[BUG] Vapoursynth: Color shift on PNG export

[Selur]

Import any video (I mostly work with h264 mp4)

No resolution, color space, bit depth, etc. info.

then output via Vapoursynth to RAW/PNG

You mean by using: Base->Processing->Video ?
Look at the job queue, is Vapoursynth really used?

Right now, the fix/workaround is to set the ColorMatrix filter in Hybrid on the Vapoursynth --> Color --> Matrix tab in Hybrid: "From" to "Rec.709" and "To" to "Rec.601/470bg/470m". (Clear "Adjust by resolution" tick box and leave "pre and post clipping" enabled.)

Is your content properly flagged?

What I usually do to compare: load the source mp4 in VirtualDub. Go to the frame you're comparing. Video --> Copy source frame to clipboard.

Instead use vsViewer (Vapoursynth Preview) in Hybrid, there I can see under the hood.

Wild guess atm. is that it's related to Hybrid feeding ffmpeg with YUV444 data and instead of RGB data. (since y4m piping is only possible with yuv content, I assumed ffmpeg would then to the yuv->rgb conversion properly with the correct values , which is does not seem to do)
-> I'll look into it.

Cu Selur