Methods and systems for preventing start code emulation at locations that include non-byte aligned and/or bit-shifted positions

• US 20040030665A1
• Filed: 04/18/2003
• Published: 02/12/2004
• Est. Priority Date: 04/19/2002
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Sullivan, Gary J.
• Granted Patent: US 7,248,740 B2
• Time in Patent Office: Days
• US Class Current: 706/48
• CPC Class Codes: H04J 3/0605 Special codes used as synchronising signal
• CPC Class Codes: H04N 19/00 Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
• CPC Class Codes: H04N 19/70 characterised by syntax aspects related to video coding, e.g. related to compression standards
• CPC Class Codes: H04N 19/89 involving methods or arrangements for detection of transmission errors at the decoder

Abstract

Methods and systems provide approaches to start code emulation prevention at a granularity higher than the bit level. In various embodiments, start code emulation prevention can occur at locations other than data boundaries such as byte boundaries and the like. These embodiments can be used in connection with systems that do not always preserve data alignment boundaries in the data that is processed. In some systems, the described techniques can provide a basis from which decoder systems can recover in the event that data boundaries are lost.

Claims

1. A method comprising:

searching for at least one pattern of fixed-size data portions within data that is intended for encoding in an environment using start codes, individual fixed-size data portions comprising at least two bits;

responsive to finding one or more patterns, inserting start code emulation prevention data relative to the data that contains the pattern; and

wherein said searching and said inserting are designed to prevent emulation at one or more location that does not start at a data boundary.

2. The method of claim 1, wherein the act of searching is performed by searching video data.

3. The method of claim 1, wherein the act of searching is performed by searching audio data.

4. The method of claim 1, wherein the act of searching is performed by searching audio/video data.

5. The method of claim 1, wherein the act of searching is performed by searching for one or more patterns, at least one of which comprises at least two fixed-size data portions.

6. The method of claim 1, wherein the act of inserting the start code emulation prevention data comprises inserting more than one bit.

7. The method of claim 1, wherein the act of searching is performed by searching for multiple patterns.

8. The method of claim 1, wherein the act of searching is performed by searching for multiple patterns at least some of which have different lengths.

9. The method of claim 1, wherein the act of searching is performed by searching for multiple patterns, individual patterns being structured as a prefix followed by a type-indication suffix.

10. The method of claim 1, wherein the act of searching is performed by searching for multiple patterns, individual patterns being structured as a prefix followed by a type-indication suffix, wherein one or more of each pattern'"'"'s prefix length and type-indication suffix can differ in length from prefix lengths and type-indication suffix lengths of other patterns.

11. The method of claim 1, wherein the act of inserting start code emulation prevention data comprises selecting from among multiple different patterns of emulation prevention data.

12. The method of claim 1, wherein the act of inserting start code emulation prevention data comprises selecting from among multiple different patterns of emulation prevention data individual ones of which can have different lengths.

13. The method of claim 1, wherein the act of inserting the start code emulation prevention data comprises inserting an amount of data is that equal in number of bits to an individual fixed-size data portion.

14. The method of claim 1 further comprising transmitting data that contains start code emulation prevention data.

15. The method of claim 1, wherein the acts of searching and inserting are performed by an encoder.

16. One or more computer-readable media embodying an encoder that is configured to perform a method comprising:

searching for at least one pattern of fixed-size data portions within data that is intended for encoding in an environment using start codes, individual fixed-size data portions comprising at least two bits;

responsive to finding one or more patterns, inserting start code emulation prevention data relative to the data that contains the pattern; and

wherein said searching and said inserting are designed to prevent emulation at one or more location that does not start at a data boundary.

17. One or more computer-readable media embodying instructions which, when executed by one or more processors, cause the one or more processors to perform a method comprising:

searching for at least one pattern of fixed-size data portions within data that is intended for encoding in an environment using start codes, individual fixed-size data portions comprising at least two bits;

responsive to finding one or more patterns, inserting start code emulation prevention data relative to the data that contains the pattern; and

wherein said searching and said inserting are designed to prevent emulation at one or more location that does not start at a data boundary.

18. The computer-readable media of claim 17, wherein the instructions cause the one or more processors to perform said searching and said inserting on video data.

19. The computer-readable media of claim 17, wherein the instructions cause the one or more processors to perform said searching and said inserting on audio data.

20. The computer-readable media of claim 17, wherein the instructions cause the one or more processors to perform said searching and said inserting on audio/video data.

21. The computer-readable media of claim 17, wherein the instructions cause the one or more processors to search for a pattern comprising at least two fixed-size data portions.

22. The computer-readable media of claim 17, wherein the instructions cause the one or more processors to insert start code emulation prevention data comprising more than one bit.

23. The computer-readable media of claim 17, wherein the instructions cause the one or more processors to search for multiple patterns.

24. The computer-readable media of claim 17, wherein the instructions cause the one or more processors to search for multiple patterns at least some of which have different lengths.

25. The computer-readable media of claim 17, wherein the instructions cause the one or more processors to search for multiple patterns, individual patterns being structured as a prefix followed by a type-indication suffix.

26. The computer-readable media of claim 17, wherein the instructions cause the one or more processors to search for multiple patterns, individual patterns being structured as a prefix followed by a type-indication suffix, wherein one or more of each pattern'"'"'s prefix length and type-indication suffix can differ in length from prefix lengths and type-indication suffix lengths of other patterns.

27. The computer-readable media of claim 17, wherein the instructions cause the one or more processors to insert start code emulation prevention data by selecting from among multiple different patterns of emulation prevention data.

28. The computer-readable media of claim 17, wherein the instructions cause the one or more processors to insert start code emulation prevention data by selecting from among multiple different patterns of emulation prevention data individual ones of which can have different lengths.

29. The computer-readable media of claim 17, wherein the instructions cause the one or more processors to insert an amount of data is that equal in number of bits to an individual fixed-size data portion.

30. The computer-readable media of claim 17, wherein the instructions cause the one or more processors to transmit data that contains start code emulation prevention data.

31. A method comprising:

searching for at least one byte-level pattern within data that is intended for encoding in an environment using start codes, the pattern being defined by multiple bytes;

responsive to finding one or more patterns, inserting start code emulation prevention data relative to the data that contains the pattern; and

wherein said searching and said inserting are designed to prevent emulation at one or more location that does not start at a byte boundary.

32. The method of claim 31, wherein the act of searching is performed by searching video data.

33. The method of claim 31, wherein the act of searching is performed by searching audio data.

34. The method of claim 31, wherein the act of searching is performed by searching audio/video data.

35. The method of claim 31, wherein the act of inserting the start code emulation prevention data comprises inserting at least one byte.

36. The method of claim 31 further comprising transmitting data that contains start code emulation prevention data.

37. The method of claim 31, wherein the acts of searching and inserting are performed by an encoder.

38. One or more computer-readable media embodying an encoder that is configured to perform a method comprising:

searching for at least one byte-level pattern within data that is intended for encoding in an environment using start codes, the pattern being defined by multiple bytes;

responsive to finding one or more patterns, inserting start code emulation prevention data relative to the data that contains the pattern; and

wherein said searching and said inserting are designed to prevent emulation at one or more location that does not start at a byte boundary.

39. One or more computer-readable media embodying instructions which, when executed by one or more processors, cause the one or more processors to perform a method comprising:

searching for at least one byte-level pattern within data that is intended for encoding in an environment using start codes, the pattern being defined by multiple bytes;

responsive to finding one or more patterns, inserting start code emulation prevention data relative to the data that contains the pattern; and

wherein said searching and said inserting are designed to prevent emulation at one or more location that does not start at a byte boundary.

40. A method comprising:

receiving data that has been encoded with start code emulation prevention data to prevent emulation of one or more start codes at locations that include those that do not start at a data boundary, individual instances of the start code emulation prevention data comprising multiple bits;

searching for legitimate start codes within the decoded data;

searching the received data to identify start code emulation prevention data; and

responsive to finding the start code emulation prevention data, removing the start code emulation prevention data.

41. The method of claim 40, wherein the act of receiving is performed by receiving video data.

42. The method of claim 40, wherein the act of receiving is performed by receiving audio data.

43. The method of claim 40, wherein the act of receiving is performed by receiving audio/video data.

44. The method of claim 40, wherein the recited acts are performed by a decoder.

45. One or more computer systems programmed to implement the method of claim 40.

46. One or more computer-readable media embodying a decoder that is configured to:

receive data that has been encoded with start code emulation prevention data to prevent emulation of one or more start codes at locations that include those that do not start at a data boundary, individual instances of the start code emulation prevention data comprising multiple bits;

search for legitimate start codes within the received data;

search the received data to identify start code emulation prevention data; and

responsive to finding the start code emulation prevention data, remove the start code emulation prevention data.

47. A method comprising:

receiving data that has been encoded with start code emulation prevention data to prevent emulation of start codes, individual instances of the start code emulation prevention data comprising one or more bytes, at least one instance of the start code emulation prevention data being designed to prevent emulation of a start code that is starting at a location that is not a byte boundary;

searching for legitimate start codes within the received data;

searching the received data to identify start code emulation prevention data;

responsive to finding the start code emulation prevention data, removing the start code emulation prevention data.

48. The method of claim 47, wherein the act of receiving is performed by receiving video data.

49. The method of claim 47, wherein the act of receiving is performed by receiving audio data.

50. The method of claim 47, wherein the act of receiving is performed by receiving audio/video data.

51. One or more computer-readable media embodying instructions which, when executed by one or more processors, cause the one or more processors to implement the method of claim 47.

52. A decoder configured to:

receive data that has been encoded with start code emulation prevention data to prevent emulation of start codes, individual instances of the start code emulation prevention data comprising one or more bytes, at least one instance of the start code emulation prevention data being designed to prevent emulation of a start code that is starting at a location that is not a byte boundary;

search for legitimate start codes within the received data;

search the received data to identify start code emulation prevention data; and

responsive to finding the start code emulation prevention data, remove the start code emulation prevention data.

53. One or more computer systems embodying the decoder of claim 52.

54. A method comprising:

shifting at least a portion of a start code multiple times relative to one or more data boundaries;

identifying one or more characteristic pattern within the start code portion such that at least one of the characteristic patterns occurs for every shifted position relative to at least one data boundary; and

using the characteristic pattern(s) as a search pattern for conducting start code emulation prevention data insertion to prevent start code emulation at non-data-boundary-aligned locations.

55. The method of claim 54, wherein said portion of the start code that is shifted comprises a start code prefix.

56. The method of claim 54, wherein said portion of the start code that is shifted comprises a start code prefix, wherein the start code prefix comprises N bytes having a first value, followed by at least one other byte having a second value that is different from the first value, where N is greater than or equal to 1.

57. The method of claim 54, wherein said portion of the start code that is shifted comprises a start code prefix, wherein the start code prefix comprises N bytes having a first value, followed by at least one other byte having a second value that is different from the first value, wherein the first value equals 0x00, where N is greater than or equal to 1.

58. The method of claim 54, wherein said portion of the start code that is shifted comprises a start code prefix, wherein the start code prefix comprises N bytes having a first value, followed by at least one other byte having a second value that is different from the first value, wherein the second value equals 0x01, where N is greater than or equal to 1.

59. The method of claim 54, wherein said portion of the start code that is shifted comprises a start code prefix, wherein the start code prefix comprises N bytes having a first value, followed by one byte having a second value that is different from the first value, where N=2.

60. The method of claim 54, wherein said portion of the start code that is shifted comprises a start code prefix, wherein the start code prefix comprises N bytes having a first value, followed by one byte having a second value that is different from the first value, where N=2 and the first value equals 0x00.

61. The method of claim 54, wherein said portion of the start code that is shifted comprises a start code prefix, wherein the start code prefix comprises N bytes having a first value, followed by one byte having a second value that is different from the first value, where N=2 and the second value equals 0x01.

62. The method of claim 54 further comprising inserting start code emulation prevention data at data boundary locations responsive to finding the characteristic pattern within a data stream.

63. The method of claim 54 further comprising inserting emulation prevention data in a data stream responsive to identifying a pattern within the data stream that emulates data that has had emulation prevention data already inserted.

64. One or more computer-readable media having computer-readable instructions thereon which, when executed by one or more processors, cause the one or more processors to implement the method of claim 54.

65. A system embodying the one or more computer-readable media of claim 64.

66. A method comprising:

searching for one or more a first patterns within a data stream, the one or more first patterns being characterized as matching only a portion of a start code prefix at locations in the data stream that include at least one location that is not at the start of a data boundary;

responsive to finding one of the one or more first patterns, replacing the first pattern with a first replacement pattern effective to prevent emulation of the value of one or more start codes;

searching for one or more second patterns within the data stream, the one or more second patterns being characterized as matching only a portion of a start code that has been processed to prevent start code emulation;

responsive to finding one of the one or more second patterns, replacing the second pattern with a second replacement pattern effective to prevent emulation of a start code emulation prevention pattern.

67. The method of claim 66, wherein the acts of searching and replacing are designed to prevent emulation of start codes at non-data-boundary-aligned locations.

68. The method of claim 66, wherein the patterns are defined in terms of bytes of data.

69. The method of claim 66, wherein the one or more first pattern is characterized as N bytes having a first value, and the first replacement pattern is characterized as N−

1 bytes having the first value, followed by an emulation prevention byte having a different value, followed by a byte having the first value, where N is greater than or equal to 2.

70. The method of claim 66, wherein the one or more second pattern is characterized as N−

1 bytes having a first value, followed by a byte having an emulation prevention byte value, and the one or more second replacement pattern is characterized as N−

1 bytes having the first value, followed by an emulation prevention byte having the emulation prevention byte value, followed by a byte having the emulation prevention byte value, where N is greater than or equal to 2.

71. The method of claim 66, wherein:

the one or more first pattern is characterized as N bytes having a first value, and the first replacement pattern is characterized as N−

1 bytes having the first value, followed by a emulation prevention byte having an emulation prevention byte value, followed by a byte having the first value; and

the one or more second pattern is characterized as N−

1 bytes having the first value, followed by a byte having the emulation prevention byte value, and the one or more second replacement pattern is characterized as N−

1 bytes having the first value, followed by an emulation prevention byte having the emulation prevention byte value, followed by a byte having the emulation prevention byte value.

72. The method of claim 66, wherein:

the one or more first pattern is characterized as N bytes having a first value, and the first replacement pattern is characterized as N−

1 bytes having the first value, followed by an emulation prevention byte having an emulation prevention byte value, followed by a byte having the first value; and

the one or more second pattern is characterized as N−

1 bytes having the first value, followed by a byte having the emulation prevention byte value, and the second replacement pattern is characterized as N−

1 bytes having the first value, followed by a emulation prevention byte having the emulation prevention byte value, followed by a byte having the emulation prevention byte value, wherein N=2.

73. One or more computer-readable media having computer-readable instructions thereon which, when executed by one or more processors, cause the one or more processors to implement the method of claim 66.

74. A system embodying the one or more computer-readable media of claim 73.

75. A method comprising:

receiving data that has been processed to contain start code emulation prevention data to prevent emulation of start codes, the data being in a format equivalent to the processing of data to be transmitted in an environment using start codes that has been processed in accordance with a rule that;

searches for one or more first pattern within a data stream, the one or more first pattern being characterized as matching only a portion of a start code at locations in the data stream that include at least one location that is not at the start of a data boundary;

responsive to finding one of the one or more first pattern, replaces the first pattern with a first replacement pattern effective to prevent emulation of the value of one or more start codes;

searches for one or more second pattern within the data stream, the one or more second pattern being characterized as matching only a portion of a start code that has been processed to prevent start code emulation; and

responsive to finding one of the one or more the second pattern, replaces the second pattern with a second replacement pattern effective to prevent emulation of the first replacement pattern;

searching for legitimate start codes within the received data;

searching the received data to identify start code emulation prevention data; and

responsive to finding start code emulation prevention data, removing the start code emulation prevention data.

76. The method of claim 75, wherein the searching and replacing of said rule is designed to prevent emulation of start codes at non-data-boundary-aligned locations.

77. The method of claim 75, wherein the patterns are defined in terms of bytes of data.

78. The method of claim 75, wherein the one or more first pattern is characterized as N bytes having a first value, and the first replacement pattern is characterized as N−

1 bytes having the first value, followed by an emulation prevention byte having a different value, followed by a byte having the first value, where N is greater than or equal to 2.

79. The method of claim 75, wherein one or more second pattern is characterized as N−

1 bytes having a first value, followed by a byte having an emulation prevention byte value, and the one or more second replacement pattern is characterized as N−

1 bytes having the first value, followed by an emulation prevention byte having the emulation prevention byte value, followed by a byte having the emulation prevention byte value, wherein N is greater than or equal to 2.

80. The method of claim 75, wherein:

the one or more first pattern is characterized as N bytes having a first value, and the first replacement pattern is characterized as N−

1 bytes having the first value, followed by an emulation prevention byte having an emulation prevention byte value, followed by a byte having the first value; and

the one or more second pattern is characterized as N−

1 bytes having the first value, followed by a byte having the emulation prevention byte value, and the one or more second replacement pattern is characterized as N−

1 bytes having the first value, followed by an emulation prevention byte having the emulation prevention byte value, followed by a byte having the emulation prevention byte value.

81. The method of claim 75, wherein:

the one or more first pattern is characterized as N bytes having a first value, and the first replacement pattern is characterized as N−

1 bytes having the first value, followed by an code prevention emulation byte having an emulation prevention byte value, followed by a byte having the first value; and

the one or more second pattern is characterized as N−

1 bytes having the first value, followed by a byte having the emulation prevention byte value, and the second replacement pattern is characterized as N−

1 bytes having the first value, followed by an emulation prevention byte having the emulation prevention byte value, followed by a byte having the emulation prevention byte value, wherein N=2.

82. A method comprising processing a data stream that is intended for encoding in an environment using start codes in a manner that is effective to prevent start code emulation at one or more bit-shifted positions by searching for and manipulating only byte-level patterns.

83. One or more computer-readable media having instructions which, when executed by one or more processors cause the one or more processors to implement the method of claim 82.

84. A system embodying the one or more computer-readable media of claim 83.

85. An encoder configured to implement the method of claim 82.

86. A method comprising:

receiving a data stream;

processing the data stream effective to;

provide start codes having different lengths;

prevent bit-shifted emulation of start codes having longer lengths; and

prevent only data-boundary-aligned emulation of start codes having shorter lengths.

87. The method of claim 86 further comprising processing data of the data stream by using longer start codes less frequently than shorter start codes.

88. The method of claim 86, wherein prevention of bit-shifted emulation of start codes having longer lengths is effective to provide for data boundary alignment recovery in the event that boundary recovery is lost.

89. One or more computer-readable media having instructions which, when executed by one or more processors cause the one or more processors to implement the method of claim 86.

90. A system embodying the one or more computer-readable media of claim 89.

91. An encoder configured to implement the method of claim 86.

92. A method comprising:

searching for one or more first pattern within a data stream, the one or more first pattern being characterized as matching at least a portion of a start code associated with a first start code having a first length;

responsive to finding the one or more first pattern, replacing the one or more first pattern with a first replacement pattern effective to prevent start code emulation of the first start code at byte-aligned positions;

searching for one or more second pattern within the data stream, the one or more second pattern being characterized as matching only a portion of a second start code associated with a second start code having a second length that is longer than the first length;

responsive to finding the one or more second pattern, replacing the second pattern with a second replacement pattern effective to prevent start code emulation of the second start code at non-byte aligned positions;

searching for one or more third pattern within the data stream, the one or more third pattern being characterized as matching data that has been processed to prevent start code emulation; and

responsive to finding the one or more third pattern, replacing the one or more third pattern with a third replacement pattern effective to distinguish between data that has been processed to prevent start code emulation and data that naturally happens to resemble data that has been processed to prevent start code emulation.

93. The method of claim 92, wherein the patterns are defined in terms of bytes.

94. The method of claim 92, wherein the one or more first pattern is characterized as N bytes having a first value followed by a byte having a second value, and the first replacement pattern is characterized as N bytes having the first value, followed by a start code emulation prevention byte having a different value, followed by a byte having the second value.

95. The method of claim 92, wherein the one or more second pattern is characterized as N+1 bytes having a first value, and the second replacement pattern is characterized as N bytes having the first value, followed by a start code emulation prevention byte having a different value, followed by a byte having the first value.

96. The method of claim 92, wherein the one or more third pattern is characterized as N bytes having a first value followed by a byte having an emulation prevention byte value, and the third replacement pattern is characterized as N bytes having the first value, followed by two start code emulation prevention bytes having the emulation prevention byte value.

97. The method of claim 92, wherein:

the one or more first pattern is characterized as N bytes having a first value followed by a byte having a second value, and the first replacement pattern is characterized as N bytes having the first value, followed by a start code emulation prevention byte having a start code emulation prevention byte value, followed by a byte having the second value;

the one or more second pattern is characterized as N+1 bytes having the first value, and the second replacement pattern is characterized as N bytes having the first value, followed by a start code emulation prevention byte having the start code emulation prevention byte value, followed by a byte having the first value; and

the one or more third pattern is characterized as N bytes having the first value followed by a byte having the start code emulation prevention byte value, and the third replacement pattern is characterized as N bytes having the first value, followed by two start code emulation prevention bytes having the start code emulation prevention byte value.

98. The method of claim 92, wherein the acts of replacing the first, second and third patterns comprise inserting into the individual respective patterns an emulation prevention byte having a value.

99. The method of claim 92, wherein the acts of replacing the first, second and third patterns comprise inserting into the individual respective patterns an emulation prevention byte having a value, wherein the last byte of the first start code or start code prefix and the last byte of the second start code or start code prefix differ in value from the value of the emulation prevention byte by the value of one bit.

100. The method of claim 92, wherein the first, second and third replacement patterns differ in value as between each pattern'"'"'s two least significant bits.

101. The method of claim 92, wherein the first, second and third replacement patterns differ in value only between the value of the two least significant bits of the last byte.

102. The method of claim 92, wherein the first, second and third replacement patterns differ in value as between each pattern'"'"'s two least significant bits, a fourth value of the two least significant bits that does not correspond to the first, second, or third replacement patterns being used for a purpose other than as ordinary data.

103. The method of claim 102 further comprising:

searching for a fourth pattern, the fourth pattern being characterized as matching the remaining value of the two bits that differ in value in the first, second and third patterns, and

responsive to finding the fourth pattern, replacing the fourth pattern with a fourth replacement pattern effective to provide a consistent behavior for all patterns that differ in the value of the two bits that differ in value for the other three search patterns.

104. The method of claim 92 further comprising padding space after the end of a data payload with bytes having a pre-determined value without inserting emulation prevention bytes between padding values.

105. One or more computer-readable media having computer-readable instructions thereon which, when executed by one or more processors, cause the one or more processors to implement the method of claim 92.

106. A system embodying the one or more computer-readable media of claim 105.

107. An encoder configured to implement the method of claim 92.

108. A method comprising:

receiving data that has been processed to contain start code emulation prevention data to prevent emulation of start codes, the encoded data being in a format equivalent to the processing of data to be transmitted in an environment using start codes that has been processed in accordance with a rule that;

searches for one or more first pattern within a data stream, the one or more first pattern being characterized as matching at least a portion of a start code associated with a first start code having a first length;

responsive to finding the one or more first pattern, replaces the first pattern with a first replacement pattern effective to prevent start code emulation of the first start code at byte-aligned positions;

searches for one or more second pattern within the data stream, the one or more second pattern being characterized as matching only a portion of a second start code associated with a second start code having a second length that is longer than the first length;

responsive to finding the one or more second pattern, replaces the one or more second pattern with a second replacement pattern effective to prevent start code emulation of the second start code at non-byte aligned positions;

searches for one or more third pattern within the data stream, the one or more third pattern being characterized as matching data that has been processed to prevent start code emulation;

responsive to finding the one or more third pattern, replaces the one or more third pattern with a third replacement pattern effective to distinguish between data that has been processed to prevent start code emulation and data that naturally happens to resemble data that has been processed to prevent start code emulation;

searching for legitimate start codes within the received data;

searching the received data to identify start code emulation prevention data; and

responsive to finding start code emulation prevention data, removing the start code emulation prevention data.

109. The method of claim 108, wherein the patterns are defined in terms of bytes.

110. The method of claim 108, wherein the patterns are defined in terms of bytes, the act of searching for legitimate start codes comprising searching for a start code having a longer length and responsive to finding said longer length start code, recovering byte alignment.

111. The method of claim 108, wherein the patterns are defined in terms of bytes, the act of searching for legitimate start codes comprising searching for a start code having a longer length and responsive to finding said longer length start code, recovering byte alignment, and further comprising after recovering byte alignment, searching for start codes having shorter lengths than the length of the start code having the longer length.

112. The method of claim 108, wherein the one or more first pattern is characterized as N bytes having a first value followed by a byte having a second value, and the first replacement pattern is characterized as N bytes having the first value, followed by a start code emulation prevention byte having a different value, followed by a byte having the second value.

113. The method of claim 108, wherein the one or more second pattern is characterized as N+1 bytes having a first value, and the second replacement pattern is characterized as N bytes having the first value, followed by a start code emulation prevention byte having a different value, followed by a byte having the first value.

114. The method of claim 108, wherein the one or more third pattern is characterized as N bytes having a first value followed by a byte having an emulation prevention byte value, and the third replacement pattern is characterized as N bytes having the first value, followed by two start code emulation prevention bytes having the emulation prevention byte value.

115. The method of claim 108, wherein:

the one or more first pattern is characterized as N bytes having a first value followed by a byte having a second value, and the first replacement pattern is characterized as N bytes having the first value, followed by a start code emulation prevention byte having a start code emulation prevention byte value, followed by a byte having the second value;

the one or more second pattern is characterized as N+1 bytes having the first value, and the second replacement pattern is characterized as N bytes having the first value, followed by a start code emulation prevention byte having the start code emulation prevention byte value, followed by a byte having the first value; and

the one or more third pattern is characterized as N bytes having the first value followed by a byte having the start code emulation prevention byte value, and the third replacement pattern is characterized as N bytes having the first value, followed by two start code emulation prevention bytes having the start code emulation prevention byte value.

116. The method of claim 108, wherein the first, second and third replacement patterns comprise the respective first, second and third patterns with an emulation prevention byte having been inserted therein, and wherein the last byte of the first start code or start code prefix and the last byte of the second start code or the start code prefix different in value from the value of the emulation prevention byte by the value of one bit.

117. The method of claim 108, wherein the first, second and third replacement patterns differ in value as between each pattern'"'"'s two least significant bits.

118. One or more computer-readable media having computer-readable instructions thereon which, when executed by one or more processors, cause the one or more processors to implement the method of claim 108.

119. A system embodying the one or more computer-readable media of claim 118.

120. A method comprising:

searching for a pattern within a data stream, the pattern being characterized as matching (a) a portion of a start code, and (b) at least a portion of multiple replacement patterns for other respective patterns;

responsive to finding the pattern that is searched for, replacing the searched-for pattern with a replacement pattern effective to prevent start code emulation for all shifted positions.

121. A method comprising:

searching for a pattern within a data stream, the pattern being characterized as matching (a) a portion of a start code prefix, and (b) at least a portion of multiple replacement patterns for other respective patterns;

responsive to finding the pattern that is searched for, replacing the searched-for pattern with a replacement pattern effective to prevent start code emulation for all shifted positions.