`hwdec=vaapi` not working with `vo=dmabuf-wayland` on my system

mpv Information

mpv v0.40.0-dirty Copyright © 2000-2025 mpv/MPlayer/mplayer2 projects
 built on Apr  4 2025 07:28:54
libplacebo version: v7.349.0
FFmpeg version: n7.1
FFmpeg library versions:
   libavcodec      61.19.100
   libavdevice     61.3.100
   libavfilter     10.4.100
   libavformat     61.7.100
   libavutil       59.39.100
   libswresample   5.3.100
   libswscale      8.3.100

Other Information

- Linux version:`"Arch Linux"`
- Kernel Version:`Linux Korialo-Arch 6.14.1-273-tkg-eevdf #1 SMP PREEMPT_DYNAMIC TKG Wed, 09 Apr 2025 09:49:46 +0000 x86_64 GNU/Linux`
- GPU Model:`00:02.0 VGA compatible controller [0300]: Intel Corporation CometLake-H GT2 [UHD Graphics] [8086:9bc4] (rev 05)`
- Mesa/GPU Driver Version:`OpenGL version string: 4.6 (Compatibility Profile) Mesa 25.0.3-arch1.1`
- Window Manager and Version:`Hyprland 0.48.1 built from branch  at commit 29e2e59fdbab8ed2cc23a20e3c6043d5decb5cdc  (version: bump to v0.48.1).`
- Source of mpv:`pacman`
- Latest known working version:`v0.39`
- Issue started after the following happened:`update`

Reproduction Steps

No hardware acceleration happens, throws error, and video plays.

 mpv --no-config --vo=dmabuf-wayland --hwdec=vaapi  'https://www.twitch.tv/videos/2314819556?collection=bL1PZGrMDBgM6Q'

Hardware accelerated(?), no errors, video plays normally.

 mpv --no-config --vo=dmabuf-wayland --hwdec=vaapi  --vf=format=fmt=nv12 'https://www.twitch.tv/videos/2314819556?collection=bL1PZGrMDBgM6Q'

Expected Behavior

vaapi should work without this workaround --vf=format=fmt=nv12

Actual Behavior

No hardware acceleration.

Log File

Case - 1 Debug without workaround

test_1.log

Case - 2 Debug with the workaround

test_2.log

Sample Files

No response

I carefully read all instruction and confirm that I did the following:

• I tested with the latest mpv version to validate that the issue is not already fixed.
• I provided all required information including system and mpv version.
• I produced the log file with the exact same set of files, parameters, and conditions used in "Reproduction Steps", with the addition of --log-file=output.txt.
• I produced the log file while the behaviors described in "Actual Behavior" were actively observed.
• I attached the full, untruncated log file.
• I attached the backtrace in the case of a crash.

Run the two exact mpv commands from the issue and compare test_1.log with test_2.log, focusing on the dmabuf-wayland and vaapi behavior. Trace where the format workaround changes negotiation; done means the command without --vf=format=fmt=nv12 uses hardware acceleration without errors.