Video Decoder with an Adjustable Video Clock

• US 20090109988A1
• Filed: 10/26/2007
• Published: 04/30/2009
• Est. Priority Date: 10/26/2007
• Status: Abandoned Application

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Wales, Richard T., Musunuri, Chowdhary, Mauchly, J. William, Mackie, David J.
• Application Number:
  US11/925,013
• Publication Number:
  US 20090109988A1
• Time in Patent Office: Days
• US Class Current: 370/412
• CPC Class Codes: G06F 3/14 Digital output to display device ; Cooperation and interconnection of the display device with other functional units
• CPC Class Codes: G06F 3/1454 involving copying of the display data of a local workstation or window to a remote workstation or window so that an actual copy of the data is displayed simultaneously on two or more displays, e.g. teledisplay
• CPC Class Codes: G09G 2340/02 Handling of images in compressed format, e.g. JPEG, MPEG
• CPC Class Codes: G09G 5/12 Synchronisation between the display unit and other units, e.g. other display units, video-disc players
• CPC Class Codes: H04L 12/1827 Network arrangements for conference optimisation or adaptation
• CPC Class Codes: H04N 19/132 Sampling, masking or truncation of coding units, e.g. adaptive resampling, frame skipping, frame interpolation or high-frequency transform coefficient masking
• CPC Class Codes: H04N 19/436 using parallelised computational arrangements
• CPC Class Codes: H04N 19/44 Decoders specially adapted therefor, e.g. video decoders which are asymmetric with respect to the encoder
• CPC Class Codes: H04N 19/587 involving temporal sub-sampling or interpolation, e.g. decimation or subsequent interpolation of pictures in a video sequence
• CPC Class Codes: H04N 19/61 in combination with predictive coding
• CPC Class Codes: H04N 21/23406 involving management of server-side video buffer
• 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 21/43072 of multiple content streams on the same device
• CPC Class Codes: H04N 21/44004 involving video buffer management, e.g. video decoder buffer or video display buffer

Abstract

A method, an apparatus, and logic encoded in a computer-readable medium to carry out a method. The method includes receiving packets containing compressed video information, storing the received packets in a buffer memory, timestamping the received packets according to an adjustable clock; and removing packets from the buffer for decoding and playout of the video information, the removing according to playback order and at a time determined by the adjustable clock. The method includes adjusting the adjustable clock from time to time according to a measure the amount of time that the packets reside in the buffer memory, such that time latency caused by the buffer memory is limited. An overrun or an underrun of the buffer memory is unlikely.

Claims

1. A method comprising:

receiving packets containing compressed video information for a time sequence of pictures;

storing the received packets in a buffer memory;

timestamping the received packets according to an adjustable clock to provide a timestamp of the received packets;

removing packets from the buffer for playout of the video information in the packets, the removing at a time determined by the adjustable clock; and

adjusting the adjustable clock from time to time according to a measure of the amount of time that the packets reside in the buffer memory,

such that time latency caused by the buffer memory is limited.

2. A method as recited in claim 1, further comprising decompressing the packets removed from the buffer so that the playout is of decompressed video.

3. A method as recited in claim 1, wherein the storing of the received packets is in order of arrival, and the removing of the packets for playout is in playback order, such that no physical playout buffer is required.

4. A method as recited in claim 1, wherein the compressed video information is compressed by a remote encoder operating according to a remote encoding clock, such that the adjustable clock becomes synchronized to the remote encoding clock.

5. A method as recited in claim 2, wherein the decompressing takes a substantially fixed amount of time.

6. A method as recited in claim 1, further comprising calculating the measure of the amount of time the packets that correspond to a picture reside in the buffer memory, the calculating using the timestamps of the received packets to determine a measure of the average amount of time that the packets that correspond to a picture reside in the buffer memory.

7. A method as recited in claim 6, wherein late packets that arrive after a pre-determined amount of time are not considered in the determining of the measure of the average amount of time.

8. A method as recited in claim 7, wherein the late packets are treated as missing packets, the method further comprising providing for playback packets containing empty video information in place of missing or late packets.

9. A method as recited in claim 6, wherein the adjusting of the adjustable clock is to maintain the average time packets are in the buffer memory at a pre-selected amount of time.

10. A method as recited in claim 9, wherein the pre-selected amount of time corresponds to more than one-half frame of video data but less than two frames of video data.

11. A method as recited in claim 9, wherein the adjusting of the adjustable clock includes adding or subtracting a predetermined frequency increment to speed-up or slow down the adjustable clock so that the measure of the average amount of time is closer to the pre-selected amount of time.

12. A method as recited in claim 9, wherein the adjusting occurs every pre-selected first number of packets.

13. A method as recited in claim 10, wherein the adjusting that occurs every first number of packets is according to a short term average of the time packets reside in the buffer memory, the method further comprising:

adjusting the adjustable clock according to a long term average measure of the amount of time that the packets that correspond to a picture reside in the buffer memory, the adjusting according to a long term average measure occurring every pre-selected second number of packets.

14. A method as recited in claim 1, wherein the video information includes high definition video data.

15. A method as recited in claim 14, wherein the video information is compressed by a method substantially conforming to one of the H.264/AVC coding standard, the AVS standard, or the VC-1 standard.

16. A method as recited in claim 1, wherein the adjusting of the adjustable clock is periodic at a settable period.

17. An apparatus comprising:

a network interface coupled to a network and operative to receive packets from the network, the received packets containing compressed video information for a time sequence of video frames;

a buffer memory coupled to the network interface and configured to store the received packets, the buffer memory having or coupled to output logic;

an adjustable clock;

a timestamper coupled to the adjustable clock and operative to timestamp the received packets according to the adjustable clock to provide a timestamp of the received packets;

a decoder coupled to the output logic of the buffer memory and to the adjustable clock, the decoder operative to output and decompress the video information from packets in the buffer memory that correspond to a picture and to generate a displayable output of the decompressed picture, wherein the removing of compressed video information from the buffer and generation of displayable output is according to the rate of the adjustable clock; and

a clock adjustment controller coupled to the adjustable clock and configured to adjust the rate of the adjustable clock according to a measure of the amount of time that the packets corresponding to a frame of video data resides in the buffer memory,

such that time latency caused by the buffer memory is limited.

18. An apparatus as recited in claim 17, wherein the storing of the received packets is in order of arrival, and the removing of the packets for decoding and playout is in playback order.

19. An apparatus as recited in claim 17, wherein the decoder requires a substantially fixed amount of time to decode the video information in a packet.

20. An apparatus as recited in claim 17, further comprising a time in buffer indicator operative to calculate the measure of the amount of time packets reside in the buffer memory, the calculating using the timestamps of the received packets to determine a measure of the average amount of time that the packets that correspond to a picture reside in the buffer memory.

21. An apparatus as recited in claim 20, wherein clock adjustment controller is configured to adjust the adjustable clock to maintain the average time packets spend in the buffer memory at a pre-selected amount of time.

22. An apparatus as recited in claim 20, wherein the adjusting of the adjustable clock includes adding or subtracting a predetermined frequency increment to speed-up or slow down the adjustable clock so that the measure of the average amount of time is closer to the pre-selected amount of time.

23. An apparatus as recited in claim 21, wherein the adjusting occurs every pre-selected first number of packets.

24. An apparatus as recited in claim 23, wherein the adjusting that occurs every first number of packets is according to a short term average of the time packets reside in the buffer memory, and wherein the clock adjustment controller further is configured to adjust the adjustable clock according to a long term average measure of the amount of time that the packets that correspond to a picture reside in the buffer memory, the adjusting according to a long term average measure occurring every pre-selected second number of packets.

25. A computer-readable medium encoded with computer-executable instructions that when executed by one or more processors cause an apparatus that includes the one or more processors to carry out method comprising:

receiving packets containing compressed video information for a time sequence of pictures;

storing the received packets in a buffer memory in order of arrival;

timestamping the received packets according to an adjustable clock to provide a timestamp of the received packets;

removing packets from the buffer for decoding and playout of the video information in the packets, the removing according to playback order and at a time determined by the adjustable clock;

decoding the packets removed such that the decoding is according to the adjustable clock; and

adjusting the adjustable clock from time to time according to a measure the amount of time that the packets reside in the buffer memory,

such that time latency caused by the buffer memory is limited.