Add the options/commands to fix/adjust brightness independently for subtitles

[hooke007]

Expected behavior of the wanted feature

As the title suggests. The typical use case is for subtitles with hdr videos. A subtitle with low-and-fixed brightness is good for uesrs' eyes...

Alternative behavior of the wanted feature

n/a

[carycary246]

Would very much like this feature to be added. Also some additional suggestions - in an older version of mpv (0.35.1) HDR inverse tonemapping would also apply to subtitles but that is no longer the case with latest builds (unsure when this changed sometime last year). This results in situations where subtitle masking over signs would no longer match the video colors due to difference in brightness/tonemapping. If this can be configurable, or only applicable to signs that would be the best use case. Screenshot showing old mpv behavior vs current.

Regarding general brightness for subtitles in HDR videos, the current situation is not great and more configurability would be much appreciated. Currently the workaround is to use a gray subtitle color override as pure white is much too bright in HDR. However, in very low APL scenes, even a gray subtitle color may still be brighter than the scene which will ruin the image contrast. On the reverse side, when the scene is high APL, the gray subtitle will be hard to see. Perhaps a solution is to have a dynamic and/or configurable minimum subtitle brightness and maximum subtitle brightness based on scene APL detection.

[cest-la-v]

For text-based subtitles, mine works fine, not sure if it's the color.

 sub-blur = 1
 sub-color = "#FFD766"

For image-based subtitles, it's blinding bright even with darker color like red.

I tried the same video with potplayer. Not sure if the diff can be see from these previews.

MPV Potplayer