Constant bitrate media encoding techniques

• US 7,383,180 B2
• Filed: 07/18/2003
• Issued: 06/03/2008
• Est. Priority Date: 07/18/2003
• Status: Expired due to Fees

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Thumpudi, Naveen, Chen, Wei-Ge
• Primary Examiner(s): MCFADDEN, SUSAN IRIS
• Application Number:
  US10/622,822
• Publication Number:
  US 20050015259A1
• Time in Patent Office: 1,782 Days
• Field of Search: 704/229
• US Class Current: 704/229
• CPC Class Codes: G10L 19/24 Variable rate codecs, e.g. for generating different qualities using a scalable representation such as hierarchical encoding or layered encoding

Abstract

CBR control strategies provide constant or relatively constant bitrate output with variable quality. The control strategies include various techniques and tools, which can be used in combination or independently. For example, an audio encoder uses a trellis in two-pass or delayed-decision CBR encoding. The trellis nodes are states derived by quantizing buffer fullness values. The transitions between nodes of a previous stage and nodes of a current stage depend on encoding a current chunk of audio at different quality levels. When pruning the trellis, the encoder uses a cost function that considers smoothness in quality as well as quality in absolute terms. The encoder may store compressed data at different quality levels, then output the compressed data after simplification of the trellis to a suitable point. If the two-pass or delayed-decision CBR encoding fails, the encoder uses one-pass CBR encoding for the sequence or part of the sequence.

Claims

1. In an audio encoder, a computer-implemented method of audio encoding according to a control strategy, the method comprising:

receiving a sequence of audio data;

encoding the sequence of audio data using a trellis to produce a bitstream of encoded audio data at constant or relatively constant bitrate, wherein the trellis include plural transitions, and wherein each of the plural transitions corresponds to an encoding of a chunk of plural samples of the audio data at a quality level, and wherein the encoding includes pruning the trellis according to a cost function that considers smoothness of quality changes; and

outputting the bitstream of encoded audio data.

2. The method of claim 1 wherein the cost function also considers noise to excitation ratio.

3. The method of claim 1 wherein the cost function considers both quality and the smoothness of quality changes.

4. The method of claim 1 further comprising:

storing encoded data for each of plural chunks encoded at each of plural quality levels;

determining a trace through the sequence, wherein the trace includes a determination of a selected quality level for each of the plural chunks; and

stitching together parts of the stored encoded data for the sequence along the trace to produce the bitstream.

5. The method of claim 1 wherein the encoding is two-pass encoding.

6. The method of claim 1 wherein the encoding is delayed-decision encoding.

7. The method of claim 6 wherein the encoding includes simplifying the trellis according to one or more criteria, if necessary, as the trellis exits a latency window, wherein the one or more criteria are based upon a candidate node exiting the latency window and one or more current nodes that descend from the candidate node.

8. The method of claim 1 wherein the trellis includes plural nodes based upon quantization of buffer fullness levels.

9. The method of claim 8 wherein the buffer fullness levels are for a virtual decoder buffer.

10. The method of claim 8 wherein the buffer fullness levels are for an encoder buffer.

11. The method of claim 8 wherein the quantization is adaptive depending on range of the buffer fullness levels.

12. The method of claim 1 wherein the outputting is to a persistent storage medium.

13. The method of claim 1 wherein the outputting is to a network connection.

14. The method of claim 1 wherein the outputting begins before the encoding ends.

15. A storage medium storing computer-executable instructions for causing a computer system programmed thereby to perform the method of claim 1.

16. In a media encoder, a computer-implemented method of media encoding according to a control strategy, the method comprising:

receiving a sequence of media data;

in a first pass, encoding the sequence of media data using a trellis to determine a trace through the sequence of media data, wherein the media data includes plural portions, and wherein the trace includes a determination of a quality level for each of the plural portions of the media data;

in a second pass, encoding the sequence of media data along the trace to produce bitstream of encoded media data at constant or relatively constant bitrate; and

outputting the bitstream of encoded media data.

17. A storage medium storing computer-executable instructions for causing a computer system programmed thereby to perform the method of claim 16.

18. The method of claim 16 wherein each of the portions is a chunk of plural samples.

19. The method of claim 16 wherein the media data are audio data.

20. In a media encoder, a computer-implemented method of media encoding according to a control strategy, the method comprising:

receiving a sequence of media data;

encoding the sequence of media data using a trellis to produce a bitstream of encoded media data at constant or relatively constant bitrate, wherein the encoding includes pruning the trellis according to a cost function that considers smoothness in quality changes as well as quality according to noise to excitation ratio; and

outputting the bitstream of encoded media data.

21. A storage medium storing computer-executable instructions for causing a computer system programmed thereby to perform the method of claim 20.

22. The method of claim 20 wherein the media data are audio data.

23. In a media encoder, a computer-implemented method of media encoding according to a control strategy, the method comprising:

receiving the sequence of media data;

encoding a sequence of media data using a trellis to produce a bitstream of encoded media data at constant or relatively constant bitrate, wherein the encoding includes pruning the trellis according to a cost function that considers both quality and smoothness in quality changes; and

outputting the bitstream of encoded media data.

24. A storage medium storing computer-executable instructions for causing a computer system programmed thereby to perform the method of claim 23.

25. The method of claim 23 wherein the media data are audio data.

26. In a media encoder, a computer-implemented method of media encoding according to a control strategy, the method comprising:

receiving a sequence of media data;

encoding the sequence of media data, including encoding each of plural portions of the sequence at each of multiple different quality levels, wherein the encoding uses a trellis with plural nodes based upon quantization of buffer fullness levels, and wherein the quantization of the buffer fullness levels is adaptive during the encoding;

storing encoded data for the plural portions encoded at each of the multiple different quality levels;

determining a trace through the sequence of media data, wherein the trace includes a determination of a selected quality level for each of the plural portions;

stitching together parts of the stored encoded data for the sequence along the trace to produce a bitstream of encoded media data at constant or relatively constant bitrate; and

outputting the bitstream of encoded media data.

27. A storage medium storing computer-executable instructions for causing a computer system programmed thereby to perform the method of claim 26.

28. The method of claim 26 wherein the media data are audio data.

29. The method of claim 26 wherein the plural portions are for the entire sequence.

30. In a media encoder, a computer-implemented method of media encoding according to a control strategy, the method comprising:

receiving a sequence of media data;

selecting between a two-pass encoding mode and a delayed-decision encoding mode;

if the two-pass encoding mode is selected,

in a first pass, encoding the sequence of media data to determine coding decisions for the sequence of media data; and

in a second pass, encoding the sequence of media data using the coding decisions to produce a bitstream of encoded media data at constant or relatively constant bitrate;

if the delayed-decision encoding mode is selected, encoding the sequence of media data to produce the bitstream of encoded media data, including enforcing simplification of a trace through the sequence of media data, if necessary, outside of a window of allowable latency; and

outputting the bitstream of encoded media data.

31. A storage medium storing computer-executable instructions for causing a computer system programmed thereby to perform the method of claim 30.

32. The method of claim 30 wherein the media data are audio data.

33. The method of claim 30 wherein the encoding in the first pass uses a trellis, and wherein the coding decisions indicate transitions in the trellis.

34. The method of claim 30 wherein the encoding in the delayed-decision encoding mode uses a trellis.

35. In a media encoder, a computer-implemented method of media encoding according to a delayed-decision control strategy, the method comprising:

receiving a sequence of media data;

encoding the sequence of media data using a trellis to produce a bitstream of encoded media data at constant or relatively constant bitrate, wherein the encoding includes simplifying the trellis according to one or more criteria, if necessary, as the trellis exits a latency window, wherein the one or more criteria are based upon a candidate node exiting the latency window and one or more current nodes that descend from the candidate node; and

outputting the bitstream of encoded media data.

36. A storage medium storing computer-executable instructions for causing a computer system programmed thereby to perform the method of claim 35.

37. The method of claim 35 wherein the media data are audio data.

38. The method of claim 35 wherein the one or more criteria include average cost of the one or more current nodes.

39. The method of claim 35 wherein the one or more criteria include least cost of the one or more current nodes.

40. The method of claim 35 wherein the one or more criteria include count of the one or more current nodes.

41. In a media encoder, a computer-implemented method of media encoding according to a control strategy, the method comprising:

receiving a sequence of media data;

encoding the sequence of media data using a trellis to produce a bitstream of encoded media data at constant or relatively constant bitrate, wherein the trellis includes plural nodes based upon quantization of buffer fullness levels, and wherein the quantization of the buffer fullness levels is adaptive during the encoding; and

outputting the bitstream of encoded media data.

42. A storage medium storing computer-executable instructions for causing a computer system programmed thereby to perform the method of claim 41.

43. The method of claim 41 wherein the media data are audio data.

44. The method of claim 41 wherein the buffer fullness levels are for a virtual decoder buffer.

45. The method of claim 41 wherein the buffer fullness levels are for an encoder buffer.

46. The method of claim 41 wherein the quantization changes depending on range of the buffer fullness levels.

47. In a media encoder, a computer-implemented method of media encoding according to a control strategy, the method comprising:

receiving a sequence of media data;

performing either two-pass or delayed-decision encoding of the sequence of media data;

checking whether the encoding has succeeded and, if the encoding has not succeeded, performing one-pass encoding of at least part of the sequence; and

outputting a bitstream of encoded media data at constant or relatively constant bitrate.

48. A storage medium storing computer-executable instructions for causing a computer system programmed thereby to perform the method of claim 47.