Manual search for subtitles by text about iina

[low-batt]

I've labeled this as a feature request for the ability to override the search string when searching for subtitles.

Note that when streaming from a URL, IINA will only use the URL as the search string if the title of the video is not available. Playing the following video:
https://www.youtube.com/watch?v=tO01J-M3g0U

The log file shows IINA was able to obtain the title from YouTube and used that when searching for subtitles:

21:36:07.827 [opensub][d] Searching for subtitles of movies matching 'The World in HDR in 4K (ULTRA HD)'

The mpv log shows the property IINA reads to obtain the title being initialized:

[  39.952][v][cplayer] Set property: file-local-options/force-media-title="The World in HDR in 4K (ULTRA HD)" -> 1

[rasitayaz]

I agree that this would be a very useful feature. Additionally, IINA should prefer metadata information over the filename if/when available.