Perhaps you could try to embed the subtitles within the file, speaking for MKV-format. For this I'd recommend Handbrake for transcoding the AVI-files into MKV and MKVToolNix-Gui for doing the final work. I have therefore no further problem to display subtitles on this way!
Human being in favor with clear principles and so also for freedom in soft- and hardware!
Certainly anyone who has the power to make you believe absurdities has the power to make you commit injustices: For a life of every being full with peace and kindness, including diversity and freedom. Capitalism is destroying our minds, the planet itself and the universe in the end!