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.

[Traneptora]

Looks like it may be an issue with --gpu-api=opengl which is the default. If you use --gpu-api=vulkan, I can't reproduce it. Can you?

[guidocella]

I can also only reproduce this on Nvidia+OpenGL.

[Neurognostic]

I cannot reproduce the issue with --gpu-api=vulkan. All three screenshot input mode commands works as expected with all three tested formats: SDR, HDR10, and Dolby Vision.

mpv --no-config --vo=gpu-next --gpu-api=vulkan --scale=ewa_lanczos $VIDEO

This is a good enough a fix for my use case. I do not require opengl.

[na-na-hi]

This is also reproducible on Windows with Nvidia+OpenGL. Using ewa scaler also causes black frame after resizing and sometimes after toggling stats, on both Windows and Linux.

[kasper93]

I would debug that, but I don't have NVIDIA gpu and seem to does not happen on AMD in any platform I tested. It is probably fixable if we understand what exactly causes screenshot render to fail.

[guidocella]

This is caused by --cscale=ewa_lanczossharp specifically instead of --scale. Also when taking png, webp or jxl screenshots with a transparent background, the screenshots are transparent instead of black.

This is also reproducible on Windows with Nvidia+OpenGL. Using ewa scaler also causes black frame after resizing and sometimes after toggling stats, on both Windows and Linux.

If you resize while paused the video actually disappears until you play again. Also with --video-sync=display-resample it shows a black frame after every seek. With --background-color=0/0 in mpv.conf it shows the wallpaper instead when zooming out and seeking, but not if you set --background-color at runtime or zoom in, and it doesn't show background colors other than black otherwise.

[guidocella]

https://github.com/mpv-player/mpv/issues/11499#issuecomment-2380425327 prevents the bug.