One loop is —s, so the file is that times the loop count
and cuts on the bar. Recording plays in real time; leave the tab in front, a
background tab throttles the capture.
MP4 out, H.264 and AAC, ready to upload. Nothing is saved until you ask.
If a platform ever refuses the file, remux it — container only, picture and
sound untouched: ffmpeg -i in.mp4 -c copy -movflags +faststart out.mp4