BL Fast Start (MP4/MOV)

YouTube recommends MP4 + "moov atom at the front of the file (Fast Start)" so here's an extension for it.

"BL Fast Start (MP4/MOV)" puts a checkbox on your output panel to add a 'Fast Start' copy of MP4 or MOV renders. The checkbox shows up when you select MPEG-4 or Quicktime for the container. It will create an extra MP4/MOV file with a custom suffix (default is '-faststart'). Your normal render is untouched so you'll have two files.

In general "fast start" makes your video load a fraction of a second faster which can be handy if you're trying to make a loop with audio or trying to min/max your YouTube video performance or whatnot.

This is based on qtfaststart and was tested on Windows 11 and Linux Mint. It's all Python and should theoretically work wherever Blender works. The first thing to check if there's any problem: make sure you're on Blender 4.4+.