FFmpeg常用指令记录sdp中提取sps/pps信息sps/pps(STAP-A解析)

Author:Peter
Location:FZU
Date: 2022-04-15

：如人饮水，冷暖自知。

ffmpeg编码/推流指令，ffprobe分析H264码流指令。win10系统，git bash终端操作（可使用linux相关指令）。

文章目录

1.ffmpeg利用x264编码YUV文件为H264
2.ffmpeg通过RTP封包推送H264码流
3.ffprobe分析h264文件指令

1.ffmpeg利用x264编码YUV文件为H264

将yuv420压缩成h264 -r:帧率，-g:GOPsize，-bf:B帧数量，-b:v 编码速率，-bufsize:码率控制缓冲区大小

./ffmpeg.exe -s 1920x1080 -i ParkScene_1920x1080.yuv -c:v libx264 -r 25 -g 50 -bf 0 -b:v 2000k -bufsize 2500k ParkScene_in.h264

2.ffmpeg通过RTP封包推送H264码流

注意事项，ffmpeg推送rtp流，IDR帧前不像Live555会采用两个packet封装sps/pps，而是直接一个STAP-A打包方式将sps及pps一同并入一个packet,即一个IDR帧前只含有一个sps&pps信息的packet，如下图抓包显示。

./ffmpeg.exe -re -i ParkScene_in.h264  -an -c copy -f rtp -ssrc 10 rtp://127.0.0.1:9900?pkt_size=1316 > 1.sdp

ffmpeg 推RTP流，IDR帧中sps/pps抓包信息

开头十六进制18的后五位二进制为11000(十进制为24，属于STAP-A封包)，即00 1a为第一个nalu(sps)[67 64… 92 40]的长度，00 05为第二个nalu(pps)[68 eb cc b2 2c]的长度。固接收端解析STAP-A包时，需要将18 00 1a 替换成00 00 00 01，00 05替换成00 00 00 01，记00 00 00 01为一个nalu的起始码。

接收端解析STAP-A(sps/pps)

#include<iostream>
#include<string>
#include<vector>using namespace std;union LENGTH  //可以采用联合体，共用内存空间，length与byte[2]
{uint16_t length;uint8_t  byte[2];
};//0x00 0x1a   0000 0000 0001 1010 = 26
void testSTAP_A()
{char sps_pps[] = { 0x18,0x00,0x1a,0x67,0x64,0x00,0x28,0xac,0xb2,0x00,0xf0,0x04,0x4f,0xcb,0x08,0x00,0x00,0x03,0x00,0x08,0x00,0x00,0x03,0x01,0x90,0x78,0xc1,0x92,0x40,0x00,0x05,0x68,0xeb,0xcc,0xb2,0x2c};int sps_length = 0;int pps_length = 0;//电脑是小端存储，地址低位存放数字低位，这样转过来为0x1a,0x00,0x00,0x00 十进制为26for (int i = 2, j = 0; i >= 1; --i, ++j)memcpy((char*)&sps_length + j, sps_pps + i, 1);cout << "sps_length=" << sps_length << endl;#if 1  //采用联合体计算sps长度，也要考虑到小端存储0x00 0x1a (0x1a在低地址)LENGTH sps;for (int i = 0; i < 2; ++i){sps.byte[i] = sps_pps[2 - i];}cout << sps.length << endl;#endif pps_length = sizeof(sps_pps) - sps_length - 5;//电脑是小端存储，地址低位存放数字低位，这样转过来为00 00 00 01uint32_t start_code = 0x01000000;vector<char> parse_sps_pps(sizeof(sps_pps) + 2 * 4 - 5);memcpy(parse_sps_pps.data(), &start_code, 4);memcpy(parse_sps_pps.data() + 4, sps_pps + 3, sps_length);memcpy(parse_sps_pps.data() + 4 + sps_length, &start_code, 4);memcpy(parse_sps_pps.data() + 8 + sps_length, sps_pps + 5 + sps_length, pps_length);
}int main()
{testSTAP_A();return 0;
}

指令生成的sdp信息:

SDP:
v=0
o=- 0 0 IN IP4 127.0.0.1
s=No Name
c=IN IP4 127.0.0.1
t=0 0
a=tool:libavformat 58.76.100
m=video 9900 RTP/AVP 96
a=rtpmap:96 H264/90000
a=fmtp:96 packetization-mode=1; sprop-parameter-sets=Z2QAKKyyAPAET8sIAAADAAgAAAMBkHjBkkA=,aOvMsiw=; profile-level-id=640028

提取sdp中的sps/pps信息（base64编码，逗号是分割sps,pps）

sprop-parameter-sets=Z2QAKKyyAPAET8sIAAADAAgAAAMBkHjBkkA=,aOvMsiw=

其中sps信息: Z2QAKKyyAPAET8sIAAADAAgAAAMBkHjBkkA=
pps信息: aOvMsiw=

C/C++代码提取sps/pps

#include <iostream>
#include <fstream>
#include <string>using namespace std;int main()
{ifstream inf("..\\ffmpeg_bin\\1.sdp");string oneline;string sps_sdp;string pps_sdp;string sps_pps_sdp;int sps_start,pps_start,pps_end;while (true){getline(inf, oneline);if (inf.eof() == true)break;cout << oneline << "\n";if ((sps_start = oneline.find("-sets=")) >0 && (pps_end = oneline.find("; profile")) >0 ){sps_start += 6;sps_pps_sdp.assign(oneline.data() + sps_start, oneline.data() + pps_end);}}if ((pps_start = sps_pps_sdp.find(",")) > 0){sps_sdp.assign(sps_pps_sdp.data(), sps_pps_sdp.data() + pps_start);pps_sdp.assign(sps_pps_sdp.data() + pps_start + 1, sps_pps_sdp.data() + sps_pps_sdp.size());cout << "sps:"<<sps_sdp << "\t" <<"pps:"<< pps_sdp << endl;}return 0;
}//----------------运行结果如下：----------------------
SDP:
v=0
o=- 0 0 IN IP4 127.0.0.1
s=No Name
c=IN IP4 127.0.0.1
t=0 0
a=tool:libavformat 58.76.100
m=video 9900 RTP/AVP 96
a=rtpmap:96 H264/90000
a=fmtp:96 packetization-mode=1; sprop-parameter-sets=Z2QAKKyyAPAET8sIAAADAAgAAAMBkHjBkkA=,aOvMsiw=; profile-level-id=640028sps:Z2QAKKyyAPAET8sIAAADAAgAAAMBkHjBkkA=    pps:aOvMsiw=

3.ffprobe分析h264文件指令

查看h264码流I/B/P帧分布

./ffprobe.exe -v error -show_frames ParkScene_in.h264 | grep "pict_type"

统计h264码流总帧数

./ffprobe.exe -v error -count_frames -select_streams v:0  -show_entries stream=nb_read_frames -of default=nokey=1:noprint_wrappers=1 ParkScene_in.h264

查看h264码流信息

./ffprobe.exe -v error -show_streams ParkScene_in.h264

has_b_frames=0意味着264码流中无B帧。