I'm trying to add subtitles for a video. Both video file and subtitles files are downloaded on iphone (*in both vtt and srt format)

Example paths:

subtitle: file:///private/var/mobile/Containers/Data/Application/384B1E38-7536-4F52-A9E1-B7D8E5A1490B/Documents/1_665ba05feee690141b7_english.vtt*).

video file: file:///private/var/mobile/Containers/Data/Application/384B1E38-7536-4F52-A9E1-B7D8E5A1490B/Library/com.apple.UserManagedAssets.q1zdd9/1_665ba05f2b5aa225440dc840690141b7_4CD8B29737842BA5.movpkg

I have absolutely no idea how i should create or prepare those files to have a AVMediaSelectionGroup and be able to select a proper AVMediaCharacteristic on

Unfortunately most of tutorials contains only examples for hls streaming, but im not sure if it is valid for offline player.

How should i use AVAssetResourceLoaderDelegate or AVAssetResourceLoader and how should i create a single AVURLAsset with all subtitles?

Could you help me somehow and describe what should i do? I am aware that the question is imprecise, but in fact i do not know where should i start (describing a path - what i should do in steps would be appreciated). Kind regards.