An Open Source PSVita/TV MP4 player with 1080p playback and subtitle support
1080i output supported on the PSTV natively and on the Vita with Sharpscale
MKVs do NOT work. If you want to preserve subtitles with MKVs I recommend using Handbrake to convert them to MP4 with Timed Text Subtitles. Direct FFMPEG will also work.
Note to Devs
SceAvPlayer does not support 1080p video playback by default. You need to patch the module in order to do so. That's what ReAvPlayer is for.