一、简单介绍
FLV（Flash Video）是Adobe公司推出的一种媒体封装格式。一个FLV文件，每个Tag类型都属于一个流。也就是说一个
FLV文件最多只有一路音频流、一个路视频流，不能定义单个类型的多个独立流在一个文件中。
FLV数据以大端序存储，解析时需要注意。比如：0x12C，那么存储时就是0x01 0x2C。FLV封装格式由一个FLV Header
和FLV Body组成，其中FLV Body由很多个Tag组成。Tag一般可以分为三种类型：脚本数据类型、音频数据类型、视频数据
类型。
一个标准的FLV文件结构如下图所示：
FLV Header 官方协议文档定义如下：
46 4c 56 01 05 20 20 20 09 //就代表该FLV文件包含音频、视频
二、FLV文件Body
每一个tag其实是由两部分组成，Tag header(11 Byte+Tag data(实际数据域。Tag Header中存放着TagType、DataSize等
字段信息。而Tag data部分就是实际数据域信息，后面会分别讲述数据域(Tag data。
其中FLV tag官方文档定义如下：
2.2.1 Audio data tags（音频数据tag）
AudioSpecificConfig( {
audioObjectType = GetAudioObjectType(;
samplingFrequencyIndex; // 4 bslbf
if (samplingFrequencyIndex == 0xf {
samplingFrequency; // 24 uimsbf
}
channelConfiguration; // 4 bslbf
sbrPresentFlag = -1;
psPresentFlag = -1;
if (audioObjectType == 5 || audioObjectType == 29 {
// ...
}
else {
extensionAudioObjectType = 0;
}
switch (audioObjectType {
case 1: case 2: case 3: case 4: //...
GASpecificConfig(;
break:
case ...:
//...
}
if (extensionAudioObjectType != 5 && bits_to_decode( >= 16 {
//...
}
GetAudioObjectType( {
audioObjectType; // 5 uimsbf
if (audioObjectType == 31 {
audioObjectType = 32 + audioObjectTypeExt; // 6 uimsbf
}
return audioObjectType;
}
2.2.2 Video data tags（视频数据Tag）
VIDEODATA官方协议文档定义如下：
aligned(8 class AVCDecoderConfigurationRecord {
unsigned int(8 configurationVersion = 1;
unsigned int(8 AVCProfileIndication;
unsigned int(8 profile_compatibility;
unsigned int(8 AVCLevelIndication;
bit(6 reserved = '111111'b;
unsigned int(2 lengthSizeMinusOne;
bit(3 reserved = '111'b;
unsigned int(5 numOfSequenceParameterSets;
for (i = 0; i < numOfSequenceParameterSets; i++ {
unsigned int(16 sequenceParameterSetLength ;
bit(8*sequenceParameterSetLength sequenceParameterSetNALUnit;
}
unsigned int(8 numOfPictureParameterSets;
for (i = 0; i < numOfPictureParameterSets; i++ {
unsigned int(16 pictureParameterSetLength;
bit(8*pictureParameterSetLength pictureParameterSetNALUnit;
}
if (profile_idc == 100 || profile_idc == 110 ||
profile_idc == 122 || profile_idc == 144
{
bit(6 reserved = '111111'b;
unsigned int(2 chroma_format;
bit(5 reserved = '11111'b;
unsigned int(3 bit_depth_luma_minus8;
bit(5 reserved = '11111'b;
unsigned int(3 bit_depth_chroma_minus8;
unsigned int(8 numOfSequenceParameterSetExt;
for (i = 0; i < numOfSequenceParameterSetExt; i++ {
unsigned int(16 sequenceParameterSetExtLength;
bit(8*sequenceParameterSetExtLength sequenceParameterSetExtNALUnit;
}
}
}
如果是H265，HEVCDecoderConfigurationRecord定义如下：
aligned(8 class HEVCDecoderConfigurationRecord {
unsigned int(8 configurationVersion = 1;
unsigned int(2 general_profile_space;
unsigned int(1 general_tier_flag;
unsigned int(5 general_profile_idc;
unsigned int(32 general_profile_compatibility_flags;
unsigned int(48 general_constraint_indicator_flags;
unsigned int(8 general_level_idc;
bit(4 reserved = ‘1111’b;
unsigned int(12 min_spatial_segmentation_idc;
bit(6 reserved = ‘111111’b;
unsigned int(2 parallelismType;
bit(6 reserved = ‘111111’b;
unsigned int(2 chromaFormat;
bit(5 reserved = ‘11111’b;
unsigned int(3 bitDepthLumaMinus8;
bit(5 reserved = ‘11111’b;
unsigned int(3 bitDepthChromaMinus8;
bit(16 avgFrameRate;
bit(2 constantFrameRate;
bit(3 numTemporalLayers;
bit(1 temporalIdNested;
unsigned int(2 lengthSizeMinusOne;
unsigned int(8 numOfArrays;
for (j=0; j < numOfArrays; j++ {
bit(1 array_completeness;
unsigned int(1 reserved = 0;
unsigned int(6 NAL_unit_type;
unsigned int(16 numNalus;
for (i=0; i< numNalus; i++ {
unsigned int(16 nalUnitLength;
bit(8*nalUnitLength nalUnit;
}
}
}