gpu-next screenshot fails with ewa filter functions on SDR and Dolby Vision

[Neurognostic]

Important Information

$ mpv --version
mpv v0.37.0-484-g665a472098 Copyright © 2000-2024 mpv/MPlayer/mplayer2 projects
libplacebo version: v6.338.2
FFmpeg version: N-113989-gd34e9a81b1
FFmpeg library versions:
   libavutil       58.40.100
   libavcodec      60.41.100
   libavformat     60.24.100
   libswscale      7.6.100
   libavfilter     9.17.100
   libswresample   4.14.100

Arch Linux BSPWM 0.9.10-51-gaf3bd8b Locally compiled with mpv-full-git^AUR NVIDIA 3070 Ti, 550.54.14

Reproduction steps

1. Choose an SDR or Dolby Vision $VIDEO

2.  mpv --no-config --vo=gpu-next --scale=ewa_lanczos $VIDEO
    mpv --no-config --vo=gpu-next --scale=ewa_lanczossharp $VIDEO
    mpv --no-config --vo=gpu-next --scale=ewa_lanczos4sharpest $VIDEO
   

3. Use screenshot or screenshot video input mode commands.
4. Observe blank screenshots taken

📝 Note: Any non-EWA filter function works fine, but scale=ewa_lanczossharp is used by both --profile=gpu-hq & --profile=high-quality which is how I first noticed the issue.

Expected behavior

Take a screenshot with gpu-next when using --scale=ewa_lanczossharp.

Actual behavior

When viewing an SDR or Dolby Vision video with --vo=gpu-next and taking a screenshot with any ewa_* filter function set as --scale results in screenshots with the correct resolution, but completely black-filled.

Does not seem to occur with HDR10 video (common on YouTube).

The same result is seen with every --hwdec option available to me, including --hwdec=no.

I tried compiling without zimg (-Dzimg=disabled), but got the same result.

📝 NOTE: The screenshot window input mode command does work as expected, but screenshot video has the same broken behavior as screenshot.

Input Command	Format	chk
screenshot	SDR	❌
screenshot	DV	❌
screenshot	HDR10	✅
screenshot video	SDR	❌
screenshot video	DV	❌
screenshot video	HDR10	✅
screenshot window	SDR	✅
screenshot window	DV	✅
screenshot window	HDR10	✅

Log file

Logs show an example of taking a screenshot of an SDR video.

output.txt

With zimg disabled:

output_nozimg.txt

Workaround

Using --screenshot-sw=yes allows screenshot input mode command to work with SDR and Dolby Vision video, however the screenshot window result is stretched and distorted when using vo=gpu-next with screen-shot-sw=yes.

I did not do testing to see if the colors were accurate with this workaround and HDR video.