[Webkit-unassigned] [Bug 257803] New: Terrible video quality when using TransformStream with Simulcast

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=257803

            Bug ID: 257803
           Summary: Terrible video quality when using TransformStream with
                    Simulcast
           Product: WebKit
           Version: Safari 16
          Hardware: All
                OS: All
            Status: NEW
          Severity: Critical
          Priority: P2
         Component: WebRTC
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: pminchev at digitalsamba.com
                CC: youennf at gmail.com

Created attachment 466619

  --> https://bugs.webkit.org/attachment.cgi?id=466619&action=review

The crazy jitter value coming from the Peer Connection Stats

1. Have a WebRTC app which publishes/receives simulcast streams (through a SFU media server).

2. Have a TransformStream in a worker which just passes unmodified the stream (RTCRtpScriptTransform):

    const transformStream = new TransformStream({
      transform: async (chunk, controller) => {
        controller.enqueue(chunk); //Unmodified chunk
      }
    })

3. Observe the received video quality is pixelated and terrible.

4. Observe only the L layer 320x180 remains with a very high bitrate and suddenly jitter value in PeerConnection stats becomes HUGE:
   7737 seconds - 2 hours which is practically an impossible value.

   Attaching screenshots.

If simulcast is not used, then video quality is fine, but the moment simulcast and a TransformStream is used, the quality goes bad and jitter of 2 hours appears.

Jitsi (a videoconference provider) also experiences this issue on Safari -> https://community.jitsi.org/t/e2ee-on-ios-safari-with-enableencodedtransformsupport/114517/9

So it seems a widespread issue under Safari.

Under Chrome on MacOS everything is fine (with the same SFU media server, simulcast and Insertable Streams). So that seems to confirm it is a Safari/Webkit issue.

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