Firefox A/V Sync Issues
macOS 14.1.1 on an M2 with FF 120.
When going to sites such as nbcnews.com/now or https://toronto.ctvnews.ca, A/V sync is off by about a second.
This appears to be due to the volume being muted when video playback starts. Unpausing the video leads to the video freezing for a very brief moment, then the A/V sync is clearly incorrect.
This can be replicated on YouTube by loading a video, muting the video (if not muted already), refreshing the page (F5), allowing the video to play, then unmuting the video. The sync will be incorrect.
If the audio is unmuted when the video play back starts, this does not appear to happen.
Following this article has no impact: https://support.mozilla.org/en-US/kb/performance-settings, nor does setting media.hardware-video-decoding.enabled to false.
This issue does not occur on Microsoft Edge.
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Does it still happen in a new profile? An easy way to test a new profile is to install Developer Edition and see if it happens there or refresh your existing profile.
Yes, it happens in a new profile. I also installed the Dev Edt and it happens there, as well.
This is easier to reproduce than I thought. Going to the live feed on https://toronto.ctvnews.ca/ (though not restricted to the site, CNN, MSNBC, and others experience the same issue), if the video is unmuted to start with, simply mute it. When you unmute it, the video freezes for ~1 second. The audio begins slightly prior to the video.
You can repeated mute/unmute to further desync the audio and video.
And it looks like I have a solution, found at https://www.reddit.com/r/firefox/comments/11i6i1f/possible_fixworkaround_for_twitch_audio_desync/.
The config setting "media.suspend-bkgnd-video.enabled" needed to be set to false (I had to create the setting).
Despite the name of this setting, this impacted non-background full screen video on non-YouTube sites.
Sadly, spoke too soon. This issue continues, unmuting the (small) video player on nbcnews.com triggered it.
Back to Edge, unfortunately.
media.suspend-bkgnd-video.enabled won't work in 120 as since 117 all bkgnd prefs have been changed to background to make their name clearer and that is the reason that you had to create it.
- media.suspend-background-video.enabled
So there is another reason for why it works better in 120.
- 1840980 - Rename media.resume-bkgnd-video-on-tabhover, media.suspend-bkgnd-video.delay-ms, and media.suspend-bkgnd-video.enabled prefs [117][bkgnd=>background]
Thanks, setting media.suspend-background-video.enabled to false does not resolve it.
Does it still happen after rebooting the system and before starting any other applications?
Yes, it continues to happen. It also happens in Firefox troubleshooting mode as well as after a full FF reset.
I think I may have narrowed it down. I'm using an LG Ultrafine 4K connected via Thunderbolt. I typically use the speakers on the monitor, and I think that is what is causing the A/V sync issue. I tested using the MBA not connected to the monitor and I could not reproduce. I connected it back to the monitor, but used the MBA internal output and could not reproduce the issue. When I switched back to the monitor's speakers, I was able to reproduce.
I'm not sure where to go from here. This is the only application I experience this type of audio/video sync issue with. Other browsers, Davinci Resolve, QuickTime, Apple TV/Music, etc. work without sync issues.
Monitor firmware is current; there is no OSD to adjust the monitor settings. The monitor is connected via Thunderbolt.
Monitor model: https://www.lg.com/us/business/computer-monitors/lg-24md4klb-b