playback issues: recorded MP4 file is unscrubbable

[tfelici]

Playback using inbuilt mediamtx server (with and without &format=mp4) option, returns an unscrubbable file.
This seems to be because there is no defined moov atom in the mp4 file, which is resolved by executing the command
ffmpeg -i input.mp4 -movflags faststart -c copy output.mp4
however the mediamtx inbuilt server is unable to play this, so I need to serve this file via our own web server.
mediamtx playback should really serve scrubbable files as well as streamable, and not just something streamable