give an option to improve performance on low-powered devices

[jose1711]

i suggest here to add new command line switches to be able to set both mpv_version and mpv_options manually (by user). the reason would be that runnig mpv --version and especially mpv --list-options substantially contribute to the total startup time.

some stats from my raspberry pi zero. startup time measure using time echo q | mpsyt

stock 0.2.7.1:
32--39 seconds

hardcoded mpv_version and mpv_options (removing function calls):
18--23 seconds

i am not suggesting to remove the detection, only adding an option to disable (somewhat expensive) detection should a user provide this information beforehand.

[ids1024]

Interesting; I wouldn't really expect this to take very long. This is a sort of awkward thing to add, but I can't think of a better way, unless mpv is doing something silly that can be fixed there.

Loading youtube_dl is probably also a noticeable contributor to startup time; I know they added some experimental code to help with that (ytdl-org/youtube-dl#8497) but I'm not sure what the current status is.

[jose1711]

it was a bit of a surprise to me as well. mpv --version alone takes 7--8 seconds, mpv --list-options roughly the same. 14-15 seconds difference is confirmed by the previous "benchmark".

i admit the proposal is more of a workaround to an unbearably slow startup time of mpv. by looking at strace output it's opening 270 files (audio libraries, samba, etc) so i am a bit skeptical when/if mpv maintainers fix it. also note that mpv --version also reports ffmpeg libraries versions (which are somewhat useless for mpv if i understand it correctly). maybe this contribute to the startup time as well.

was experimenting with slimming down of youtube_dl extractors but in the end i gave up so thank you for the link, will check it as well.