`sub-bold` not applying with `sub-ass-override=force`

mpv Information

mpv v0.39.0-706-g72d976b3c1 Copyright © 2000-2025 mpv/MPlayer/mplayer2 projects
libplacebo version: v7.349.0
FFmpeg version: 6.1.2
FFmpeg library versions:
   libavcodec      60.31.102
   libavdevice     60.3.100
   libavfilter     9.12.100
   libavformat     60.16.100
   libavutil       58.29.100
   libswresample   4.12.100
   libswscale      7.5.100

Other Information

- Linux version: Gentoo
- Kernel Version: Linux navi 6.6.67-gentoo-dist #1 SMP PREEMPT_DYNAMIC Tue Jan 14 21:57:48 EST 2025 x86_64 AMD Ryzen 5 5600 6-Core Processor AuthenticAMD GNU/Linux
- GPU Model: AMD Radeon RX 590
- Mesa/GPU Driver Version: Mesa 24.3.3
- Window Manager and Version: dwm
- Source of mpv: Installed mpv-9999 (git master branch) from system package manager
- Latest known working version: 0.38.0
- Issue started after the following happened: After updating mpv

Reproduction Steps

Set sub-bold to yes and sub-ass-override to force on a video with ASS subtitles that are not already bold in the ASS styling.

Expected Behavior

The subtitles should be forced bold.

Actual Behavior

The subtitles are not forced bold, instead matching the bold style defined in the ASS styling. Note that it does work as expected with sub-ass-override set to strip.

The inverse is NOT true however, if the subs are bold in the ASS styling, setting sub-bold to no will properly render the subtitles unbolded.

Log File

output.txt

Sample Files

clip.mkv.zip

I carefully read all instruction and confirm that I did the following:

• I tested with the latest mpv version to validate that the issue is not already fixed.
• I provided all required information including system and mpv version.
• I produced the log file with the exact same set of files, parameters, and conditions used in "Reproduction Steps", with the addition of --log-file=output.txt.
• I produced the log file while the behaviors described in "Actual Behavior" were actively observed.
• I attached the full, untruncated log file.
• I attached the backtrace in the case of a crash.

Start by reproducing the issue with the attached clip.mkv.zip using mpv v0.39.0 and the reported subtitle options, then inspect output.txt for the subtitle-rendering path. Done means sub-bold=yes is honored with sub-ass-override=force for non-bold ASS styling, while the existing strip behavior and sub-bold=no behavior remain correct.