webrtc自带了Simulcast功能，可以将一个分辨率的流编码成多个分辨率并发送，观看端可以根据带宽去动态的选择某个分辨率，也可以自己选择某个分辨率，据说在webrtc M70版本提供了对外的接口开启Simulcast，并 vp8，vp9，h264三种编码器都支持Simulcast功能，但是在M70版本以下并不支持h264编码器的Simulcast功能，如果在M70版本以下使用Simulcast功能，需要通过修改SDP来开启，话不多说，直接上代码：
- 头文件
//
// sdp_helpers.h
//
// Created by ilong on 2018/10/29.
// Copyright © 2018 ilong. All rights reserved.
//
#ifndef sdp_helpers_h
#define sdp_helpers_h
#include <stdio.h>
#include <string>
#include <vector>
class SdpHelpers {
public:
template<typename T>
static T StringTo(std::string str);
template<typename T>
static std::string ToString(T arg);
// return sdp ，numSpatialLayers 表示开启几路流，一般是2
static std::string EnableSimulcast(const std::string &sdp, const int numSpatialLayers);
private:
SdpHelpers();
~SdpHelpers();
static std::vector<std::string> GetFID(const std::string &sdp);
static std::string GetSsrcTagValue(const std::string &sdp, uint64_t fid, std::string &tag);
static std::string AddSim(std::vector<uint64_t> &spatialLayers);
static std::string AddGroup(uint64_t spatialLayerId, uint64_t spatialLayerIdRtx);
static std::string AddSpatialLayer(std::string &cname, std::string &msid, std::string &mslabel, std::string &label, uint64_t spatialLayerId, uint64_t spatialLayerIdRtx);
static void StrReplace(std::string &baseString, std::string &src, std::string &dst);
static std::string RemoveSsrcLine(std::string &sdp ,uint64_t fid);
static void StringReplace( std::string &strBig, const std::string &strsrc, const std::string &strdst);
};
#endif /* sdp_helpers_h */
- 实现文件
//
// sdp_helpers.cpp
//
// Created by ilong on 2018/10/29.
// Copyright © 2018 ilong. All rights reserved.
//
#include "sdp_helpers.h"
#include <sstream>
#include <regex>
SdpHelpers::SdpHelpers(){
}
SdpHelpers::~SdpHelpers(){
}
template <typename T>
T SdpHelpers::StringTo(std::string str) {
T tmp;
std::stringstream ss;
ss << str;
ss >> tmp;
return tmp;
}
template<typename T>
std::string SdpHelpers::ToString(T arg){
std::stringstream ss;
ss << arg;
return ss.str();
}
std::string SdpHelpers::EnableSimulcast(const std::string &sdp, const int numSpatialLayers){
std::string sdpStr = sdp;
uint64_t baseSsrc = 0, baseSsrcRtx = 0;
std::vector<std::string> results = SdpHelpers::GetFID(sdp);
if (results.size()>2) {
baseSsrc = SdpHelpers::StringTo<uint64_t>(results[1]);
baseSsrcRtx = SdpHelpers::StringTo<uint64_t>(results[2]);
}else{
//LOGW("fid is empty.");
return "";
}
std::string tag = "cname";
std::string cname = SdpHelpers::GetSsrcTagValue(sdp, baseSsrc, tag);
if (cname.length()<=0) {
//LOGW("cname length is 0.");
return "";
}
tag = "msid";
std::string msid = SdpHelpers::GetSsrcTagValue(sdp, baseSsrc, tag);
if (msid.length()<=0) {
//LOGW("msid length is 0.");
return "";
}
tag = "mslabel";
std::string mslabel = SdpHelpers::GetSsrcTagValue(sdp, baseSsrc, tag);
if (mslabel.length()<=0) {
//LOGW("mslabel length is 0.");
return "";
}
tag = "label";
std::string label = SdpHelpers::GetSsrcTagValue(sdp, baseSsrc, tag);
if (label.length()<=0) {
//LOGW("label length is 0.");
return "";
}
sdpStr = SdpHelpers::RemoveSsrcLine(sdpStr, baseSsrc);
sdpStr = SdpHelpers::RemoveSsrcLine(sdpStr, baseSsrcRtx);
std::vector<uint64_t> spatialLayers;
spatialLayers.push_back(baseSsrc);
std::vector<uint64_t> spatialLayersRtx;
spatialLayersRtx.push_back(baseSsrcRtx);
for (int i = 1; i<numSpatialLayers; i++) {
spatialLayers.push_back(baseSsrc+i*1000);
spatialLayersRtx.push_back(baseSsrcRtx+i*1000);
}
std::string result = SdpHelpers::AddSim(spatialLayers);
for (int i = 0; i < spatialLayers.size(); i++) {
result += SdpHelpers::AddGroup(spatialLayers[i], spatialLayersRtx[i]);
}
for (int i = 0; i < spatialLayers.size(); i++) {
result += SdpHelpers::AddSpatialLayer(cname, msid, mslabel, label, spatialLayers[i], spatialLayersRtx[i]);
}
result += "a=x-google-flag:conference\r\n";
SdpHelpers::StrReplace(sdpStr, results[0], result);
return sdpStr;
}
std::vector<std::string> SdpHelpers::GetFID(const std::string &sdp){
std::string pattern{ "a=ssrc-group:FID ([0-9]*) ([0-9]*)\r?\n" }; // id card
std::regex re(pattern);
std::smatch results;
std::vector<std::string> res;
res.clear();
bool ret = std::regex_search(sdp, results, re);
if (ret) {
for (auto item:results) {
res.push_back(item.str());
}
}
return res;
}
std::string SdpHelpers::GetSsrcTagValue(const std::string &sdp, uint64_t fid, std::string &tag){
std::stringstream ss;
ss << "a=ssrc:" << fid <<" "<< tag <<":(.*)\r?\n";
std::regex re(ss.str());
std::smatch results;
bool ret = std::regex_search(sdp, results, re);
if (ret) {
return results[1].str();
}
return "";
}
std::string SdpHelpers::AddSim(std::vector<uint64_t> &spatialLayers){
std::string line{"a=ssrc-group:SIM"};
for (auto item:spatialLayers) {
line+=" "+SdpHelpers::ToString(item);
}
return line+"\r\n";
}
std::string SdpHelpers::AddGroup(uint64_t spatialLayerId, uint64_t spatialLayerIdRtx){
return "a=ssrc-group:FID "+SdpHelpers::ToString(spatialLayerId)+" "+SdpHelpers::ToString(spatialLayerIdRtx)+"\r\n";
}
std::string SdpHelpers::AddSpatialLayer(std::string &cname, std::string &msid, std::string &mslabel, std::string &label, uint64_t spatialLayerId, uint64_t spatialLayerIdRtx){
return "a=ssrc:"+SdpHelpers::ToString(spatialLayerId)+" cname:"+cname+"\r\n"+
"a=ssrc:"+SdpHelpers::ToString(spatialLayerId)+" msid:"+msid+"\r\n"+
"a=ssrc:"+SdpHelpers::ToString(spatialLayerId)+" mslabel:"+mslabel+"\r\n"+
"a=ssrc:"+SdpHelpers::ToString(spatialLayerId)+" label:"+label+"\r\n"+
"a=ssrc:"+SdpHelpers::ToString(spatialLayerIdRtx)+" cname:"+cname+"\r\n"+
"a=ssrc:"+SdpHelpers::ToString(spatialLayerIdRtx)+" msid:"+msid+"\r\n"+
"a=ssrc:"+SdpHelpers::ToString(spatialLayerIdRtx)+" mslabel:"+mslabel+"\r\n"+
"a=ssrc:"+SdpHelpers::ToString(spatialLayerIdRtx)+" label:"+label+"\r\n";
}
void SdpHelpers::StrReplace(std::string &baseString, std::string &src, std::string &dst){
SdpHelpers::StringReplace(baseString, src, dst);
}
void SdpHelpers::StringReplace( std::string &strBig, const std::string &strsrc, const std::string &strdst){
std::string::size_type pos = 0;
std::string::size_type srclen = strsrc.size();
std::string::size_type dstlen = strdst.size();
while( (pos=strBig.find(strsrc, pos)) != std::string::npos ){
strBig.replace( pos, srclen, strdst );
pos += dstlen;
}
}
std::string SdpHelpers::RemoveSsrcLine(std::string &sdp ,uint64_t fid){
std::string retStr = sdp;
std::stringstream ss;
ss << "a=ssrc:" << fid <<".*\r?\n";
std::regex re(ss.str());
std::smatch results;
//多次匹配
while (std::regex_search(retStr, results, re)) {
for (auto item:results) {
SdpHelpers::StringReplace(retStr, item.str(), std::string(""));
}
}
return retStr;
}