codecs 组成
2016-04-22 16:35
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The
is specified by RFC 6381. Specifically, see section
3.3 for the meaning of
In the case of
H.264 video, and this is followed by a dot and three 2-digit hexadecimal numbers defined by the H.264 standard:
the byte containing the
(currently
and the
Some examples:
H.264 Constrained Baseline Profile Level 3
H.264 Main Profile Level 3
H.264 High Profile Level 3
These are also the second, third, and fourth bytes of the Sequence Parameter Set and the AVC Configuration Box in an MP4 file. You can dump these bytes using a program such as
Configuration) Box and the hexadecimal values for
and
As for
MPEG-4 audio. It is followed by a dot and a hexadecimal
which can be looked up on the MPEG4 registration site. If this hexadecimal value is
14496-3 Audio), it is followed by another dot and an audio object type in decimal. These are listed in the ISO/IEC 14496-3 standard and onWikipedia,
and correspond to the first 5 bits of the
(unless these bits equal 31, in which case add 32 to the next 6 bits).
AAC LC audio, which is what is usually used with H.264 HTML5 video.
For example,
codecsparameter
is specified by RFC 6381. Specifically, see section
3.3 for the meaning of
avc1and
mp4avalues.
In the case of
avc1.4D401E,
avc1indicates
H.264 video, and this is followed by a dot and three 2-digit hexadecimal numbers defined by the H.264 standard:
profile_idc
the byte containing the
constraint_setflags
(currently
constraint_set0_flagthrough
constraint_set5_flag,
and the
reserved_zero_2bits)
level_idc
Some examples:
avc1.42E01E:
H.264 Constrained Baseline Profile Level 3
avc1.4D401E:
H.264 Main Profile Level 3
avc1.64001E:
H.264 High Profile Level 3
These are also the second, third, and fourth bytes of the Sequence Parameter Set and the AVC Configuration Box in an MP4 file. You can dump these bytes using a program such as
mp4file:
mp4file --dump movie.mp4. Look for the
avcC(AVC
Configuration) Box and the hexadecimal values for
AVCProfileIndication,
profile_compatibility,
and
AVCLevelIndication.
As for
mp4a.40.2,
mp4aindicates
MPEG-4 audio. It is followed by a dot and a hexadecimal
ObjectTypeIndication(
objectTypeIdin
mp4fileoutput),
which can be looked up on the MPEG4 registration site. If this hexadecimal value is
40(ISO/IEC
14496-3 Audio), it is followed by another dot and an audio object type in decimal. These are listed in the ISO/IEC 14496-3 standard and onWikipedia,
and correspond to the first 5 bits of the
DecoderSpecificInfo(
decSpecificInfo)
(unless these bits equal 31, in which case add 32 to the next 6 bits).
mp4a.40.2indicates
AAC LC audio, which is what is usually used with H.264 HTML5 video.
For example,
codecs="avc1.42E01E, mp4a.40.2"would be correct for the movie below:
$ mp4file --dump movie.mp4 ... type avcC (moov.trak.mdia.minf.stbl.stsd.avc1.avcC) ◀━━ avc1 configurationVersion = 1 (0x01) AVCProfileIndication = 66 (0x42) ◀━━ 42 profile_compatibility = 224 (0xe0) ◀━━ E0 AVCLevelIndication = 30 (0x1e) ◀━━ 1E ... type esds (moov.trak.mdia.minf.stbl.stsd.mp4a.esds) ◀━━ mp4a version = 0 (0x00) flags = 0 (0x000000) ESID = 2 (0x0002) streamDependenceFlag = 0 (0x0) <1 bits> URLFlag = 0 (0x0) <1 bits> OCRstreamFlag = 0 (0x0) <1 bits> streamPriority = 0 (0x00) <5 bits> decConfigDescr objectTypeId = 64 (0x40) ◀━━ 40 streamType = 5 (0x05) <6 bits> upStream = 0 (0x0) <1 bits> reserved = 1 (0x1) <1 bits> bufferSizeDB = 0 (0x000000) <24 bits> maxBitrate = 78267 (0x000131bb) avgBitrate = 78267 (0x000131bb) decSpecificInfo info = <2 bytes> 11 90 |..| ◀━━ 2 (first 5 bits in decimal) ...
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