Regression: `--background=tiles` shows solid black instead of checkerboard on `vo=gpu-next` (works fine on `vo=gpu`)

mpv Information

mpv v0.41.0-1012-ge8673660a Copyright © 2000-2026 mpv/MPlayer/mplayer2 projects
 built on Aug 29 2026 00:29:12
libplacebo version: v7.371.0 (v7.360.0-118-g41ac298-dirty)
FFmpeg version: N-126314-g3386acd2f
FFmpeg library versions:
   libavcodec      63.8.101
   libavdevice     63.2.100
   libavfilter     12.3.101
   libavformat     63.6.100
   libavutil       61.6.100
   libswresample   7.2.100
   libswscale      10.2.100

Other Information

- Windows version: Windows 11
- GPU model, driver and version: NVIDIA
- Source of mpv: Windows build
- Latest known working version: mpv v0.41.0-dev-g41f6a6450 (Built on Dec 21 2025)
- Issue started after the following happened: Upgrading to recent 2026 builds.

Reproduction Steps

Expected behavior

When playing a video with an alpha channel (e.g. MOV Animation or WebM yuva420p), using --background=tiles should render a checkerboard pattern behind the transparent video.

Actual behavior

With --vo=gpu-next, the background renders as solid black instead of tiles.
However, switching to --vo=gpu renders the checkerboard perfectly on the exact same build.
This seems to be a regression in gpu-next / libplacebo handling of alpha/tiles, or possibly related to the recent FFmpeg 9.0/libavcodec 63 update which seems to drop A=straight metadata for some files.

Reproduction steps

1. Open a video with transparency.
2. Run: mpv --no-config --background=tiles --vo=gpu-next video.mov -> (Result: Solid Black)
3. Run: mpv --no-config --background=tiles --vo=gpu video.mov -> (Result: Checkerboard appears correctly)

input.zip

Expected Behavior

When playing a video with an alpha channel (like MOV Animation or WebM yuva420p), using the --background=tiles option should render a checkerboard pattern behind the transparent video to indicate transparency.

Actual Behavior

With --vo=gpu-next, the background renders as solid black instead of the expected tiles.
However, switching the renderer to --vo=gpu renders the checkerboard perfectly on the exact same build.
This seems to be a regression in how gpu-next or libplacebo handles alpha/tiles, or possibly related to the recent FFmpeg 9.0/libavcodec 63 update which seems to drop A=straight metadata for some files during decoding.

Reproduction steps:

1. Open a video with transparency (e.g. MOV).
2. Run: mpv --no-config --background=tiles --vo=gpu-next video.mov (Result: Solid Black)
3. Run: mpv --no-config --background=tiles --vo=gpu video.mov (Result: Checkerboard appears correctly)

Log File

mpv_log.txt

Sample Files

No response

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

• I tested and confirmed that the issue exists with the latest release version or newer.
• 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.

Reproduce the issue with the attached input.zip using --background=tiles and compare --vo=gpu-next against --vo=gpu, then read mpv_log.txt for the rendering and alpha-handling differences. Done means the transparent video shows the checkerboard with --vo=gpu-next as it does with --vo=gpu, without regressing the existing renderer.