windows webrtc 支持h264编码

下载完webrtc代码之后

1、打开src目录下的.gn文件
2、在default_args里面添加
   rtc_use_h264 = true
   ffmpeg_branding = "Chrome"
   

如下：   
default_args = {
  # Webrtc does not support component builds because we are not using the
  # template "component" but we rely directly on "rtc_static_library" and
  # "rtc_shared_library". This means that we cannot use the chromium default
  # value for this argument.
  # This also means that the user can override this value using --args or
  # the args.gn file but this setting will be ignored because we don't support
  # component builds.
  is_component_build = false
  rtc_use_h264 = true
  ffmpeg_branding = "Chrome"
  }

3、重新运行gn   
例如：
gn gen out/Default --ide="vs2015"