From github: https://github.com/webcompat/web-bugs/issues/132899.

<!-- @browser: Firefox 122.0 -->
<!-- @ua_header: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:122.0) Gecko/20100101 Firefox/122.0 -->
<!-- @reported_with: unknown -->

URL: https://www.youtube.com/

Browser / Version: Firefox 122.0
Operating System: Windows 11
Tested Another Browser: Yes Edge

Problem type: Something else
Description: Persistent YouTube Playback Issues on Robust Machines: Exclusive to Firefox
Steps to Reproduce:
Trialled on three robust machines boasting a minimum of 32GB RAM each, with two featuring i7 processors and one equipped with an i9 processor. Despite the fact that the newest machine is a mere few months old and oldest machine is circa two years old, persistent stuttering and freezing issues plague YouTube playback.

It's important to note that all devices underwent testing on a fibre 1GB up/down connection via Ethernet, ruling out buffering as the culprit. (Also tested extensively on wifi, to no success). Intriguingly, this problem is exclusive to Firefox, as no such anomalies were observed in Chromium Edge.

This issue has been verified across three distinct devices, and anecdotal evidence from various online communities, including Reddit and other forums, indicates that others are encountering the same/similar issue.

I have attempted diagnosing, i.e. fresh Firefox install, or no FF plugins. All drivers are up-to-date on all three machines. This issue has been occurring for the last few Firefox versions - kept faith with 122 it would finally be repaired, but sadly not.

At the point when YouTube is stuttering/freezing, audio typically continues to work. I have checked CPU usage and Memory usage, however usage is only 20%.

Strange thing is, sometimes, it works flawlessly i.e. run 4 or 5 simultaneous 8k Streams from YouTube with no freezing or stuttering - hence I am unable to pinpoint what it specifically is.

Could it be a Codec issue? It's usually using VP09 when issue persists.

<details>
<summary>Browser Configuration</summary>
<ul>
<li>Firefox 122.0 | Windows 11</li>
</ul>
</details>

From webcompat.com with ❤️

Change performed by the Move to Bugzilla add-on.

The issue was reported via webcompat.com reporter. We are not able to reproduce the issue (most likely an add-on is causing it), but based on the discussion we recently had with the other teams, issues reported that involve audio/video failing on top sites, we have moved the issue accordingly for further investigations. Please feel free to move the issue to the relevant product and component, or to close the issue if it is not reproducible on your side.

Answered on GitHub, so this reaches the reporter. Thanks for filing here.

Reporter, when you can reproduce, it would help a lot if you could record performances using the Firefox Profiler (nothing to install, easy to do). Video + text instructions are here: https://blog.paul.cx/post/profiling-firefox-media-workloads/#the-media-preset

If you can then upload the profile and post the URL here, or save it and send it privately at padenot@mozilla.com, we can take a look and understand what's going on. I agree that this type of machine should be fast enough to always comfortably play even the most demanding media file.

I'm experiencing the same issue with VP9 playback on Youtube. Most videos play fine, but occasionally a longer video will freeze and drop hundreds of frames even though the progress bar shows sufficient buffer ahead.

I enabled profiling and waited for the issue to re-occur. I then captured a profile from that point via hotkey. Playback continued by its self roughly 20 seconds after the point of failure.

https://share.firefox.dev/3w5qPvl

As far as I can recall this issue started within the last 30 days.

Ali, thanks a lot for following up. When this happens, does the rest of the page, or the rest of the browser work as it should, or is everything frozen?

No worries. Yes, the page, browser and video player remain functional when the video stops.

Have had this happen a few more times.
https://share.firefox.dev/49erZ6t
https://share.firefox.dev/3HYspSs
https://share.firefox.dev/3SWID4U

One of the times the audio continued while the video was frozen.
https://share.firefox.dev/49x0nJr

The web compat discussions seems the same as the bug 1878510, let's keep all discussion together.