Failed to initialize VapourSynth

[tunaflsh]

mpv Information

mpv v0.41.0-603-g333857403 Copyright © 2000-2026 mpv/MPlayer/mplayer2 projects
libplacebo version: v7.360.1
FFmpeg version: N-124396-g7fc335cb27
FFmpeg library versions:
   libavcodec      62.30.100
   libavdevice     62.4.100
   libavfilter     11.17.100
   libavformat     62.15.100
   libavutil       60.30.100
   libswresample   6.4.100
   libswscale      9.7.100

Other Information

- Linux version: Arch Linux
- Kernel Version: Linux 7.0.3-zen1-2-zen
- GPU Model: NVIDIA GeForce GTX 1660 Ti Mobile, Radeon Vega Mobile Series
- Mesa/GPU Driver Version: OpenGL 4.6, vulkan 595.71.05, Mesa 26.0.6-arch1.1
- Window Manager and Version: niri 26.04 (v26.04-16-g1f07cffa)
- Source of mpv: [aur/mpv-full-git](https://aur.archlinux.org/packages/mpv-full-git) and [extra/mpv](https://archlinux.org/packages/extra/x86_64/mpv/)
- Latest known working version: not sure
- Issue started after the following happened: vapoursynth R75

Reproduction Steps

cat <<EOF > test.vpy
import vapoursynth as vs
core = vs.core
video_in.set_output()
EOF
vapoursynth config
mpv --no-config --vf=vapoursynth=file=test.vpy Videos/2026-03-29_15-44-30.mp4

Expected Behavior

WORKAROUND

% VSSCRIPT_PATH=$(vapoursynth get-vsscript) mpv --no-config --vf=vapoursynth=file=test.vpy Videos/2026-03-29_15-44-30.mp4
[ffmpeg/demuxer] mov,mp4,m4a,3gp,3g2,mj2: UDTA parsing failed retrying raw
● Video  --vid=1  (h264 2560x1440 60 fps 4846 kbps) [default]
● Audio  --aid=1  (opus 2ch 48000 Hz 1 kbps) [default]
AO: [pipewire] 48000Hz stereo 2ch floatp
VO: [gpu-next] 2560x1440 yuv420p
AV: 00:00:01 / 00:00:16 (6%) A-V:  0.000 Dropped: 2
Exiting... (Quit)

Actual Behavior

[ffmpeg/demuxer] mov,mp4,m4a,3gp,3g2,mj2: UDTA parsing failed retrying raw
● Video  --vid=1  (h264 2560x1440 60 fps 4846 kbps) [default]
● Audio  --aid=1  (opus 2ch 48000 Hz 1 kbps) [default]
[vapoursynth] Failed to initialize VapourSynth VSScript library: Python executable and library path couldn't be determined despite automatic configuration. Run `vapoursynth config` to set it for this Python installation and then try again.
[user_filter_wrapper] Creating filter 'vapoursynth' failed.
Video: no video
AO: [pipewire] 48000Hz stereo 2ch floatp
A: 00:00:02 / 00:00:16 (13%)
Exiting... (Quit)

Log File

output.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.

[tunaflsh]

vspipe -v works fine. And this works too:

cat <<EOF > test_isolated.vpy
import vapoursynth as vs
core = vs.core
clip = core.std.BlankClip(width=1920, height=1080, fpsnum=60, fpsden=1, length=100)
clip.set_output()
EOF
vspipe --info test.vpy

The output:

Output Index: 0
Type: Video
Width: 1920
Height: 1080
Frames: 100
FPS: 60/1 (60.000 fps)
Format Name: RGB24
Color Family: RGB
Alpha: No
Sample Type: Integer
Bits: 8
SubSampling W: 0
SubSampling H: 0

[kasper93]

/cc @CrendKing

[CrendKing]

Since you are using VapourSynth R75, where it is installed as Python package, you need to add that VSSCRIPT_PATH to your environment variable per installation documentation(step 5 on Linux). I think it is marked as optional because not everyone use VapourSynth as third-party module, as you demonstrated you can vspipe. But if you use VapourSynth from mpv, it is required.

Ideally the OS packagers would be able to make this step automated during package installation. Maybe you could contact AUR maintainer and see if they can help.