A free program for Android, by UpsideDownTech.
AOne is a free video player app for Android phones. It can play all popular video formats, including MP4, MKV, AVI, MPG, MPEG, MOV, M4V, TS, etc.
You can watch videos in the background just like a music playback. You can also control volume, brightness, and playing progress by sliding on the playback screen.
The built-in equalizer can adjust the audio volume for different music genres.
Subtitles can be selected from your phone/SD card memory or you can also search and download subtitles.
You can choose between two settings. One allows you to resume all videos, and the other allows you to resume videos that are longer than 30 minutes.