Arch Linux

FGYada

Member

Registered: 2024-10-15

Posts: 9

[SOLVED] [ffmpeg] Update breaks H.264 HW accelerationDolphin's

Hello everyone,

I'm trying to diagnose an issue with Dolphin's embedded player after the recent system updates and would appreciate some help or confirmation from others.

The Problem
After the latest updates, the embedded video player in Dolphin's information panel can no longer play H.264 videos using hardware acceleration. The audio track plays correctly, but the video frame remains black. The terminal outputs the following error when I press play:

[00007ee55c015500] main decoder error: Codec `h264' (H264 - MPEG-4 AVC (part 10)) is not supported.
[00007ee55c015500] main decoder error: Não há suporte a este Codec
[00007ee55c015500] main decoder error: Não foi possível decodificar o formato "h264" (H264 - MPEG-4 AVC (part 10))

I'm running Arch with GNOME, the proprietary NVIDIA driver, and using Dolphin as my file manager.

Diagnostic Steps I've Already Taken

    The problem seems to have started after the recent ffmpeg update around July 15th.

    I've confirmed the issue is specific to the hardware acceleration stack used by Dolphin's player. Forcing software decoding in a dedicated player like MPV (--hwdec=no) works correctly.

    Reinstalling packages (sudo pacman -S ffmpeg x264) did not solve the issue.

    I've run checks to ensure my local hardware acceleration configuration is correct.

Logs and Evidence

The pacolog for ffmpeg shows it was recently rebuilt against glslang:

➜ pacolog ffmpeg
upgpkg: 2:7.1.1-5: glslang 1.4.321.0 rebuild · b504a3f8
Robin Candau authored Jul 15, 2025

vainfo shows that the NVIDIA VA-API driver is initializing correctly and reports support for H.264:

➜ vainfo
Trying display: wayland
vainfo: VA-API version: 1.22 (libva 2.22.0)
vainfo: Driver version: VA-API NVDEC driver [direct backend]
vainfo: Supported profile and entrypoints
VAProfileH264Main           : VAEntrypointVLD
VAProfileH264High           : VAEntrypointVLD
VAProfileH264ConstrainedBaseline: VAEntrypointVLD
... (and other profiles)

ffmpeg also confirms it is aware of the available hardware acceleration methods:

➜ ffmpeg -v verbose -hwaccels
Hardware acceleration methods:
vdpau
cuda
vaapi
qsv
drm
opencl
vulkan

My suspicion

My suspicion is that the ffmpeg update (recompiled against glslang) introduced a regression that specifically breaks the VA-API communication when called from Dolphin's embedded player (or the underlying Qt/KDE framework). The hardware acceleration itself seems to work in other contexts. I'd like to know if anyone else with a similar setup (NVIDIA card, using Qt/KDE applications) has noticed this behavior. Any ideas for a workaround or a bug report I might have missed?

Thanks for your help!

Last edited by FGYada (2025-07-20 16:56:49)

stanczew

Member

Registered: 2021-03-02

Posts: 108

Re: [SOLVED] [ffmpeg] Update breaks H.264 HW accelerationDolphin's

Hi, just a sanity check, what's the output of:

pacman -Q phonon-qt6-backend vlc-plugin-ffmpeg

Last edited by stanczew (2025-07-20 16:39:45)

Lone_Wolf

Administrator

From: Netherlands, Europe

Registered: 2005-10-04

Posts: 14,840

Re: [SOLVED] [ffmpeg] Update breaks H.264 HW accelerationDolphin's

Dolphin doesn't have an embedded video player, it uses the phonon framework to display videos.

Phonon can use several backends, see https://wiki.archlinux.org/title/KDE#Phonon.
Please post the output of pacman -Qs phonon.

Last edited by Lone_Wolf (2025-07-20 16:45:29)

---

Disliking systemd intensely, but not satisfied with alternatives so focusing on taming systemd.

clean chroot building not flexible enough ?
Try clean chroot manager by graysky

FGYada

Member

Registered: 2024-10-15

Posts: 9

Re: [SOLVED] [ffmpeg] Update breaks H.264 HW accelerationDolphin's

Thank you both, @Lone_Wolf and @stanczew. You pointed me in the exact right direction.

The problem was indeed a missing `vlc-plugin-ffmpeg`. After installing it, the embedded player works again.
What made this so confusing is that it was working perfectly before the recent updates, even without this package installed.

It seems the `ffmpeg` update broke the direct VA-API decoding path for the VLC backend, and installing the plugin provided a necessary software-decoding fallback. I appreciate the help in untangling this.

I'll mark the topic as [SOLVED].

Last edited by FGYada (2025-07-20 16:57:18)

Scimmia

Fellow

Registered: 2012-09-01

Posts: 13,630

Re: [SOLVED] [ffmpeg] Update breaks H.264 HW accelerationDolphin's

It seems the `ffmpeg` update broke the direct VA-API decoding path for the VLC backend, and installing the plugin provided a necessary software-decoding fallback. I appreciate the help in untangling this.

Nothing of the sort. The vlc package was split up, and pacman told you about this when you updated. It listed a bunch of new optional deps, but you didn't do anything with them, so it failed. It was always using the ffmpeg plugin when it was part of the vlc package.

hopeseekr

Member

Registered: 2019-12-11

Posts: 5

Re: [SOLVED] [ffmpeg] Update breaks H.264 HW accelerationDolphin's

Thank you@stanczew... My VLC hasn't been playing videos for the first time that I can ever remember.

I was heavy in the DivX and Xvid scenes back in the late 1990s and early 2000s, particularly as the maintainer of the xMule project.

I remember how, in the past, we used to have to worry about which codec any particular video used. This was way before YouTube was a glint in the eye of engineers, when we had to manually go out and look for our stuff. For all the kids, we used to have to run analysis tools in the Windows CLI (because tooling didn't exist in Linux for years) to see what codec was being used, hunt down the codec and install it. Using the codecs didn't exist in Linux and we'd use real hacks to get them running in Wine. back in the Linux 2.6 days.

VLC was released in early 2001 and it's number one advantage was that it included all of the codecs (!!) This was truly revolutionary at the time, and a whole lot of us circa 2002-2006 would teach people to install VLC with the firefox plugin to enable video web for the first time.

Until this last week, I had said good bye to needing to worry about codecs until vlc just started failing to play certain h264 videos, particularly those I use the most: Those downloaded by yt-dlp and youtube-dl.

This is a bad reversion and goes against the core ethos of VLC and is a net negative for the Arch experience.

Someone needs to make it go back to the way it was. I've been an Arch user for many years, and I never read those "upgrade notes" @Scimmia speaks of.

If it's such a breaking change that goes against a program's leading ethos, perhaps require the user to read the notice and press "Y" or something.

Scimmia

Fellow

Registered: 2012-09-01

Posts: 13,630

Re: [SOLVED] [ffmpeg] Update breaks H.264 HW accelerationDolphin's

I've been an Arch user for many years, and I never read those "upgrade notes" @Scimmia speaks of.

Hopefully you've learned something from this experience, then. If you ignore what pacman tells you, things breaking is normal and expected.

V1del

Forum Moderator

Registered: 2012-10-16

Posts: 25,076

Re: [SOLVED] [ffmpeg] Update breaks H.264 HW accelerationDolphin's

And if you want the "all inclusive" experience there's vlc-plugins-all which depends on all the sub packages. I'm not sure why you feel this is such a huge deal. There have been complaints that the VLC package was too fat because it's lib is a core dependency of stuff (e.g. case in point plasma/dolphin needs a vlc dependency, some people don't actually use the preview feature and were complaining that vlc was too big of a dependency) now that the split was made you have the reverse side of the coin complaining they need to install more distinct packages.