If the recording was automatically split by size (e.g., 2GB chunks), ensure all sequential parts are present, as metadata may only be fully intact in the primary file. Writing an MP4 Muxer for Fun and Profit - OBS Studio

It may be a Hybrid MP4, which combines fragmented writing (to prevent corruption during crashes) with a "soft-remux" to ensure compatibility with standard video players.

The file is composed of "atoms" or boxes, including: ftyp: Identifies the file type and compatibility version. mdat: Contains the actual media data (video/audio).