Subtitle ffmpeg IDs have shifted in recent builds

[nissel]

I've been updating the libmpv-2.dll in my Plex HTPC install which has been working great until recently.

Something in recent builds 07/01 onwards shifted the ffmpeg subtitle index (visible in the track information stats OSD) this means the subtitle track selected in Plex HTPC no longer matches the subtitles displayed, it's off by one.

I went through the old zhongfly builds to pin point when it broke. 20260630-git-3f1b23abd0 is the last working one, and is 20260701-git-99b4c12ccc is broken.

Not sure if it's an ffmpeg change or mpv itself.

Old build working

New build not working

It might be this commit FFmpeg/FFmpeg@dbd495f

This affects all files with more than 1 subtitle track. Any idea if this is a bug or something I can fix via scripting?

[kasper93]

I don't know why the id changed, but I don't see anything on our side that we can do here. I also don't know what plex is doing, if I were to guess it maps ff-index when selecting track, so probably it would work fine if both mpv and plex uses the same ffmpeg.

I don't have plex to debug this, hopefully it's not symptom of some bigger issue.

[nissel]

I'm afraid I haven't got a window build environment set-up myself.

[kasper93]

I'm afraid I haven't got a window build environment set-up myself.

You could try this one https://github.com/kasper93/mpv/actions/runs/28984053323/artifacts/8185292870

[nissel]

That build works, the selection in Plex matches what is actually displayed again. Also FYI there is no FFmpeg Index text or number present in the OSD on that build.

[kasper93]

Thanks. Should be fixed by #18246 Some things that had expected it always may break, but there is not much we can do.

[nissel]

Can confirm the latest zhongfly build is fixed, thanks for the speedy turn around