Introduction to FLV documents

1. brief introduction

FLV yes Adobe A published format that can be used as a live broadcast or an on-demand package , The format is very simple , in FLVTAG There is a form of , And each of these TAG They all exist independently .

2.FLV Introduction to format standards

2.1FLV The file header

Field	Number of occupancy	explain
Signature field	8	character "F" （0x46）
Signature field	8	character "L" （0x4C）
Signature field	8	character "V" （0x56）
edition	8	Document version
Keep the tag type	5	Fixed for 0
Audio tag type	1	1 Show audio labels for
Keep the tag type	1	Fixed for 0
Video tag type	1	1 Show video tags for
Data migration	32	Bytes of this header

Here's what I opened FLV file , see 16 Hexadecimal data .

  According to the analysis in the above figure ：

• 3 The label of the byte ：“F”、“L”、“V”
• 1 Bytes of FLV Document version ：0x01
• 5 Bits reserved ：00000b
• 1 Bit audio mark bit ：1b
• 1 Bits reserved ：0b
• 1 Bit video marker bit ：1b
• 4 Byte header data offset ：0x00 00 00 09

2.2FLV File content format

FLV The contents of the document are as follows ：

Field	Type size	explain
the previous TAG Size	4 byte	Has always been a 0
TAG1	FLVTAG	first TAG
the previous TAG Size	4 byte	the previous TAG Byte size , Include TAG Of Header+Body,TAG Of Header The size is 11 byte , So for 11 byte +TAG Body Size
TAG2	FLVTAG	the second TAG
the previous TAG Size	4 byte	.........
.........	4 byte	.........

You can see in the table FLV The format of file content is mainly FLVTAG,FLVTAG In two parts TAGHeader+TAGBody.

As shown in the figure below , I showed an audio TAG, Can see header by 11 byte body by 4 byte , Followed by a 4 Byte size “ the previous TAG Size ”, Values for 15.

The table below for FLVTAG Format analysis of ：

Field	Type size	explain
Retain	2 position	by FMS Retain , by 0
Filter	1 position	It is mainly used to encrypt the contents of files 0： No preprocessing 1： Preprocessing
TAG type	5 position	0x08： Audio TAG 0x09： video TAG 0x12： Script data
data size	24 position	TAG Of DATA Size of section
Time stamp	24 position	Display time in milliseconds
Extended timestamp	8 position	Supplementary timestamp added for timestamp
flow ID	24 position	by 0
TAG Of Data		Audio and video media data

explain ：

The size of the timestamp takes 3 Bytes , The biggest expression is 0xFFFFFF(16777215) millisecond , Convert to seconds 16777 second , Approximately equal to 4.66 Hours , If you use FLV The format of , The timestamp used can be stored up to 4.66 Hours .

The extended timestamp size accounts for 1 Bytes , The maximum is 0xFF(255), The extended timestamp makes FLV The original timestamp has been extended , It's not limited to 4.66 Hours , It can also be stored longer , You can probably store 1193 Hours , about 50 God .

2.3VideoTag Data analysis

The data format is shown in the table below ：

Field	Type size	explain
The frame type	4 position	1： Keyframes 2：P or B frame 3： Applied only to H.263 4： Generate keyframes （ Server usage ） 5： Video information / Command frame
Code identification	4 position	2：Sorenson H.263 3：Screen Video 4：On2 VP6 5： belt Alpha The tunnel On2 VP6 6：Screen Video2 7：H.264
H.264 The package type of	When the code ID is H.264 Time occupation 1 Bytes	0：H.264 Of Sequence Header 1：NALU 2：H.264 Of Sequence end
CTS	When the code ID is H.264 Time occupation 3 Bytes	When encoding using B When the frame ,DTS and PTS It's not equal .CTS Used to represent PTS and DTS Difference between
Video data	Video data	Compressed video data

The detailed explanation is shown in the figure below ： Observe the structure on the right   tag data()

 

2.4AudioTag Data analysis

The data format is shown in the table below ：

Field	Type size	explain
Sound format	4 position	I won't list all the details ： List a few common 2：MP3 10：AAC 11：Speex
Audio sampling rate	2 position	0：5.5kHz 1：11kHz 2：22kHz 3：44kHz
Sample size	1 position	0：8 position 1：16 position
Audio type	1 position	0：Mono sound 1：Stereo sound
Audio package type	When the audio is AAC Occupy this byte ,1 Bytes	0：AAC Sequence Header 1：AAC raw data
Audio data		Specific encoded audio data

The detailed explanation is shown in the figure below ： Observe the structure on the right   tag data()

 2.5ScriptData Data analysis

ScriptData The common way to show is FLV Of MetaData, The data format stored inside is generally AMF data , The table below for ScriptData Storage format .

Field	Type size	explain
type	8 position	Different values represent AMF Different types of formats 0：Number 1：Boolean 2：String 3：Object 5：Null 6：Undefined 7：Reference 8：ECMA Array 9：Object end marker 10：Strict Array 11：Data 12：Long String
data

3.FLV View tools

FLV analysis FLV analysis FLV analysis FLV analysis FLV analysis FLV analysis FLV analysis FLV analysis FLV analysis FLV analysis FLV analysis FLV analysis -C++ Document resources -CSDN download