WebRTC 如何知道 RTX Stream 的 SSRC

October 8, 2022 by walter

Overview

每个流都有一个配置

struct StreamConfig {
  StreamConfig();
  StreamConfig(const StreamConfig& other);
  ~StreamConfig();

  bool operator==(const StreamConfig& other) const;
  bool operator!=(const StreamConfig& other) const;

  uint32_t local_ssrc = 0;
  uint32_t remote_ssrc = 0;
  uint32_t rtx_ssrc = 0;
  std::string rsid;

  bool remb = false;
  std::vector<RtpExtension> rtp_extensions;

  RtcpMode rtcp_mode = RtcpMode::kReducedSize;

  struct Codec {
    Codec(absl::string_view payload_name,
          int payload_type,
          int rtx_payload_type);

    bool operator==(const Codec& other) const;

    std::string payload_name;
    int payload_type;
    int rtx_payload_type;
  };

  std::vector<Codec> codecs;
};

方法一

通过 SSRC-GROUP

参见

https://source.chromium.org/chromium/chromium/src/+/main:third_party/webrtc/media/engine/webrtc_video_engine.cc;l=281?q=SetSendParameters&ss=chromium%2Fchromium%2Fsrc

static bool ValidateStreamParams(const StreamParams& sp) {
  if (sp.ssrcs.empty()) {
    RTC_LOG(LS_ERROR) << "No SSRCs in stream parameters: " << sp.ToString();
    return false;
  }

  std::vector<uint32_t> primary_ssrcs;
  sp.GetPrimarySsrcs(&primary_ssrcs);
  std::vector<uint32_t> rtx_ssrcs;
  sp.GetFidSsrcs(primary_ssrcs, &rtx_ssrcs);
  for (uint32_t rtx_ssrc : rtx_ssrcs) {
    bool rtx_ssrc_present = false;
    for (uint32_t sp_ssrc : sp.ssrcs) {
      if (sp_ssrc == rtx_ssrc) {
        rtx_ssrc_present = true;
        break;
      }
    }
    if (!rtx_ssrc_present) {
      RTC_LOG(LS_ERROR) << "RTX SSRC '" << rtx_ssrc
                        << "' missing from StreamParams ssrcs: "
                        << sp.ToString();
      return false;
    }
  }
  if (!rtx_ssrcs.empty() && primary_ssrcs.size() != rtx_ssrcs.size()) {
    RTC_LOG(LS_ERROR)
        << "RTX SSRCs exist, but don't cover all SSRCs (unsupported): "
        << sp.ToString();
    return false;
  }

  return true;
}

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