The stock Android TV system does not come with a video player, some vendors may include one, for example, Nvidia Shield, however the player may not have too many features, in fact, the most important and the basic one, subtitle displaying, is often missing.
Subtitle: SRT, SSA, ASS extensions
When we download a video file, it often comes with another file in .srt, .ssa or .ass extension and what is it? It is actually a formatted text file, if you open it with a text viewer you will immediatelly find out that there are timeline information and subtitle text in the file. You may also want to check the encoding of these files, you should use UTF-8 nowadays since it supports multiple languages.
Some people may also want to show 2 subtitles at the same time for language learning purpose, the Video Player for Android TV can do this.
Files in MKV/MP4/M2TS/AVI extensions are video files, it is a volume of multiple video and audio tracks, it is possible to store multiple audio tracks in one video file so you can possibly select which audio track to use when playing back this video.
How to play video files with subtitle on Android TV or Mi Box
Today we are gonna show you how to play MKV/MP4/M2TS/AVI video files with subtitle files on Android TV Mi box s systems such as Mi Box, Nvidia Shield and Amazon Fire TV. Now please watch this tutorial video
Video Player for Android TV Google Play Store link