You need a suitable software like VLC to open an AV file. Note that Final Draft version 2 and later use XAV instead of AV extension for script files. An AV script consists of information such as the script's title, playwright, director, scenes, dialogues, video/audio columns, length, draft version, and character information. Final Draft, a word processor specifically designed for writing movie scripts, television episodes and stage plays, uses AV files to store movie scripts. Wireless IP cameras such as those manufactured by Yoosee and eRobot usually store videos in AV format. The video playback software shipped with the camera's DVR are usually able to play or convert AV files to MP4 or AVI. An AV file typically contains encrypted video, audio, and file metadata recorded by surveillance cameras and compressed in H264 format. AV file extension is mostly associated with the Multimedia Container Format ( MCF) used to save video files recorded by surveillance cameras and dashboard cameras. AV files mostly belong to VLC by VideoLAN.

Convert av file to mp4