Requesting filter label support with the lavfi-complex argument

Hi folks, I'm submitting a feature request for filter label support with the lavfi-complex argument.

I am creating karaoke mp4 videos for home use and I'm able to get separate backing vocals, lead vocal, and instrumental tracks using Ultimate Vocal Remover 5 and with ffmpeg, I can map those to separate tracks with an mp4 of scrolling lyrics I create using an online tool. This all works great and with guidoccella's help, I was able to play my mp4s with separate audio mapped in mpv using lavfi-complex syntax within a lua script. I'm able to by default load the three tracks no problem and have bound them to different keys in order to control the volume of each track. The problem is that when I change the volume of let's say the lead vocal track, the changes are jittery as the mp.set_property is executed for each volume change. I want the changes to occur smoothly like when using the 9 and 0 keys to change overall track volume. Anyway, I'm told that this won't happen until there is filter label support with the lavfi-complex argument.

Hopefully this can be done or if anyone else knows of a way I can accomplish this either programmatically, and/or with mapping the 3 tracks to some kind of software or hardware mixer, or whatever suggestions are out there, I'm all ears.

Thanks for your help.

The request concerns the lavfi-complex argument and its use from a Lua script, but names no source file, test, or implementation entry point. Start by locating lavfi-complex handling and reviewing how filter labels and per-track volume changes are currently exposed. Done would require agreed filter-label support that enables smooth independent track-volume changes.