Fix Pixel Streaming intermittently fails to make a network connection even with correct ICE candidates #694
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…ections to fail, these can be safely dropped as we use bundle by default and therefore these attributes are not used.
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lukehb
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lukehb
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Sep 11, 2025
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| const remoteIceCandidate = new RTCIceCandidate({ | ||
| candidate: iceCandidateInit.candidate, | ||
| sdpMid: '' | ||
| }); |
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Relevant components:
Problem statement:
In some instances Pixel Streaming/WebRTC will fail to make a network connection even if the relevant ICE candidates are present. This behaviour manifests with certain connections (often Windows UE running on a slow machine where
srflxis required on both sides) and if the connection is repeatedly retried it will intermittently connect. See: #692Solution
Through investigation it was found that:
sdpMidandsdpMLineIndexsdpMidandsdpMLineIndexare not required if usingbundlemode (where media is multiplexed over one transport)bundleis Pixel Streaming's default (and only supported mode) for WebRTC connectionssdpMidcan be set to an empty string""andsdpMLineIndexcan be omitted and the connection can proceed normallyWhile the WebRTC spec says candidates can be trickled in any order, we observed that if a candidate containing
sdpMid:n(where n is any value other than the master bundle, e.g.0in our case) was received before the candidate containingsdpMid:m(where m is the master bundle, e.g.0) then the connection would fail. The fix was simply to remove this unnecessary information and the connection proceeds as it should and is able to connect.Documentation
N/A - though it should be noted with this change we explicitly are making the assumption now that Pixel Streaming must use
bundle- which has always been an implicit assumption anyway.Test Plan and Compatibility
I tested this PR on the following browsers/devices:
Chrome + Windows
Firefox + Windows
Chrome + iPhone
Chrome + Mac
Chrome + iPad
Safari + iPhone
Safari + Mac
Safari + iPad
Chrome + Android
Android Browser + Android