FLV封装结构
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2022-03-21 08:01:44
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FLV
结构
FLV header
/*
An FLV file shall begin with the FLV header:
FLV header
----------------------------------------------------------------------
Field Type Comment
----------------------------------------------------------------------
Signature UI8 Signature byte always 'F' (0x46)
Signature UI8 Signature byte always 'L' (0x4C)
Signature UI8 Signature byte always 'V' (0x56)
Version UI8 File version (for example, 0x01 for FLV version 1)
TypeFlagsReserved UB [5] Shall be 0
TypeFlagsAudio UB [1] 1 = Audio tags are present
TypeFlagsReserved UB [1] Shall be 0
TypeFlagsVideo UB [1] 1 = Video tags are present
DataOffset UI32 The length of this header in bytes
The DataOffset field usually has a value of 9 for FLV version 1. This field is present to accommodate larger headers
in future versions.
*/
FLV Tag
/*
FLV Tag
The FLV tag contains metadata for audio, video, or scripts, optional encryption metadata, and the payload.
----------------------------------------------------------
Field Type Comment
-----------------------------------------------------------
Reserved UB [2] Reserved for FMS, should be 0
Filter UB [1] Indicates if packets are filtered.
0 = No pre-processing required.
1 = Pre-processing (such as decryption) of the packet is
required before it can be rendered.
Shall be 0 in unencrypted files, and 1 for encrypted tags.
See Annex F. FLV Encryption for the use of filters.
TagType UB [5] Type of contents in this tag. The following types are
defined:
8 = audio
9 = video
18 = script data
DataSize UI24 Length of the message. Number of bytes after StreamID to
end of tag (Equal to length of the tag – 11)
Timestamp UI24 Time in milliseconds at which the data in this tag applies.
This value is relative to the first tag in the FLV file, which
always has a timestamp of 0.
TimestampExtended UI8 Extension of the Timestamp field to form a SI32 value. This
field represents the upper 8 bits, while the previous
Timestamp field represents the lower 24 bits of the time in
milliseconds.
StreamID UI24 Always 0.
AudioTagHeader IF TagType == 8 AudioTagHeader element as defined in Section E.4.2.1.
AudioTagHeader
VideoTagHeader IF TagType == 9 VideoTagHeader element as defined in Section E.4.3.1.
VideoTagHeader
EncryptionHeader IF Filter == 1 Encryption header shall be included for each protected
EncryptionTagHeader sample, as defined in Section F.3.1.
FilterParams IF Filter == 1 FilterParams shall be included for each protected sample, as
FilterParams defined in Section F.3.2.
Data IF TagType == 8 AUDIO DATA Data specific for each media type
IF TagType == 9 VIDEOD ATA
IF TagType == 18SCRIPTDATA
*/
Audio Tag Header
/*
Audio tags are similar to the DefineSound tag in the SWF file format.
For formats also supported in SWF, the payload data is identical in FLV and SWF.
----------------------------------------------------------------------------------------------------
Field Type Comment
----------------------------------------------------------------------------------------------------
SoundFormat UB [4] Format of SoundData. The following values are defined:
0 = Linear PCM, platform endian
(See notes following 1 = ADPCM
table, for special 2 = MP3
encodings) 3 = Linear PCM, little endian
4 = Nellymoser 16 kHz mono
5 = Nellymoser 8 kHz mono
6 = Nellymoser
7 = G.711 A-law logarithmic PCM
8 = G.711 mu-law logarithmic PCM
9 = reserved
10 = AAC
11 = Speex
14 = MP3 8 kHz
15 = Device-specific sound
Formats 7, 8, 14, and 15 are reserved.
AAC is supported in Flash Player 9,0,115,0 and higher.
Speex is supported in Flash Player 10 and higher.
SoundRate UB [2] Sampling rate. The following values are defined:
0 = 5.5 kHz
1 = 11 kHz
2 = 22 kHz
3 = 44 kHz
SoundSize UB [1] Size of each audio sample. This parameter only pertains to
uncompressed formats. Compressed formats always decode
to 16 bits internally.
0 = 8-bit samples
1 = 16-bit samples
SoundType UB [1] Mono or stereo sound
0 = Mono sound
1 = Stereo sound
AACPacketType IF SoundFormat == 10 The following values are defined:
UI8 0 = AAC sequence header
1 = AAC raw
*/
Video Tag Header
/*
The VideoTagHeader contains video-specific metadata.
---------------------------------------------------------------------
Field Type Comment
---------------------------------------------------------------------
Frame Type UB [4] Type of video frame. The following values are defined:
1 = key frame (for AVC, a seekable frame)
2 = inter frame (for AVC, a non-seekable frame)
3 = disposable inter frame (H.263 only)
4 = generated key frame (reserved for server use only)
5 = video info/command frame
CodecID UB [4] Codec Identifier. The following values are defined:
2 = Sorenson H.263
3 = Screen video
4 = On2 VP6
5 = On2 VP6 with alpha channel
6 = Screen video version 2
7 = AVC
AVCPacketType IF CodecID == 7 The following values are defined:
UI8 0 = AVC sequence header
1 = AVC NALU
2 = AVC end of sequence (lower level NALU sequence ender is
not required or supported)
CompositionTime IF CodecID == 7 IF AVCPacketType == 1
SI24 Composition time offset
ELSE
0
*/
FLV File Body
/*
The FLV File Body
After the FLV header, the remainder of an FLV file shall consist of alternating back-pointers and tags.
They interleave as shown in the following table:
---------------------------------------------------------------
Field Type Comment
---------------------------------------------------------------
PreviousTagSize0 UI32 Always 0
Tag1 FLVTAG First tag
PreviousTagSize1 UI32 Size of previous tag, including its header, in bytes. For FLV version
1, this value is 11 plus the DataSize of the previous tag.
Tag2 FLVTAG Second tag
...
PreviousTagSizeN-1 UI32 Size of second-to-last tag, including its header, in bytes.
TagN FLVTAG Last tag
PreviousTagSizeN UI32 Size of last tag, including its header, in bytes.
---------------------------------------------------------------
*/
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