ljm_5x/modules/RTC/ortc

ORTC shim for Edge

The modules/RTC/ortc folder contains a RTCPeerConnection shim for Edge based on ORTC among with other shims (such as RTCSessionDescription) and some utilities/helpers to deal with both, SDP and ORTC objects.

Files in ortc folder

RTCPeerConnection.js

Exports a RTCPeerConnection shim. The interface is based on the W3C specification of 2015, which matches (mostly) the current implementation of Chrome.

It also implements Plan-B for multi-stream.

Limitations

• BUNDLE is assumed (single transport for all the local and remote media streams).
• rtcp-mux is assumed (not a real problem nowadays).
• Calling createOffer() is not implemented, so P2P mode is not supported (RTCBrowserType.isP2PSupported() returns false).
• Calling setRemoteDescription() with a SDP answer with mangled SSRC values is currently unsupported (those new SSRC values will not be used for sending media).
• If the app calls createAnswer(), mangles SSRC values, and applies by calling setLocalDescription(), those new SSRC values are currently ignored.
• Simulcast not supported (currently Edge supports maxFramerate per encoding but it does not support maxBitrate, resolutionScale or framerateScale, so it’s not worth it).
• RTCDataChannel not supported (Edge does not implement it).
• addIceCandidate() not supported (it’s never called anyway, at least in non P2P mode). Edge does not support Trickle-ICE which means that, after reading all the remote ICE candidates from the remote SDP and applying them, an “empty” candidate must be immediately applied (otherwise the RTCIceTransport never enters the “completed” state) and, after that, new remote candidates cannot be added.

RTCSessionDescription.js

Exports a RTCSessionDescription shim.

The interface is the same as in the WebRTC specification (although internally it also handles a Object representation of the SDP generated by the sdp-transform library).

errors.js

Exports some Error based classes needed in WebRTC (such as InvalidStateError).

utils.js

Some utilities related to SDP and ORTC.

Issues

ICE error: Wrong MESSAGE-INTEGRITY

Randomly, ICE Binding Requests from Edge are replied with WRONG MESSAGE-INTEGRITY error by the bridge. It seems that Edge, sometimes, adds a extra byte in the USERNAME attribute producing such an issue.

• GitHub issue: https://github.com/jitsi/lib-jitsi-meet/issues/498
• Edge issue: https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/12332457/

Wrong VP8 video from Edge to Chrome if ENABLE_VP8_PICID_REWRITING=True

When VP8 rewriting is enabled in the bridge, VP8 video produced by Edge is wrongly rendered in Chrome/Firefox.

• GitHub issue: https://github.com/jitsi/lib-jitsi-meet/issues/520

InvalidStateError when calling send() / receive()

Randomly, sending a new track or receiving a new track fails with InvalidStateError. The issue reported in Edge tracker includes a way to reproduce it.

As per conversations with Edge developers, it seems that Edge has some kind of limitation in the number of VP8 streams it can encode/decode at the same time. However, in my tests I’ve been able to send a VP8 stream and receive 5 VP8 streams at the same time.

The problem happens much more often when calling rtpSender.stop() or rtpReceiver.stop() and then creating a new RtpSender or RtpReceiver and calling send() or receive() on it.

• GitHub issue: https://github.com/jitsi/lib-jitsi-meet/issues/519
• Edge issue: https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/12459320/

pc.getStats(): no way to get usable and needed stats

WebRTC stats produced by Edge don’t provide enough information to determine resolution, framerate or bitrate.

• GitHub issue: https://github.com/jitsi/lib-jitsi-meet/issues/523

Device selection does not work

In Edge, the device selector UI shows grayed drop down lists for mic and webcam.

• GitHub issue: https://github.com/jitsi/lib-jitsi-meet/issues/530

Other issues in Edge

Those issues/bugs in Edge do not affect lib-jitsi-meet because the code avoids them. However, for future changes, it’s important to consider them:

• RtpReceiver.track returns a different MediaStreamTrack every time: https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/12399497/