Bug#1021032: vlc: playing videos results in a black screen

[Rémi Denis-Courmont <remi@remlab.net>]

Le lauantaina 8. lokakuuta 2022, 12.40.56 EEST KeyofBlueS a écrit :
> Hi all. Let's continue here from #1021140
> <https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1021140>
> 
> It seems this issue it's not completely fixed. Before it was always
> reproducible under any circumstance, when now there are at least two ways
> to always trigger it:

I believe that the issue is not fixed at all.

The symptoms started showing up after Debian updated Qt, and affect only the Qt 
GUI. The last attempt to fix it affected the VA-API video decoding path in such 
a way that it will still *fail* at a different pace than it did before the fix. 
Then it will fallback to VDPAU or to software decoding path.

But it will still fail anyhow, and the exact same failure occurs when playing 
video outside the VLC GUI, which is unaffected. Therefore, I am led to believe 
that this is a race condition that became apparent with the Debian Qt update, 
and partially worked around by the last VA change in the Debian VLC packaging.


It would be interesting to see if it reproduces with VLC <= 3.0.12 and >= 
3.0.18~rc1. If not, then the X11 protocol-level race condition with parenting 
the VLC video window would be the obvious culprit. Unfortunately though, I 
reckon that that is in fact an X11 protocol design issue that is unfixable 
(short of switching to Wayland, basically), though there are potential 
workarounds.

It could also be something else. I don't pretend to know that.

-- 
レミ・デニ-クールモン
http://www.remlab.net/