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原文： https://blog.csdn.net/hiwubihe/article/details/82346759
[本系列相关文章]
- H264和音频流打包成PS流 (MPEG2-PS)
- PS流解复用成H264和音频流(ES提取)
- H264和音频流打包成TS流 (MPEG2-TS)
- TS流解复用成H264和音频流(ES提取)
- FLV文件格式基础
- 解复用FLV文件(基于FFMPEG解析FLV(h264+aac))
- 解复用FLV文件(不用FFMPEG,C++实现)
本篇介绍基于FFMPEG解析FLV文件，FLV由H264视频和AAC音频组成。FFMPEG 解复用出的音视频AVPacket，直接写入文件播放不了。FLV格式最常用的封装组合就是H264+AAC,FFMPEG解复用的结果AVPacket只包含实际的压缩音视频数据，不包括解码必须的信息，H264的SPS+PPS,AAC的视频头ADTS等。这就需要从FLV中提取SPS+PPS信息，和ADTS信息加到音视频帧前面。
1.FLV文件AVCDecoderConfigurationRecord
封装FLV，一般第一个VideoTag就是AVCDecoderConfigurationRecord结构，该结构就是H264的SPS+PPS信息
AVCDecoderConfigurationRecord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;
}
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;
}
}
2.FLV文件AudioSpecificConfig
封装FLV，一般第一个AudioTag就是AudioSpecificConfig结构，该结构就是AAC封装头ADTS需要的信息，采样率，通道数，样本深度等信息。
AudioSpecificConfig在所有封装AAC的文件结构中都有，如FLV/MP4。 AudioSpecificConfig结构比较复杂。一般结构就是2个字节。在MP4文件中一般叫AES,一般结构如下表
| 总体结构 | 5 bits: object type
if (object type == 31)
6 bits + 32: object type
4 bits: frequency index
if (frequency index == 15)
24 bits: frequency
4 bits: channel configuration
var bits: AOT Specific Config |
| ObjectType |
|
| 采样率索引 |
|
| Channels |
|
解析AES代码
typedef struct
{
int write_adts;
int objecttype;
int sample_rate_index;
int channel_conf;
}ADTSContext;
int aac_decode_extradata(ADTSContext *adts, unsigned char *pbuf, int bufsize)
{
int aot, aotext, samfreindex;
int i, channelconfig;
unsigned char *p = pbuf;
if (!adts || !pbuf || bufsize<2)
{
return -1;
}
aot = (p[0]>>3)&0x1f;
if (aot == 31)
{
aotext = (p[0]<<3 | (p[1]>>5)) & 0x3f;
aot = 32 + aotext;
samfreindex = (p[1]>>1) & 0x0f;
if (samfreindex == 0x0f)
{
channelconfig = ((p[4]<<3) | (p[5]>>5)) & 0x0f;
}
else
{
channelconfig = ((p[1]<<3)|(p[2]>>5)) & 0x0f;
}
}
else
{
samfreindex = ((p[0]<<1)|p[1]>>7) & 0x0f;
if (samfreindex == 0x0f)
{
channelconfig = (p[4]>>3) & 0x0f;
}
else
{
channelconfig = (p[1]>>3) & 0x0f;
}
}
#ifdef AOT_PROFILE_CTRL
if (aot < 2) aot = 2;
#endif
adts->objecttype = aot-1;
adts->sample_rate_index = samfreindex;
adts->channel_conf = channelconfig;
adts->write_adts = 1;
return 0;
} 构造AES代码
//获取音频AES值
bool GetDecoderSpecificInfo(AdtsHeadInfo stAdtsHeadInfo,unsigned char*pBuffer,unsigned long &lSizeOfDecoderSpecificInfo)
{
lSizeOfDecoderSpecificInfo = 2;
memset(pBuffer,0,lSizeOfDecoderSpecificInfo);
bits_buffer_t bw;
bits_initwrite (&bw, lSizeOfDecoderSpecificInfo, pBuffer);
bits_write (&bw, 5, stAdtsHeadInfo.iProfile);
bits_write (&bw, 4, stAdtsHeadInfo.iSampleRateIndex);
bits_write (&bw, 4, stAdtsHeadInfo.iChans);
memcpy(pBuffer, bw.p_data, lSizeOfDecoderSpecificInfo);
return true;
}3.FFMPEG处理原理
在av_read_frame函数调用中，如果读到AVCDecoderConfigurationRecord或者AudioSpecificConfig结构时，会把信息保存在每个stream的streams[index]->codec->extradata扩展数据中。处理H264数据时，提供一个叫 “h264_mp4toannexb”比特流过滤器，在av_read_frame读取到正常数据包时，需要调用比特流过滤器处理每个数据包，其实就是判断是否是I帧，是I帧的话，解析AVCDecoderConfigurationRecord结构成SPS+PPS,然后把SPS+PPS保存加到I帧前面。可以参考FFMPEG源码，版本3.2.4.r86064。下面代码就是循环处理接受到的数据，添加SPS/PPS。
static int h264_mp4toannexb_filter(AVBSFContext *ctx, AVPacket *out)
{
H264BSFContext *s = ctx->priv_data;
AVPacket *in;
uint8_t unit_type;
int32_t nal_size;
uint32_t cumul_size = 0;
const uint8_t *buf;
const uint8_t *buf_end;
int buf_size;
int ret = 0, i;
//读取的数据包复制到in
ret = ff_bsf_get_packet(ctx, &in);
if (ret < 0)
return ret;
/* nothing to filter */
//不需要过滤 直接赋值
if (!s->extradata_parsed)
{
av_packet_move_ref(out, in);
av_packet_free(&in);
return 0;
}
buf = in->data;
buf_size = in->size;
buf_end = in->data + in->size;
do
{
ret= AVERROR(EINVAL);
//长度错误
if (buf + s->length_size > buf_end)
goto fail;
//获取NALU长度
for (nal_size = 0, i = 0; i<s->length_size; i++)
nal_size = (nal_size << 8) | buf[i];
//向后移动s->length_size
buf += s->length_size;
//NALU type
unit_type = *buf & 0x1f;
//长度出错
if (nal_size > buf_end - buf || nal_size < 0)
goto fail;
//SPS数据 新的IDR标志 SPS直接拷贝加到缓存中
if (unit_type == 7)
s->idr_sps_seen = s->new_idr = 1;
//PPS数据 新的IDR标志
else if (unit_type == 8)
{
s->idr_pps_seen = s->new_idr = 1;
/* if SPS has not been seen yet, prepend the AVCC one to PPS */
//当前是收到pps包 前面却没有SPS包，需要从扩展数据中把SPS加上
//如果有sps 直接走到 一般数据拷贝else
if (!s->idr_sps_seen)
{
if (s->sps_offset == -1)
av_log(ctx, AV_LOG_WARNING, "SPS not present in the stream, nor in AVCC, stream may be unreadable\n");
else
{
//把sps和pps 都拷贝到数据缓存中
if ((ret = alloc_and_copy(out,
ctx->par_out->extradata + s->sps_offset,
s->pps_offset != -1 ? s->pps_offset : ctx->par_out->extradata_size - s->sps_offset,
buf, nal_size)) < 0)
goto fail;
s->idr_sps_seen = 1;
goto next_nal;
}
}
}
/* if this is a new IDR picture following an IDR picture, reset the idr flag.
* Just check first_mb_in_slice to be 0 as this is the simplest solution.
* This could be checking idr_pic_id instead, but would complexify the parsing. */
if (!s->new_idr && unit_type == 5 && (buf[1] & 0x80))
s->new_idr = 1;
/* prepend only to the first type 5 NAL unit of an IDR picture, if no sps/pps are already present */
//新的IDR
if (s->new_idr && unit_type == 5 && !s->idr_sps_seen && !s->idr_pps_seen)
{
if ((ret=alloc_and_copy(out,
ctx->par_out->extradata, ctx->par_out->extradata_size,
buf, nal_size)) < 0)
goto fail;
s->new_idr = 0;
/* if only SPS has been seen, also insert PPS */
}
else if (s->new_idr && unit_type == 5 && s->idr_sps_seen && !s->idr_pps_seen)
{
if (s->pps_offset == -1)
{
av_log(ctx, AV_LOG_WARNING, "PPS not present in the stream, nor in AVCC, stream may be unreadable\n");
if ((ret = alloc_and_copy(out, NULL, 0, buf, nal_size)) < 0)
goto fail;
}
else if ((ret = alloc_and_copy(out,
ctx->par_out->extradata + s->pps_offset, ctx->par_out->extradata_size - s->pps_offset,
buf, nal_size)) < 0)
goto fail;
}
else
{
if ((ret=alloc_and_copy(out, NULL, 0, buf, nal_size)) < 0)
goto fail;
if (!s->new_idr && unit_type == 1)
{
s->new_idr = 1;
s->idr_sps_seen = 0;
s->idr_pps_seen = 0;
}
}
next_nal:
buf += nal_size;
cumul_size += nal_size + s->length_size;
}
while (cumul_size < buf_size);
ret = av_packet_copy_props(out, in);
if (ret < 0)
goto fail;
fail:
if (ret < 0)
av_packet_unref(out);
av_packet_free(&in);
return ret;
}4.解析AudioSpecificConfig
AAC也会把AudioSpecificConfig保存到streams[index]->codec->extradata扩展数据中，但是FFMPEG 没有提供加ADTS的比特流过滤器，需要自己解析AudioSpecificConfig，然后添加到AAC帧前面。
//解析AudioSpecificConfig
int aac_decode_extradata(ADTSContext *adts, unsigned char *pbuf, int bufsize)
{
int aot, aotext, samfreindex;
int i, channelconfig;
unsigned char *p = pbuf;
if (!adts || !pbuf || bufsize<2)
{
return -1;
}
aot = (p[0]>>3)&0x1f;
if (aot == 31)
{
aotext = (p[0]<<3 | (p[1]>>5)) & 0x3f;
aot = 32 + aotext;
samfreindex = (p[1]>>1) & 0x0f;
if (samfreindex == 0x0f)
{
channelconfig = ((p[4]<<3) | (p[5]>>5)) & 0x0f;
}
else
{
channelconfig = ((p[1]<<3)|(p[2]>>5)) & 0x0f;
}
}
else
{
samfreindex = ((p[0]<<1)|p[1]>>7) & 0x0f;
if (samfreindex == 0x0f)
{
channelconfig = (p[4]>>3) & 0x0f;
}
else
{
channelconfig = (p[1]>>3) & 0x0f;
}
}
#ifdef AOT_PROFILE_CTRL
if (aot < 2) aot = 2;
#endif
adts->objecttype = aot-1;
adts->sample_rate_index = samfreindex;
adts->channel_conf = channelconfig;
adts->write_adts = 1;
return 0;
} 5.DEMO程序
程序运用ffmpeg把h264+aac封装的FLV，解复用成两个文件，h264文件和AAC文件。
/*******************************************************************************
Copyright (c) wubihe Tech. Co., Ltd. All rights reserved.
--------------------------------------------------------------------------------
Date Created: 2014-10-25
Author: wubihe QQ:1269122125 Email:[email protected]
Description: 解复用flv保存成h264文件和aac文件
--------------------------------------------------------------------------------
Modification History
DATE AUTHOR DESCRIPTION
--------------------------------------------------------------------------------
********************************************************************************/
#include <stdio.h>
#define __STDC_CONSTANT_MACROS
extern "C"
{
#include "libavformat/avformat.h"
};
//封装格式MKV/MP4/FLV中如果有AAC的情况，首先这些封装格式中包含AudioSpecificConfig，
//保存在音频流的AVCodecContext->extradata 里面，需要解析然后封装ADTS即可
#define DEMUXER_AAC 1
#define DEMUXER_MP3 0
#define ADTS_HEADER_SIZE (7)
//FLV封装音视频 AAC封装在第一个AAC TAG会封装一个AudioSpecificConfig结构
//AudioSpecificConfig解析结果保存在该结构体中
typedef struct
{
int write_adts;
int objecttype;
int sample_rate_index;
int channel_conf;
}ADTSContext;
//解析AudioSpecificConfig
int aac_decode_extradata(ADTSContext *adts, unsigned char *pbuf, int bufsize)
{
int aot, aotext, samfreindex;
int i, channelconfig;
unsigned char *p = pbuf;
if (!adts || !pbuf || bufsize<2)
{
return -1;
}
aot = (p[0]>>3)&0x1f;
if (aot == 31)
{
aotext = (p[0]<<3 | (p[1]>>5)) & 0x3f;
aot = 32 + aotext;
samfreindex = (p[1]>>1) & 0x0f;
if (samfreindex == 0x0f)
{
channelconfig = ((p[4]<<3) | (p[5]>>5)) & 0x0f;
}
else
{
channelconfig = ((p[1]<<3)|(p[2]>>5)) & 0x0f;
}
}
else
{
samfreindex = ((p[0]<<1)|p[1]>>7) & 0x0f;
if (samfreindex == 0x0f)
{
channelconfig = (p[4]>>3) & 0x0f;
}
else
{
channelconfig = (p[1]>>3) & 0x0f;
}
}
#ifdef AOT_PROFILE_CTRL
if (aot < 2) aot = 2;
#endif
adts->objecttype = aot-1;
adts->sample_rate_index = samfreindex;
adts->channel_conf = channelconfig;
adts->write_adts = 1;
return 0;
}
//添加ADTS头
int aac_set_adts_head(ADTSContext *acfg, unsigned char *buf, int size)
{
unsigned char byte;
if (size < ADTS_HEADER_SIZE)
{
return -1;
}
buf[0] = 0xff;
buf[1] = 0xf1;
byte = 0;
byte |= (acfg->objecttype & 0x03) << 6;
byte |= (acfg->sample_rate_index & 0x0f) << 2;
byte |= (acfg->channel_conf & 0x07) >> 2;
buf[2] = byte;
byte = 0;
byte |= (acfg->channel_conf & 0x07) << 6;
byte |= (ADTS_HEADER_SIZE + size) >> 11;
buf[3] = byte;
byte = 0;
byte |= (ADTS_HEADER_SIZE + size) >> 3;
buf[4] = byte;
byte = 0;
byte |= ((ADTS_HEADER_SIZE + size) & 0x7) << 5;
byte |= (0x7ff >> 6) & 0x1f;
buf[5] = byte;
byte = 0;
byte |= (0x7ff & 0x3f) << 2;
buf[6] = byte;
return 0;
}
int main(int argc, char* argv[])
{
AVFormatContext *ifmt_ctx = NULL;
AVPacket pkt;
int ret, i;
int videoindex=-1,audioindex=-1;
#if DEMUXER_AAC
const char *in_filename = "titanic.flv"; //Input file URL
const char *out_filename_v = "titanic.h264"; //Output file URL
const char *out_filename_a = "titanic.aac";
#endif
#if DEMUXER_MP3
const char *in_filename = "titanic.flv"; //Input file URL
const char *out_filename_v = "titanic.h264"; //Output file URL
const char *out_filename_a = "titanic.mp3";
#endif
av_register_all();
//Input
if ((ret = avformat_open_input(&ifmt_ctx, in_filename, 0, 0)) < 0)
{
printf( "Could not open input file.");
return -1;
}
if ((ret = avformat_find_stream_info(ifmt_ctx, 0)) < 0)
{
printf( "Failed to retrieve input stream information");
return -1;
}
videoindex=-1;
for(i=0; i<ifmt_ctx->nb_streams; i++)
{
if(ifmt_ctx->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO)
{
videoindex=i;
}else if(ifmt_ctx->streams[i]->codec->codec_type==AVMEDIA_TYPE_AUDIO)
{
audioindex=i;
}
}
FILE *fp_audio=fopen(out_filename_a,"wb+");
FILE *fp_video=fopen(out_filename_v,"wb+");
//FLV/MP4/MKV等结构中，h264需要h264_mp4toannexb处理。添加SPS/PPS等信息。FLV封装时，可以把
//多个NALU放在一个VIDEO TAG中,结构为4B NALU长度+NALU1+4B NALU长度+NALU2+...,需要做的处理把4B
//长度换成00000001或者000001
AVBitStreamFilterContext* h264bsfc = av_bitstream_filter_init("h264_mp4toannexb");
#if DEMUXER_AAC
ADTSContext stADTSContext;
unsigned char pAdtsHead[7];
#endif
while(av_read_frame(ifmt_ctx, &pkt)>=0)
{
if(pkt.stream_index==videoindex)
{
av_bitstream_filter_filter(h264bsfc, ifmt_ctx->streams[videoindex]->codec, NULL, &pkt.data, &pkt.size, pkt.data, pkt.size, 0);
printf("Write Video Packet. size:%d\tpts:%lld\n",pkt.size,pkt.pts);
fwrite(pkt.data,1,pkt.size,fp_video);
}
else if(pkt.stream_index==audioindex)
{
//AAC在封装结构MKV/FLV/MP4结构中，需要手动添加ADTS
#if DEMUXER_AAC
aac_decode_extradata(&stADTSContext, ifmt_ctx->streams[audioindex]->codec->extradata, ifmt_ctx->streams[audioindex]->codec->extradata_size);
aac_set_adts_head(&stADTSContext, pAdtsHead, pkt.size);
fwrite(pAdtsHead, 1, 7, fp_audio);
#endif
//一般结构如MP3直接写文件即可
printf("Write Audio Packet. size:%d\tpts:%lld\n",pkt.size,pkt.pts);
fwrite(pkt.data,1,pkt.size,fp_audio);
}
av_free_packet(&pkt);
}
av_bitstream_filter_close(h264bsfc);
fclose(fp_video);
fclose(fp_audio);
avformat_close_input(&ifmt_ctx);
if (ret < 0 && ret != AVERROR_EOF)
{
printf( "Error occurred.\n");
return -1;
}
return 0;
}
6.运行结果
生成titanic.h264和titanic.aac两个文件，用ffplay.exe可以验证播放。
编译环境： Win7_64bit+VS2008
DEMO下载地址:https://download.csdn.net/download/hiwubihe/10643142