2089482 - Microphones are enumerated twice when cameras are enumerated

Status: ASSIGNED

(Core :: Audio/Video, defect)

Description

[Sylvestre Ledru [:Sylvestre]]

MediaManager::EnumerateRawDevices tries to reuse the microphone list for camera groupId correlation when audio and video use the same backend (micsOfVideoBackend). Since bug 1528042 moved microphone enumeration before cameras, audioBackend == videoBackend is evaluated before videoBackend is assigned, so it is always false and the microphones are enumerated a second time for every camera enumeration (enumerateDevices(), getUserMedia()).

Fix: pick videoBackend before the audio block. The existing MOZ_ASSERT on the forced microphone name in the reuse path holds, because both names come from the same media.audio_loopback_dev read.

Performance only. Found by Coverity Scan (CID 1559893, reported as a dereference after null check).

Comment 1

[Sylvestre Ledru [:Sylvestre]]

Attachment: Bug 2089482 - Pick the video backend before enumerating microphones in MediaManager::EnumerateRawDevices (Coverity CID 1559893) r?karlt

Since microphones are enumerated before cameras, audioBackend was
compared with a still-null videoBackend, so the microphone list was never
reused for camera groupId correlation and was enumerated a second time.

Comment 2

[BugBot [:suhaib / :marco]]

Set release status flags based on info from the regressing bug 1528042