WEBRTC視訊編解碼支援H264 VP8 VP9 但是預設是VP8 ，根據SDP描述協商

WEBRTC H264編碼採用OPENH264 解碼採用FFMPEG

一 讓WEBRTC支援H264編碼

1. 修改配置支援H264編碼

 webrtc/build/common.gypi  rtc_use_h264=1(只要有都設為1)，這樣OPENH264就會生成

 然後需要重新編譯 python webrtc/build/gyp_webrtc ninja -C out/Debug

2 修改SDP生成次序

webrtcvideoengine2.cc DefaultVideoCodecList 可以修改SDP中 視訊編碼的次序把

放在最前面，讓SDP支援H264

  if (CodecIsInternallySupported(kH264CodecName)) {
    VideoCodec codec = MakeVideoCodecWithDefaultFeedbackParams(
        kDefaultH264PlType, kH264CodecName);
    // TODO(hta): Move all parameter generation for SDP into the codec
    // implementation, for all codecs and parameters.
    // TODO(hta): Move selection of profile-level-id to H.264 codec
    // implementation.
    // TODO(hta): Set FMTP parameters for all codecs of type H264.
    codec.SetParam(kH264FmtpProfileLevelId,
                   kH264ProfileLevelConstrainedBaseline);
    codec.SetParam(kH264FmtpLevelAsymmetryAllowed, "1");
    codec.SetParam(kH264FmtpPacketizationMode, "1");
    codecs.push_back(codec);
    codecs.push_back(
        VideoCodec::CreateRtxCodec(kDefaultRtxH264PlType, kDefaultH264PlType));
  }
 

二 讓WEBRTC支援H264解碼
thirdpart 下有ffmpeg原始碼，不用下載ffmpeg編譯
1.修改gyp配置 支援ffmpeg編譯<webrtc/build/common.gypi rtc_initialize_ffmpeg=1
2.預設ffmpeg 不會把h264.c等檔案編譯進ffmpeg 就會導致 H264DecoderImpl::InitDecode 呼叫 avcodec_find_decoder 失敗，
找不到解碼器需要修改 ffmpeg_generated.gypi 預設只支援chrome chromeOS中編譯H264，找到h264.c
然後 在LINUX X64 中去掉chrome

 ['(OS == "linux" and target_arch == "arm" and arm_neon == 1 and ffmpeg_branding == "Chrome") or (OS == "linux" and target_arch == "arm" and arm_neon == 1 and ffmpeg_branding == "ChromeOS") or (OS == "linux" and target_arch == "arm" and ffmpeg_branding == "Chrome") or (OS == "linux" and target_arch == "arm" and ffmpeg_branding == "ChromeOS") or (OS == "linux" and target_arch == "arm64" and ffmpeg_branding == "Chrome") or (OS == "linux" and target_arch == "arm64" and ffmpeg_branding == "ChromeOS") or (OS == "linux" and target_arch == "ia32" and ffmpeg_branding == "Chrome") or (OS == "linux" and target_arch == "ia32" and ffmpeg_branding == "ChromeOS") or (OS == "linux" and target_arch == "mipsel" and ffmpeg_branding == "Chrome") or (OS == "linux" and target_arch == "mipsel" and ffmpeg_branding == "ChromeOS") or (OS == "linux" and target_arch == "x64" and ffmpeg_branding == "Chrome") or(OS == "linux" and target_arch == "x64")or (OS == "mac" and target_arch == "x64" and ffmpeg_branding == "Chrome") or (OS == "win" and target_arch == "ia32" and ffmpeg_branding == "Chrome") or (OS == "win" and target_arch == "x64" and ffmpeg_branding == "Chrome")', {

再找到

          'libavcodec/x86/h264_qpel.c',
          'libavcodec/x86/h264chroma_init.c',
          'libavcodec/x86/h264dsp_init.c',

對應得

['(OS == "linux" and target_arch == "ia32" and ffmpeg_branding == "Chrome") or (OS == "linux" and target_arch == "ia32" and ffmpeg_branding == "ChromeOS") or (OS == "linux" and target_arch == "x64" and ffmpeg_branding == "Chrome") or <span style="color:#ff0000;">(OS == "linux" and target_arch == "x64")</span> or (OS == "mac" and target_arch == "x64" and ffmpeg_branding == "Chrome") or (OS == "win" and target_arch == "ia32" and ffmpeg_branding == "Chrome") or (OS == "win" and target_arch == "x64" and ffmpeg_branding == "Chrome")', {

在LINUX X64 中去掉chrome

3.重新生成ninja python webrtc/build/gyp_webrtc ninja -C out/Debug

可在video_send_stream.cc 函式，中除錯 encoded_image._buffer 看碼流或寫入檔案

int32_t VideoSendStream::Encoded(const EncodedImage& encoded_image,
                                 const CodecSpecificInfo* codec_specific_info,
                                 const RTPFragmentationHeader* fragmentation) 

</pre><pre class="cpp" name="code" snippet_file_name="blog_20160630_8_8873287" code_snippet_id="1736351">