Display cached in OSD seekbar, like in OSC

mpv version and platform

mpv 0.30.0-133-g35de8ea0a8 Copyright © 2000-2019 mpv/MPlayer/mplayer2 projects
 built on Sun Nov 10 18:36:28 +08 2019
ffmpeg library versions:
   libavutil       56.35.101
   libavcodec      58.60.100
   libavformat     58.34.101
   libswscale      5.6.100
   libavfilter     7.66.100
   libswresample   3.6.100
ffmpeg version: git-2019-11-09-0f89a229

Windows 10 x64 1909

Reproduction steps

In input.conf I have the following set:

RIGHT		osd-msg-bar seek  10 relative+exact
LEFT		osd-msg-bar seek -10 relative+exact

Which displays duration in text and the seekbar at the same time.

In the OSC, a visual representation of the cached content is added with a line across the seekbar.

Desired behavior

Display the visual representation of cached content in the seekbar on OSD as well, like OSC.

This is without a doubt a very specific "comfort" use scenario. The reason I ask for this is that, for comfort sake, it would be great to see cached content while using input shortcuts instead of having to keep showing the entire OSC.

P.S.
Apologies for the potato quality in screenshots, testing my script with ytdl.

Thanks so much for the awesome work on mpv, guys. Genuinely appreciated.

Start by comparing the OSC seekbar's cached-content rendering with the OSD seekbar used by the osd-msg-bar commands in input.conf. Trace how each seekbar is drawn and identify the OSD entry point that would need to expose the same cache indicator. Done means the OSD seekbar visibly represents cached content while seeking, without requiring the full OSC.