AP3 file format is a VS10XX VSOS App from Asprova – an APS (Advanced Planning and Scheduling) system for Microsoft Windows OS. In short, it saves the scheduling project created via Asprova. Naturally, other apps can use files with .ap3 extensions. Just be cautious with AP3 data from unknown sources.
HEVC MKV is a digital media format that uses HEVC codec, instead of the usual H.264, which is used on typical MKV files. HEVC MKV files are encoded at lower bitrates than H.264 MKV, making them smaller by up to 50%. However, software and hardware support for HEVC MKV files is quite limited as opposed to H.264 MKV, which ranks among the most popular media formats today.
VLC Media Player
MKV File Player