Fix: Firefox connectivity issues caused by PR694

[lukehb]

Relevant components:

• Frontend library

Problem statement:

As a result of #694 sometimes Firefox was unable to connect. It would error with uncaught (in promise) DOMException: Cannot set ICE candidate for level=<Nothing> mid=: No such transceiver.

Solution

This PR patches the previous fix by hard coding the sdpMLineIndex to 0 which resolves the issue on Firefox and maintains working connectivity on the other browsers. This change means we assume:

1. Bundle is being used for WebRTC media
2. The master media line of the bundle is in index 0.

Both of these assumptions hold for all versions of Pixel Streaming 1 and 2 to date.

Documentation

N/A - This is very implementation specific, but this PR should serve as a good record.

Test Plan and Compatibility

Tested:

Chrome + AWS
Chrome + TailScale
Firefox + AWS
FireFox + TailScale
Safari + AWS
Safari + TailScale

All these combinations were able to stream correctly.

[changeset-bot]

🦋 Changeset detected

Latest commit: 39d76ab

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@epicgames-ps/lib-pixelstreamingfrontend-ue5.7	Patch

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[github-actions]

💚 All backports created successfully

Status	Branch	Result
✅	UE5.6
✅	UE5.7

Note: Successful backport PRs will be merged automatically after passing CI.

Questions ?

Please refer to the Backport tool documentation and see the Github Action logs for details

[lukehb]

If this turns out to be an issue because bundle master is no longer 0 we can get bundle master using something like:

const bundleMasterMid = sdp.match(/^a=group:BUNDLE (.*)$/m)[1].split(" ")[0];

Then we can just always add a candidate with that mid, the immediately after, add another candidate with whatever the real mid was. It is a little wasteful in terms of adding known failing ice candidates, but it should fix the issue.