Build with another version of mpv instead of the builtin mpv?

[Kabouik]

Describe the bug
Since Stremio 4.0, Stremio comes with its own builtin version of libmpv. This prevents using a custom built version of mpv, for instance to allow extra ffmpeg audio filters or video interpolation with vapoursynth.

This was possible in the past: one could just edit /opt/stremio/server.js to edit the path to the mpv binary, and then write-protect server.js to prevent it from auto-updating. This allowed me to use libmysofa and 60 FPS interpolation with Stremio when opening the streamed file in mpv, which was really awesome.

It does not work anymore with later Stremio versions, probably due to the inclusion of the builtin libmpv. I can no longer enforce Stremio to use a different mpv binary. Even when stremio.js is edited accordingly, whenever I launch Stremio from terminal, I can see that it is using another mpv version built at an "UNKNOWN" date, and it is not /usr/bin/mpv nor /usr/local/bin/mpv.

The inability to use custom mpv version with its own mpv.conf and additional libraries is a major regression, it defeats the point of the whole external player feature. I reported the issue months ago on the Stremio subreddit but didn't get any answer, so I am wondering if you would know if it can be modified when compiling using your scripts?

To Reproduce
Steps to reproduce the behavior:

1. Start streaming a file
2. Open it in mpv as external player
3. Alternatively, alter stremio.js to use the path to another version of mpv (for instance, mpv-git built from the the mpv-git repository)
4. See Stremio either failing to open mpv or using its builtin version

Expected behavior
Stremio should be able to use a real external player, not a builtin external player that cannot be customized or even configured with mpv.conf.

Please include the following:

• Solus 4.1
• Mater branch, but I am not reporting a Stremiio-Install-Scripts bug, rather asking if this can be enhanced to support custom mpv installations