Closed Bug 1300169 Opened 5 years ago Closed 5 years ago

MediaRecorder video and audio are very out of sync


(Core :: Audio/Video: Recording, defect, P1)

51 Branch





(Reporter: zach, Unassigned)


(Keywords: regression, regressionwindow-wanted)

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/52.0.2743.116 Safari/537.36

Steps to reproduce:

Using the Firefox Nightly 51.0a1 (2016-09-02) with the example recorder at I set the Time interval to 50000 and clicked "Start". I snapped the clap board several times saying the word "snap" each time. I also counted down from 10 holding up fingers (mod 5) to show what number I was saying. 

Actual results:

You can see that the audio lags behind the video by about 1 second. The sound of the clap board, the sync of the lips, and the sync with the fingers is all evidence of how far off it is. 

This problem did not exist on FF47.

FF48 introduced a different timestamp bug but the resolution of that bug has left this syncing problem in place. 

Expected results:

The audio and video should be in sync. The snap sound should happen at the moment the clap board closes, the fingers should reflect the number I am saying (mod 5), and my lips should sync with the words I am saying.
Here is an example recorded using Nightly 2016-09-02:

Here is an example recorded using Beta 49.0b6:

The bug is in Nightly but NOT in Beta. The a/v sync in Beta seems ok.
This bug does NOT occur in Developers Edition 50.0a2 (2016-09-02).
Severity: normal → major
OS: Unspecified → Mac OS X
Component: Untriaged → WebRTC: Audio/Video
Product: Firefox → Core
Component: WebRTC: Audio/Video → Audio/Video: Recording
Rank: 15
Priority: -- → P1
Someone cloned this as a win10 bug, so I think it's all platforms.
OS: Mac OS X → All
(In reply to zach from comment #3)
> Someone cloned this as a win10 bug, so I think it's all platforms.
Closed: 5 years ago
Resolution: --- → DUPLICATE
Duplicate of bug: 1300871
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