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
3GP is a digital media container format developed by the Third Generation Partnership Project (3GPP). It stores both audio and video streams that are transmitted via 4G, 3G, and 2G mobiles phones. Here, the video format is saved in H.264/H.253 codec, while audio is streamed in AAC-LC, HE-AAC v1, AMR-NB, AMR-WB, AMR-WB+, or Enhanced aacPlus.
MPLayer AIMP Apple QuickTime Player VLC Media Player