• RtpPayloadParams 看起来是rtp 载荷的属性的类 ，
• 每个payload可能映射到某个帧 ？
• 可能payload 映射到多个frameid ？

Maps buffer IDs to the frame-ID stored in them.

• • int64 类型的bufferid 映射到一个 frameid 类型

  // TODO(eladalon): When additional codecs are supported,
  // set kMaxCodecBuffersCount to the max() of these codecs' buffer count.
  static constexpr size_t kMaxCodecBuffersCount =
      CodecSpecificInfoVP8::kBuffersCount;

  // Maps buffer IDs to the frame-ID stored in them.
  std