DAT file is a file format written to save sounds, midi, wave, pallets, images, and levels. In short, this file format contains vital information for specific software, and the data is usually in either binary or plain text. In rare cases, DAT files may include a video file. DAT files are opened using text editors like Notepad++ and TextEdit.
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