A small note on a common misconception - the mp4 format is not something that is patented - that's h264. Broadly speaking video files are first a container (e.

A small note on a common misconception - the mp4 format is not something that is patented - that's h264. Broadly speaking video files are first a container (e.g. mp4, avi, mkv, ts, etc). A container is sort of like a zip file. It groups together metadata about the file as well as the audio, video and possibly subtitle streams. In fact if you view an mp4 file at this level it reads like binary XML with 4 byte tag names. The video streams are encoded using a video codec - e.g. h264, h265 (HEVC), vp8, vp9, ProRes and many others. Audio codecs are similarly varied - e.g. AAC, mp3, vorbis, theora and others. These are the parts of the file that can be patent encumbered. In theory there is nothing stopping you from making an mp4 with vp8 video and vorbis audio. You can even ask ffmpeg to do it - it will happily oblige (and ffplay will play it). However the reality is that most non-smart video players will freak out at this kind of file. Most simple players will expect mp4 to contain h264/AAC. This reality is starting to break with h265 encoded video in an mp4 container. Hopefully some of these assumptions will disappear over time. I believe mkv is currently the only reasonably popular container format that can usually play whatever audio/video is inside (mostly because only "advanced" players can even read it). To add some confusion WebM is actually a hybrid. WebM is a more restricted mkv container with a VP8 OR VP9 video codec and vorbis or opus audio codec.