Analyze FLV format with rtmp play

Recently made a RTMP transit service program, through the practice, familiar with rtmp play and push in various formats, summarized here.

Program GitHub Address: Https://github.com/runner365/rtmp_relay

RTMP Play Receive Message analysis

Message received at first frame:

1) 0x46 4c: Refer to the following article:

Character FLV Header

2) 0x01 05

Version typeflagsreserved Typeflagsaudio typeflagsreserved typeflagsvideo

When this is resolved, it is generally not necessary to control

3) 0x00 00 00 09

FLV Header offset: That is, from the beginning of 9 bytes, is the FLV true message header.

4) 0x00 00 00 00

This is the 1th frame of the PREVIOUSTAGSIZE0 (front frame length), because it is the first frame, so it must be 0;

5) 0x08 can refer to the following text: Reference two, reference three

First byte at the beginning of the frame: 0x08 for audio, 0x09 for video

6) 0x00 00 04

Frame payload Length: Because the first frame of the audio is ASC, it is only 4 bytes.

7) 0x 00 00 00 00

Timestamp, time stamp

8) 0x 00 00 00

Streamid, Stream ID

9) 0x AF 00 13 90

The audio PAYLOAD:0XAF00 begins with ASC flag, and the 0xaf01 is followed by the real audio data

0x13 90, i.e. 0b0001 0011 1001 0000,

ASC flag format: xxxx xyyy yzzz z000

X characters: AAC type, 2 for AAC-LC,5 for SBR, 29 for ps,5 and 29 for special Ascflag will become 4;

Y-Character: sample rate, sample rates, 7 = 22050 sample Rate

Z Character: Number of channels, 2 is dual channel

0x xx 0F

This is still PreviousTagSize1, last frame length 15bytes

One) 0x09 video type, new frame

0x00 00 22

Video Frame payload Length

0x00 xx 0a 00

Time stamp: This place has a big pit, the order is: A[3] a[0] a[1] a[2], the last one is the highest bit.

) 0x00 00 00

Streamid, Stream ID.

0x 17 00

Video frame begins with 2 bytes:

0x17 00: Indicates that the content is SPS and PPS

0x17 01: Indicates that the content is I-frame

0X27: Indicates that the content is P-frame

16)

0000002bh:17 xx C0 1F FF E1 0E C0; ...... B??. GB?
0000003bh:1f 8C 8D F0 0F (6A)----(CE) 刯 ... h?
0000004BH:3C 80; <€

12th, 13 bytes: 0x00 0E is Spslen, which is 14 byte length

After skipping 14 bytes, 0x01 is the identity of the PPS start, skipping it.

0x00 04 is Ppslen, which is 4 bytes, and finally 0x68 CE 3c 80 is pps.

Reference:

1, the FLV header

	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 is present
Typeflagsreserved	UB [1]	shall be 0
Typeflagsvideo	UB [1]	1 = Video tags is present
Dataoffset	UI32	The length of this header in bytes

Signature: The first 3 bytes of the FLV file are fixed 'F'L'V', which identifies the file as an FLV format. When doing a format probe,

If the first 3 bytes are found to be "flv", it is considered to be an FLV file.

version: The 4th byte represents the FLV version number.

Flags: the No. 0 and 2nd digits of the 5th byte, respectively, indicate the presence of video and audio. (1 means present, 0 means not present)

Dataoffset : The last 4 bytes represent the length of the FLV header.

2,FLV Body Overall

Field	Type	Comment
PreviousTagSize0	UI32	Always 0
Tag1	Flvtag	First tag
PreviousTagSize1	UI32	Size of previous tag, including its header, in bytes. For FLV Version1, This value is one 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 it header, in bytes

After the FLV header , it is the flv File Body.

The FLV File Body is composed of a series of back-pointers + tags. The back-pointers is 4 bytes of data representing the size of the previous tag.

3,flv Body Details

Field	Type	Comment
Reserved	UB [2]	Reserved for FMS, should is 0
Filter	UB [1]	Indicates if packets is filtered. 0 = No pre-processing required. 1 = pre-processing (such as decryption) of the packet is Required before it can be rendered. Shall is 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 the this tag. The following types is Defined 8 = Audio 9 = Video = 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 "the data" this tag applies. This value was relative to the first tag in the FLV file, which Always have 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 bits of the time in Milliseconds.
Streamid	UI24	Always 0.
Audiotagheader	IF Tagtype = = 8 Audiotagheader
Videotagheader	IF Tagtype = = 9 Videotagheader
Encryptionheader	IF Filter = = 1 Encryptiontagheader
Filterparams	IF Filter = = 1 Filterparams
Data	IF Tagtype = = 8 Audiodata IF Tagtype = = 9 Videodata IF Tagtype = = 18 Scriptdata	Data specific for each media t

Analyze FLV format with rtmp play