balko
February 18, 2026, 10:57am
6
Unsolvable. This video will not be played smoothly on any CPU in Qubes OS:VIDEO
The problem is in Xen/Qubes OS rendering approach. It does not depend on CPU that much.
But in R4.3 (fedora-40+ templates) there is a major bug - video playback is choppy in Firefox.
opened 03:36AM - 29 Oct 25 UTC
C: Fedora
P: default
needs diagnosis
affects-4.2
affects-4.3
### Qubes OS release
R4.2.
### Brief summary
YouTube and other video playback i… n Firefox got major regression in fedora-40/41/42 templates: the video gets micro-lags, it looks like the video output in fullscreen becomes like 10 fps instead of 30-60.
Changing template from fedora-39-* to fedora-40-* or later brings this problem.
I tried `fedora-39` (official template) and YouTube playback in Firefox (v119) in full-screen was smooth and flawless.
When template is changed to `fedora-40-xfce` (also official template) playback in Firefox (v132) in the same qube, the same firefox user profile in full-screen the playback is LOW fps, like 10 frames per second or something instead of 30-60. The same happens with fedora-42.
So, I can confirm, that regression happened between fedora-39 and fedora-40, between R4.1 and R4.1 Qubes OS.
### Steps to reproduce
* Install fedora-39 and fedora-42 templates.
* Create 2 qubes with those templates accordingly.
* Play fullscreen YouTube video in both qubes in Firefox. I used 1080@60 video on 1440p display.
### Expected behavior
Video playback is without lags in both qubes.
### Actual behavior
Video playback is kind of laggy in `fedora-42` one, with micro-lags brinnging framerate to like 10 fps instead of 30-60.
`fedora-39` has way smoother playback on the same hardware and everything else.
### Workaround
Using flatpak Firefox instead of default one in Qubes OS workarounds the issue.
I installed flatpak version of Firefox and checked that YouTube playback on fedora-42 in flatpak version of Firefox is smooth (like it was on fedora-39). In the same qube when I open the same video on the same hardware but in native fedora firefox it is much worse (low-fps playback).
### Additional information
* I suspect codecs/libs problem. But I do not know how to force firefox in fedora-42 template to use the same "good" codecs as flatpak version does. I mean I installed RPMFusion and media sections from it, including ffmpeg instead of ffmpeg-free, but it did not improve playback in native firefox.
* 99% of Qubes OS users are probably affected by this issue, and think that lags (low frame rate) of playback is a problem of Qubes OS or weak CPU, but in fact it isn't.