Vapoursynth not reinitialized on display change

Important Information

Requires Vapoursynth.

Official shinchiro Windows nightly.

mpv 0.32.0-258-g281f5c63c1 Copyright © 2000-2020 mpv/MPlayer/mplayer2 projects
built on Sun Mar 15 22:10:08 +08 2020
FFmpeg library versions:
libavutil 56.42.100
libavcodec 58.75.100
libavformat 58.41.100
libswscale 5.6.101
libavfilter 7.77.100
libswresample 3.6.100
FFmpeg version: git-2020-03-14-425b6a9a2

Windows 10 Pro 1909 18363.720

Reproduction steps

1. Enable vapoursynth in Windows with script changing FPS based on display_fps.
2. Move the window to another display or start it with -fs-screen=
3. Note the downsampling ratio is wrong and is corrected when seek happens.

Note: Used to be fine in very old builds, but cannot remember when - probably in December.

Expected behavior

Vapoursynth is reinitialized when window switches displays, including starting fullscreen on a different displays, and/or is provided updated display_fps.

Actual behavior

Vapoursynth is not reinitialized, display_fps is incorrect when window is moved to a different display.

Log file

vapoursynth-display-fps.txt
svp.py.txt

Start by reproducing the issue with Vapoursynth on Windows 10, moving the window between displays or using -fs-screen, and review the attached vapoursynth-display-fps.txt and svp.py.txt files. Trace how display_fps changes reach Vapoursynth and how display changes trigger reinitialization. Done means the script receives the correct display_fps after a display switch or fullscreen startup, without requiring a seek.