MKV is a container format for holding multiple audio, video, picture, and text data such as subtitle tracks. It is similar to other common containers like MP4 and AVI, although MKV is open in the specification. For video contents, MKV uses a .mkv filename extension, .mka for audios, and .mks for subtitles.
MPC-HC, KMPlayer VLC Media Player MKV File Player MPV
AMR (Adaptive Multi-Rate Audio Codec) is a sound compression format that is designed for speech coding. It is today widely used in UMTS (Universal Mobile Telecommunication System) and GSM (Global System for Mobile Communications). Most modern mobile phones can save short sound recording clips in AMR format and can be converted to other standard sound formats using a third-party program like Wondershare UniConverter.
AMR Player Mplayer VLC Media Player QuickTime Player