fix mp4 on mac

Solution according to Copilot / ChatGPT for unplayable mp4 video file when ffmpeg is aborted with Ctrl+C on Mac - (for a file encoded with hvc1 codec)

ffmpeg -i gputestfixed.mp4 

  -map 0 \

  -c copy \

  -movflags +faststart \

  -tag:v hvc1 \

  qtplayable.mp4