There are two different video file formats known as Flash Video: FLV and F4V. The audio and video data within FLV files are encoded in the same manner as they are within SWF files. The F4V file format is based on the ISO base media file formatand is starting with Flash Player 9 update 3.
AOMedia Video 1 (AV1) - is an open, royalty-free high efficiency video coding format designed for video transmissions over the Internet. AV1 is more efficient than H.264, H.265, HEVC, VP8, VP9. In a comparison of AV1 against H.264 (x264) and VP9 (libvpx), AV1 showed about 45–50% bitrate savings over H.264 and about 40% over VP9 when using a constant quality encoding mode. AV1 is intended to be able to be used together with the audio format Opus in a future version of the WebM container format for HTML5 web video and WebRTC