WebRtc(M105)视频编码器选择代码分析

本文WebRtc 视频编码器选择代码分析，基于M105版本。

编码参数设置到WebRtcEngine模块里 WebRtcVideoChannel，会调用到这里：

bool WebRtcVideoChannel::GetChangedSendParameters(
    const VideoSendParameters& params,
    ChangedSendParameters* changed_params) const {
  if (!ValidateCodecFormats(params.codecs) ||
      !ValidateRtpExtensions(params.extensions, send_rtp_extensions_)) {
    return false;
  }
 
  std::vector<VideoCodecSettings> negotiated_codecs =
      SelectSendVideoCodecs(MapCodecs(params.codecs));

SelectSendVideoCodecs 函数：

std::vector<WebRtcVideoChannel::VideoCodecSettings>
WebRtcVideoChannel::SelectSendVideoCodecs(
    const std::vector<VideoCodecSettings>& remote_mapped_codecs) const {
  std::vector<webrtc::SdpVideoFormat> sdp_formats =
      encoder_factory_ ? encoder_factory_->GetImplementations()
                       : std::vector<webrtc::SdpVideoFormat>();

会调用encoder_factory_->GetImplementations() 函数，

std::vector<SdpVideoFormat>
NebulaVideoEncoderFactory::GetSupportedFormats() const {
  NSLog(@"yinyinyin NebulaVideoEncoderFactory::GetSupportedFormats ");
  std::vector<SdpVideoFormat> supported_formats;
  for (RTC_OBJC_TYPE(RTCVideoCodecInfo) * supportedCodec in
       [encoder_factory_ supportedCodecs]) {
    SdpVideoFormat format = [supportedCodec nativeSdpVideoFormat];
    supported_formats.push_back(format);
  }
 
  for (const webrtc::SdpVideoFormat &format : SupportedX264Codecs())
    supported_formats.push_back(format);
 
  return supported_formats;
}

最终调用到 RTCDefaultVideoEncoderFactory的 supportedCodecs,里面是所有支持的视频编码能力集合，这里添加需H265支持。

+ (NSArray<RTC_OBJC_TYPE(RTCVideoCodecInfo) *> *)supportedCodecs {
  NSDictionary<NSString *, NSString *> *constrainedHighParams = @{
    @"profile-level-id" : kRTCMaxSupportedH264ProfileLevelConstrainedHigh,
    @"level-asymmetry-allowed" : @"1",
    @"packetization-mode" : @"1",
  };
  RTC_OBJC_TYPE(RTCVideoCodecInfo) *constrainedHighInfo =
      [[RTC_OBJC_TYPE(RTCVideoCodecInfo) alloc] initWithName:kRTCVideoCodecH264Name
                                                  parameters:constrainedHighParams];
 
  NSDictionary<NSString *, NSString *> *constrainedBaselineParams = @{
    @"profile-level-id" : kRTCMaxSupportedH264ProfileLevelConstrainedBaseline,
    @"level-asymmetry-allowed" : @"1",
    @"packetization-mode" : @"1",
  };
  RTC_OBJC_TYPE(RTCVideoCodecInfo) *constrainedBaselineInfo =
      [[RTC_OBJC_TYPE(RTCVideoCodecInfo) alloc] initWithName:kRTCVideoCodecH264Name
                                                  parameters:constrainedBaselineParams];
 
#if defined(WEBRTC_MAC)
  NSDictionary<NSString *, NSString *> *constrainedMainParams = @{
    @"profile-level-id" : kRTCSupportedH264ProfileLevelConstrainedMain,
    @"level-asymmetry-allowed" : @"1",
    @"packetization-mode" : @"1",
  };
  RTC_OBJC_TYPE(RTCVideoCodecInfo) *constrainedMainInfo =
      [[RTC_OBJC_TYPE(RTCVideoCodecInfo) alloc] initWithName:kRTCVideoCodecH264Name
                                                  parameters:constrainedMainParams];
#endif
 
  RTC_OBJC_TYPE(RTCVideoCodecInfo) *vp8Info =
      [[RTC_OBJC_TYPE(RTCVideoCodecInfo) alloc] initWithName:kRTCVideoCodecVp8Name];
 
  NSMutableArray<RTC_OBJC_TYPE(RTCVideoCodecInfo) *> *result = [@[
    constrainedHighInfo,
    constrainedBaselineInfo,
#if defined(WEBRTC_MAC)
    constrainedMainInfo,
#endif
    vp8Info,
  ] mutableCopy];
 
  if ([RTC_OBJC_TYPE(RTCVideoEncoderVP9) isSupported]) {
    [result
        addObject:[[RTC_OBJC_TYPE(RTCVideoCodecInfo) alloc] initWithName:kRTCVideoCodecVp9Name]];
  }
 
#if defined(RTC_USE_LIBAOM_AV1_ENCODER)
  [result addObject:[[RTC_OBJC_TYPE(RTCVideoCodecInfo) alloc] initWithName:kRTCVideoCodecAv1Name]];
#endif
    
#ifdef WEBRTC_USE_H265
  RTC_OBJC_TYPE(RTCVideoCodecInfo) *h265Info = [[RTC_OBJC_TYPE(RTCVideoCodecInfo) alloc] initWithName:kRTCVideoCodecH265Name];
  [result addObject:h265Info];
#endif
  return result;
}