fix(web): emit a new MediaStream ref per track so Firefox renders screen share#28
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…een share Web SFU viewers showed camera/black instead of the host's screen share on Firefox. useWebRTCSFU mutated one MediaStream and called setRemoteStream with the same object reference on each TrackSubscribed, so React bailed on the re-render and VideoViewer's srcObject effect (dep [stream]) never re-ran. Firefox does NOT render a track added to a MediaStream already attached to a <video> element — and audio is usually subscribed before the screen-share video — so the video never appeared (Chrome tolerated it, hence egress was fine). Now emit a fresh MediaStream reference on every track add/remove so srcObject re-binds. Updated the test, which had asserted the buggy same-ref. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
vu1nz Security Review0 finding(s) in PR #? No security issues found. |
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Bug
Joining a session on the web showed camera + black instead of the host's screen share — on Firefox. The host was publishing SCREEN_SHARE video (the egress composited it fine), and the viewer subscribed; it just never rendered.
Root cause
useWebRTCSFUkept oneMediaStreamand mutated it on eachTrackSubscribed, callingsetRemoteStream(stream)with the same object reference. React bails onsetStatewith an unchanged reference, soVideoViewer'ssrcObjecteffect (dep [stream]) never re-ran. Firefox does not render a track added to aMediaStreamthat's already attached to a<video>element — and audio is usually subscribed before the screen-share video — so the video never appeared. Chrome tolerates the live mutation, which is why the egress (Chrome) was fine.Fix
Emit a fresh
MediaStreamreference on every track add/remove, soremoteStreamchanges identity → React re-renders →srcObjectre-binds → Firefox renders the screen share.Test
The existing test had actually asserted the buggy same-reference behavior (
toBe(firstStream)); updated it to assert a new reference each time, with the correct track contents after add and unsubscribe. Passes; lint clean.🤖 Generated with Claude Code