In Chromium test data, files are used to test video playback and processing capabilities.

These are often used as inputs for ffmpeg tests to test fragmentation ( _frag.mp4 ), track mapping, and audio-only scenarios. 4. Characteristics of the MP4 Format

They act as a "wrapper" for video, audio, and subtitle data.

In the context of the GitHub issue 2172, refers to a video file that is being analyzed by a machine learning tool, specifically DeepLabCut .

They generally offer high compression with a good balance between file size and quality.

in this case, v. mp4 is the video it just analysed and is trying to analyse again and failing with this error. Video shooters.... MP4 or MOV files... and why? - Facebook