整体方案：
采集端：摄像头采集（YUV）->编码（YUV转H264）->写封装（Ｈ264转FLV）->RTMP推流
客户端：RTMP拉流->解封装（FLV转H264）->解码（H264转YUV）->YUV显示（SDL2）

#include <stdio.h>#define __STDC_CONSTANT_MACROSextern "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_AACconst char *in_filename    = "demo.flv";		//Input file URLconst char *out_filename_v = "demo.h264";	//Output file URLconst char *out_filename_a = "demo.aac";#endif#if DEMUXER_MP3const char *in_filename    = "demo.flv";		//Input file URLconst char *out_filename_v = "demo.h264";	//Output file URLconst char *out_filename_a = "demo.mp3";#endifav_register_all();//Inputif ((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000001AVBitStreamFilterContext* h264bsfc =  av_bitstream_filter_init("h264_mp4toannexb"); #if DEMUXER_AACADTSContext stADTSContext;unsigned char pAdtsHead[7];
#endifwhile(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_AACaac_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;
}