[RFC] player/command: reinit video chain when decoder thread count changes

[christoph-heinrich]

My goal is to reinitialize the video decoder when the vd-lavc-threads option changes.
This reinitializes the whole video chain, no idea how this could be restricted to the decoder only without touching the rest of the chain or if that's even desirable.

I don't really know what I'm doing here, so there is probably a much better way to achieve this.

We could also extend this to other decoder related options once the approach has been figured out.

[kasper93]

This is hidden as private for a reason. You can add a function that acts if any of the setting has changed. And check in command.c opt_ptr == &opts->vd_lavc_params only. EDIT: this will not work, but something like that has to be done. (just implement the check in vd_lavc.c

This is hidden to avoid leaking implementation details over other modules.

[christoph-heinrich]

So instead of the struct the header defines a function that takes the pointer and context and then does the if from command.c in there?

[kasper93]

function also doesn't fit into the design looking at it.

If fact common way is to use flag like flags & UPDATE_VD and reinit then. Mark option with this flag.

[christoph-heinrich]

That's much better, thanks.

It looks to me that we could rename UPDATE_HWDEC to UPDATE_VD and do the same thing for any of those options instead of only the hwdec one.
Doing that required changing the absolute seek to a relative one, otherwise it wouldn't work well with vd-queue (starting a video would offset the starting position by vd-queue-secs seconds).

I've pushed that change and it seems to work fine for hw and sw decoding, but I didn't try all related options.

[github-actions]

Download the artifacts for this pull request:

Windows

• mpv-i686-w64-mingw32
• mpv-x86_64-w64-mingw32
• mpv-x86_64-windows-msvc

macOS

• mpv-macos-14-arm
• mpv-macos-13-intel
• mpv-macos-12-intel

[christoph-heinrich]

Using this with a conditional auto profile

[auto-vp9-vd-threads]
profile-cond=get('current-tracks/video/codec') == 'vp9'
profile-restore=copy
vd-lavc-threads=12

leads to those errors repeated a bunch of times for local files (not for networks streams)

[ffmpeg/video] vp9: Not all references are available
Error while decoding frame!

Everything works fine, but that's not great.