WebM is an open-source, royalty-free multimedia format for streaming content online. It contains compressed video streams of either VP8 or VP9 codec and compressed audio streams of Oupus or Vorbis codec. Today, it’s one of the most widely used file formats to stream videos online because of its lightweight and real-time delivery nature.
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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