time.

2. The decoder as set forth in claim 1 wherein the offset automatically changes with changes to the program clock reference signal value.

3. The decoder as set forth in claim 2 wherein the modified decoding and presentation time stamps increase monotonically despite discontinuities in a sequence for the program clock reference signal value.

4. The decoder as set forth in claim 1 further comprising:

a frequency control unit receiving the program clock reference signal from the broadcast stream and setting a frequency for the internal system time clock based upon the program clock reference signal value without altering the time for the internal system time clock.

5. The decoder as set forth in claim 1 further comprising:

audio and video decoders each receiving the audio and video packets, respectively, containing the modified decoding and presentation time stamps from the demultiplexer and employing the internal system time clock time and the modified decoding and presentation time stamps within the audio and video packets to control rendering of content within the audio and video packets.

6. The decoder as set forth in claim 1 wherein the decoding and presentation time stamps as received within the audio and video packets are replaced with the offset between the program clock reference signal value and the internal system time clock time.

7. The decoder as set forth in claim 1 wherein the decoding and presentation time stamps as received within the audio and video packets are replaced with the offset between the program clock reference signal value and the internal system time clock time plus a value for processing and buffering delays.

8. A video receiver comprising:

an input for receiving an audio/video broadcast stream;

a video display and audio system, or one or more connections to a video display and audio system, for playback of audio and video content decoded from the audio/video broadcast stream; and

a decoder decoding the audio and video content from the audio/video broadcast stream for playback, the decoder comprising;

an internal system time clock having a frequency set by reference to a program clock reference signal within an audio/video broadcast stream but having a time independent of a value of the program clock reference signal; and

a demultiplexer extracting audio and video packets from the broadcast stream and modifying decoding and presentation time stamps within the audio and video packets utilizing at least an offset between the program clock reference signal value and the internal system time clock time.

9. The video receiver as set forth in claim 8 wherein the offset automatically changes with changes to the program clock reference signal value.

10. The video receiver as set forth in claim 9 wherein the modified decoding and presentation time stamps increase monotonically despite discontinuities in a sequence for the program clock reference signal value.

11. The video receiver as set forth in claim 8 wherein the decoder further comprises:

a frequency control unit receiving the program clock reference signal from the broadcast stream and setting a frequency for the internal system time clock based upon the program clock reference signal value without altering the time for the internal system time clock.

12. The video receiver as set forth in claim 8 wherein the decoder further comprises:

audio and video decoders each receiving the audio and video packets, respectively, containing the modified decoding and presentation time stamps from the demultiplexer and employing the internal system time clock time and the modified decoding and presentation time stamps within the audio and video packets to control rendering of content within the audio and video packets.

13. The video receiver as set forth in claim 8 wherein the decoding and presentation time stamps as received within the audio and video packets are replaced with the offset between the program clock reference signal value and the internal system time clock time.

14. The video receiver as set forth in claim 8 wherein the decoding and presentation time stamps as received within the audio and video packets are replaced with the offset between the program clock reference signal value and the internal system time clock time plus a value for processing and buffering delays.

15. A method of decoding an audio/video broadcast stream comprising:

setting a frequency for an internal system time clock by reference to a program clock reference signal within an audio/video broadcast stream while maintaining a time for the internal system time clock independent of a value of the program clock reference signal; and

extracting audio and video packets from the broadcast stream; and

modifying decoding and presentation time stamps within the audio and video packets utilizing at least an offset between the program clock reference signal value and the internal system time clock time.

16. The method as set forth in claim 15 further comprising:

automatically changing the modification to the decoding and presentation time stamps within the audio and video packets with changes to the program clock reference signal value.

17. The method as set forth in claim 16 further comprising:

increasing the modified decoding and presentation time stamps monotonically despite discontinuities in a sequence for the program clock reference signal value.

18. The method as set forth in claim 15 further comprising:

receiving the program clock reference signal from the broadcast stream; and

setting a frequency for the internal system time clock based upon the program clock reference signal value without altering the time for the internal system time clock.

19. The method as set forth in claim 15 further comprising:

receiving the audio and video packets containing the modified decoding and presentation time stamps at audio and video decoders, respectively; and

employing the internal system time clock time and the modified decoding and presentation time stamps within the audio and video packets to control rendering of content within the audio and video packets by the audio and video decoders.

20. The method as set forth in claim 15 wherein the step of modifying decoding and presentation time stamps within the audio and video packets utilizing at least an offset between the program clock reference signal value and the internal system time clock time further comprises one of:

replacing the decoding and presentation time stamps as received within the audio and video packets with the offset between the program clock reference signal value and the internal system time clock time; and

replacing the decoding and presentation time stamps as received within the audio and video packets with the offset between the program clock reference signal value and the internal system time clock time plus a value for processing and buffering delays.