Subtitles problem ipad

Hello, when using ipad with airvideo, I cannot have subtitles (polish) in neither .srt nor .txt format. Only automatic choice appears when subtitles menu is chosen and no other possibility is active. Please help me solve this

What is the subtitle file name? It has to be exact same as video file with srt extension (not txt), assuming it is a valid srt file.

Thank you. It worked. Last question: only .srt subtitles can be used?

srt, sub (microdvd format, not sub/idx), ssa/ass and smi formats are supported.

Thank you for your helpful guidance