javascript - WebRTC - 如何区分通过同一连接发送的两个 MediaStreamTracks？

Question

我想使用 WebRTC 将两个视频流从 Peer1 发送到 Peer2:让我们以前置和后置摄像头为例。

从概念上讲，Peer2 如何知道哪个流来自哪个摄像头？

MediaStream documentation提到所有 MediaStream 和 MediaStreamTrack 字段都是只读的，所以我不能直接向它们附加任何信息。我无法通过信令 channel 发送像 {"stream1 id": "camera", "stream2 id": "screenshare"} 这样的字典，因为 Peer2 将为每个流和轨道生成自己的 ID。

Answer 1

https://datatracker.ietf.org/doc/html/draft-ietf-mmusic-msid-11

In the RTP specification, media streams are identified using the SSRC
field.  Streams are grouped into RTP Sessions, and also carry a
CNAME.  Neither CNAME nor RTP session correspond to a MediaStream.
Therefore, the association of an RTP media stream to MediaStreams
need to be explicitly signaled.

WebRTC defines a mapping (documented in [I-D.ietf-rtcweb-jsep]) where
one SDP media description is used to describe each MediaStreamTrack,
and the BUNDLE mechanism [I-D.ietf-mmusic-sdp-bundle-negotiation] is
used to group MediaStreamTracks into RTP sessions.  Therefore, the
need is to specify the ID of a MediaStreamTrack and its associated
MediaStream for each media description, which can be accomplished
with a media-level SDP attribute.

This document defines a new SDP [RFC4566] media-level "msid"
attribute.  This new attribute allows endpoints to associate RTP
media streams that are described in different media descriptions with
the same MediaStreams as defined in [W3C.WD-webrtc-20150210]., and to
carry an identifier for each MediaStreamTrack in its "appdata" field.

因此，在浏览器支持自定义 msid 之前，这似乎无法完成。