Video transcoder with bitstream look ahead for rate control and statistical multiplexing

• US 6,310,915 B1
• Filed: 11/20/1998
• Issued: 10/30/2001
• Est. Priority Date: 11/20/1998
• Status: Expired due to Fees

• Current Assignee: LSI Logic Corporation (Broadcom, Inc.)
• Original Assignee: Harmonic Incorporated
• Inventors: Wells, Aaron, Linzer, Elliot
• Primary Examiner(s): Kelley, Chris
• Assistant Examiner(s): VO, TUNG T
• Application Number:
  US09/196,812
• Time in Patent Office: 1,075 Days
• Field of Search: H04/B.166, H04/N.712, 348/405.1, 348/409.1, 348/410.1, 348/412.1, 348/415.1, 348/416.1, 348/419.1, 382/232, 382/236, 382/239, 370/538, 455/6.3, 375/240.01, 375/240.16, 375/240.17, 375/240.03
• US Class Current: 375/240.03
• CPC Class Codes: H04N 19/40 using video transcoding, i.e. partial or full decoding of a coded input stream followed by re-encoding of the decoded output stream
• CPC Class Codes: H04N 21/23406 involving management of server-side video buffer
• CPC Class Codes: H04N 21/23655 Statistical multiplexing, e.g. by controlling the encoder to alter its bitrate to optimize the bandwidth utilization
• CPC Class Codes: H04N 21/44004 involving video buffer management, e.g. video decoder buffer or video display buffer

Abstract

A method is provided for transcoding, i.e., decoding, and re-encoding, a previously encoded video signal, to a second encoded representation. A number k>1 of previously encoded pictures of the previously encoded video signal are received in a buffer. Each of the k previously encoded pictures in the buffer is scanned to gather information on each of the k previously encoded pictures. An encoding parameter is allocated to a first one of the k previously encoded pictures which precedes each other one of the k previously encoded pictures in encoded order of the previously encoded video signal. The encoding parameter is allocated based on the information gathered for each of the k previously encoded pictures. The first previously encoded picture is decoded to produce a decoded picture. The decoded picture is re-encoded to generate a re-encoded picture in a second encoded representation of the video signal. The re-encoding is performed in a fashion which depends on the encoding parameter allocated thereto. An apparatus is also disclosed for carrying out the method including a buffer, a scanner (for performing the scanning and allocating steps), a decoder and an encoder.

Claims

1. A method for transcoding a previously encoded video signal to a second encoded representation thereof comprising the steps of:

(a) receiving k>

1 previously encoded pictures of a previously encoded video signal in a buffer,

(b) scanning each of said k previously encoded pictures in said buffer to gather information on each of said k previously encoded pictures,

(c) allocating an encoding parameter to one of said k previously encoded pictures, which precedes each other one of said k previously encoded pictures in encoded order of said previously encoded video signal, based on said information gathered for each of said k previously encoded pictures,

(d) decoding said one previously encoded picture, to produce a decoded picture,

(e) re-encoding said decoded picture, to generate a re-encoded picture in a second encoded representation of said video signal, said re-encoding being performed in a fashion which depends on said encoding parameter allocated thereto,

(f) splicing an end of said previously encoded video signal together with a beginning of another encoded video signal for sequential transfer to said channel,

wherein said step (a) further comprises the step of storing a picture at an end of said previously encoded video signal and at least one picture at a beginning of said another video signal in said look ahead buffer,

wherein said step (c) further comprises the step of gathering information regarding said at least one encoded pictures at a beginning of said another encoded video signal and said picture at an end of said previously encoded video signal, and

wherein in step (e), said picture at an end of said previously encoded video signal is re-encoded in accordance with an encoding parameter allocated based on information gathered for said picture and for said pictures at a beginning of said another encoded video signal.

2. The method of claim 1 further comprising the steps of:

maintaining a model of a decoder buffer,

determining a budget of bits to be produced in re-encoding said decoded picture,

modifing said budget based on said encoding parameter, and

re-encoding said decoded picture to produce a number of bits which depends on said modified budget.

3. The method of claim 1 wherein said step of re-encoding further comprising the steps of:

altering a model of a decoder buffer to fill at a channel rate indicated by said encoding parameter, and

determining a budget of a number of bits to generate while re-encoding said decoded picture which avoids overflowing and underflowing said model of said decoder buffer.

4. The method of claim 1 further comprising the step of changing a resolution of said decoded picture in response to said encoding parameter prior to step (e).

5. The method of claim 1 further comprising the step of spatially low pass filtering said decoded picture, without changing a resolution of said picture, in response to said encoding parameter prior to step (e).

6. The method of claim 1 further comprising the step of modifying pixel data at a border of said decoded picture in response to said encoding parameter prior to step (e).

7. The method of claim 1 further comprising the step of temporally filtering said decoded picture depending on said encoding parameter prior to step (e).

8. The method of claim 1 further comprising the step of setting a field display code in measuring a complexity of said previously encoded pictures.

9. The method of claim 1 further comprising the step of re-encoding said decoded picture as a progressive picture or an interlaced picture depending on said encoding parameter.

10. The method of claim 1 further comprising the step of selectively including at least one of error-concealment motion vectors and slice headers in said re-encoded version of said decoding picture depending on said encoding parameter.

11. The method of claim 10 wherein said step of including comprises the step of retaining previously generated error concealment motion vectors.

12. The method of claim 11 wherein said step of including comprises the step of retaining previously generated slice headers.

13. The method of claim 1 further comprising the steps of adjusting an inter/intra decision function depending on said encoding parameter and motion compensating each macroblock of said decoded picture based on an affinity for intercoding said macroblock produced by evaluating said decision function.

14. The method of claim 1 further comprising the steps of adjusting an encoding mode decision function to change an affinity for selecting a particular encoding mode depending on said encoding parameter and encoding according to said particular encoding mode based on an affinity produced by evaluating said decision function.

15. The method of claim 1 further comprising the step of determining whether or not to choose the same encoding mode in re-encoding said decoded picture as was chosen to produce said one previously encoded picture based on said encoding parameter.

16. The method of claim 15 further comprising the step of if said decoded picture is an intra picture then always choosing said same macroblock encoding mode as was chosen to form said one previously encoded picture.

17. The method of claim 1 wherein said step (e) further comprises the step of selecting a picture type for encoding at least said decoded picture at an end of said previously encoded video signal.

18. The method of claim 1 wherein said gathered information pertains to a compressed representation of said previously encoded pictures.

19. The method of claim 1 wherein said gathered information indicates a compression efficiency of said previously encoded pictures.

20. The method of claim 1 wherein said gathered information indicates an encoding standard according to which each of said previously encoded pictures was encoded.

21. The method of claim 1 wherein said gathered information indicates one or more encoding parameters for each of said encoded pictures.

22. The method of claim 1 wherein said gathered information indicates a pre-compression characteristic of said previously encoded pictures.

23. The method of claim 1 wherein said step of scanning further comprises the step of:

(c1) at least partially decoding said previously encoded pictures.

24. The method of claim 23 wherein said step of scanning further comprises the step of:

(c2) re-encoding said at least partially decoded pictures.

25. The method of claim 1 further comprising the steps of allocating a first channel rate as said encoding parameter in step (c) and allocating a second channel rate for encoding a second video signal, a sum of said first and second allocated channel rates being less than or equal to a total channel rate of a channel to which said re-encoded video signal and said second video signal are transferred.

26. The method of claim 1 wherein said gathered information indicates a picture coding type for each of said previously encoded pictures.

27. The method of claim 1 wherein said gathered information indicates a total number of bits used to encode each of said previously encoded pictures.

28. The method of claim 1 wherein said gathered information indicates a total number of stuffing bits added to each of said previously encoded pictures.

29. The method of claim 1 wherein said gathered information indicates a total number of header bits of each of said previously encoded pictures.

30. The method of claim 1 wherein said gathered information indicates the number of bits used to represent variable length encoded data of macroblocks of said previously encoded pictures.

31. The method of claim 1 wherein said gathered information includes information indicating the number of bits used to represent variable length encoded data of macroblocks of said previously encoded pictures and information indicating the number of bits used to represent headers of such macroblocks.

32. The method of claim 1 wherein said gathered information indicates the field display code of each of said previously encoded pictures.

33. The method of claim 1 wherein said gathered information indicates the picture structure of each of said previously encoded pictures.

34. The method of claim 1 wherein said gathered information indicates the macroblock mode of macroblocks in each of said previously encoded pictures.

35. The method of claim 1 wherein said gathered information indicates the macroblock DCT format of macroblocks in each of said previously encoded pictures.

36. The method of claim 1 wherein said gathered information indicates the quantizer scale factor in each of said previously encoded pictures.

37. The method of claim 1 wherein said gathered information indicates the number of bits used to encode one or more selected portions of each of said previously encoded pictures.

38. The method of claim 1 wherein said gathered information indicates the quantizer scale factor in one or more selected portions of each of said previously encoded pictures.

39. The method of claim 1 wherein said gathered information indicates the motion vector ranges used in encoding said previously encoded pictures.

40. The method of claim 1 wherein said gathered information indicates encoded motion vectors of each of said previously encoded pictures.

41. The method of claim 1 wherein said gathered information indicates a number of bits used to encode at least one of error-concealment motion vectors and slice headers.

42. The method of claim 1 wherein said gathered information indicates the channel bit rate, as measured from a transport delivery of said previously encoded video signal.

43. An apparatus for transcoding a previously encoded video signal to a second encoded representation thereof comprising:

(a) a buffer for receiving k>

1 previously encoded pictures of a previously encoded video signal,

(b) a scanner for scanning each of said k previously encoded pictures in said buffer to gather information on each of said k previously encoded pictures, and for allocating an encoding parameter to one of said k previously encoded pictures, which precedes each other one of said k previously encoded pictures in encoded order of said previously encoded video signal, based on said information gathered for each of said k previously encoded pictures,

(c) a decoder for decoding said one previously encoded picture, to produce a decoded picture, and

(d) an encoder for re-encoding said decoded picture, to generate a re-encoded picture in a second encoded representation of said video signal, said re-encoding being performed in a fashion which depends on said encoding parameter allocated thereto,

wherein said apparatus is configured for splicing an end of said re-encoded video signal together with a beginning of another encoded video signal for sequential transfer to said channel,

wherein said buffer is also for storing a picture at an end of said re-encoded video signal and at least one picture at a beginning of said another video signal in said look ahead buffer,

wherein said scanner is also for gathering information regarding said at least one encoded pictures at a beginning of said another encoded video signal and said picture at an end of said previously encoded video signal, and

wherein said encoder is also for re-encoding said picture at an end of said previously encoded video signal in accordance with an encoding parameter allocated based on information gathered for said picture and for said at least one picture at a beginning of said another encoded video signal.

44. The apparatus of claim 43 wherein said encoder is also for maintaining a model of a decoder buffer, for determining a budget of bits to be produced in re-encoding said decoded picture, for modifying said budget based on said encoding parameter, and for re-encoding said decoded picture to produce a number of bits which depends on said modified budget.

45. The apparatus of claim 43 further comprising:

a statistics computer for altering a model of a decoder buffer to fill at a channel rate indicated by said encoding parameter,

said encoder also for determining a budget of a number of bits to generate while re-encoding said decoded picture which avoids overflowing and underflowing said model of said decoder buffer.

46. The apparatus of claim 43 wherein said encoder is also for changing a resolution of said decoded picture in response to said encoding parameter prior to re-encoding.

47. The apparatus of claim 43 wherein said encoder is also for spatially low pass filtering said decoded picture, without changing a resolution of said decoded picture in response to said encoding parameter prior to re-encoding.

48. The apparatus of claim 43 wherein said processor is also for modifying pixel data at a border of said decoded picture in response to said encoding parameter prior to re-encoding.

49. The apparatus of claim 43 wherein said encoder is also for temporally filtering said decoded picture depending on said encoding parameter prior to re-encoding said decoded picture.

50. The apparatus of claim 43 further comprising a statistics computer for setting a field display code in measuring a complexity of said previously encoded pictures.

51. The apparatus of claim 43 wherein said encoder is also for re-encoding said decoded picture as a progressive picture or an interlaced picture depending on said encoding parameter.

52. The apparatus of claim 43 wherein said encoder is also for selectively including at least one of error-concealment motion vectors and slice headers in said re-encoded version of said decoding picture depending on said encoding parameter.

53. The apparatus of claim 52 wherein said encoder is also for retaining previously generated error concealment motion vectors.

54. The apparatus of claim 52 wherein said encoder is also for retaining previously generated slice headers.

55. The apparatus of claim 43 wherein said encoder is also for adjusting an inter/intra decision function depending on said encoding parameter and for motion compensating each macroblock of said decoded picture based on an affinity for intercoding produced by evaluating said decision function.

56. The apparatus of claim 43 wherein said encoder is also for adjusting an encoding mode decision function to change an affinity for selecting a particular encoding mode depending on said encoding parameter and for encoding according to said particular encoding mode based on an affinity produced by evaluating said decision function.

57. The apparatus of claim 43 wherein said encoder is also for determining whether or not to choose the same encoding mode in re-encoding said decoded picture as was chosen to produce said one previously encoded picture based on said encoding parameter.

58. The apparatus of claim 57 wherein said encoder is also for, if said decoded picture is an intra picture then, always choosing said same macroblock encoding mode as was chosen to form said one previously encoded picture.

59. The apparatus of claim 43 wherein said encoder is also for selecting a picture type for encoding at least said decoded picture at an end of said previously encoded video signal.

60. The apparatus of claim 43 wherein said gathered information pertains to a compressed representation of said previously encoded pictures.

61. The apparatus of claim 43 wherein said gathered information indicates a compression efficiency of said previously encoded pictures.

62. The apparatus of claim 43 wherein said gathered information indicates an encoding standard according to which each of said previously encoded pictures was encoded.

63. The apparatus of claim 43 wherein said gathered information indicates one or more encoding parameters for each of said encoded pictures.

64. The apparatus of claim 43 wherein said gathered information indicates a pre-compression characteristic of said previously encoded pictures.

65. The apparatus of claim 43 wherein said scanner comprises a decoder for at least partially decoding said previously encoded pictures.

66. The apparatus of claim 43 wherein said scanner further comprises an encoder for re-encoding said at least partially decoded pictures.

67. The apparatus of claim 43 further comprising a statistics computer for allocating a first channel rate as said encoding parameter and allocating a second channel rate for encoding a second video signal, a sum of said first and second allocated channel rates being less than or equal to a total channel rate of a channel to which said re-encoded video signal and said second video signal are transferred.

68. The apparatus of claim 43 wherein said gathered information indicates a picture coding type for each of said previously encoded pictures.

69. The apparatus of claim 43 wherein said gathered information indicates a total number of bits used to encode each of said previously encoded pictures.

70. The apparatus of claim 43 wherein said gathered information indicates a total number of stuffing bits added to each of said previously encoded pictures.

71. The apparatus of claim 43 wherein said gathered information indicates a total number of header bits of each of said previously encoded pictures.

72. The apparatus of claim 43 wherein said gathered information indicates the number of bits used to represent variable length encoded data of macroblocks of said previously encoded pictures.

73. The apparatus of claim 43 wherein said gathered information includes information indicating the number of bits used to represent variable length encoded data of macroblocks of said previously encoded pictures and information indicating the number of bits needed to represent the headers of such macroblocks.

74. The apparatus of claim 43 wherein said gathered information indicates the field display code of each of said previously encoded pictures.

75. The apparatus of claim 43 wherein said gathered information indicates the picture structure of each of said previously encoded pictures.

76. The apparatus of claim 43 wherein said gathered information indicates the macroblock mode of macroblocks in each of said previously encoded pictures.

77. The apparatus of claim 43 wherein said gathered information indicates the macroblock DCT format of macroblocks in each of said previously encoded pictures.

78. The apparatus of claim 43 wherein said gathered information indicates the quantizer scale factor in each of said previously encoded pictures.

79. The apparatus of claim 43 wherein said gathered information indicates the number of bits used to encode one or more selected portions of each of said previously encoded pictures.

80. The apparatus of claim 43 wherein said gathered information indicates the quantizer scale factor in one or more selected portions of each of said previously encoded pictures.

81. The apparatus of claim 43 wherein said gathered information indicates the motion vector ranges used in encoding said previously encoded pictures.

82. The apparatus of claim 43 wherein said gathered information indicates encoded motion vectors of each of said previously encoded pictures.

83. The apparatus of claim 43 wherein said gathered information indicates a number of bits used to encode error-concealment motion vectors, slice headers or both.

84. The apparatus of claim 43 wherein said information indicates the channel bit rate, as measured from a transport delivery of said previously encoded video signal.