It may just be me, but these videos never play for me.
I downloaded it and can watch it now, and suddenly the file is now visible in the web page. Are you making these videos fast start so we don't have to download the whole thing before it starts, that puts the headers in the front so the web browser can see it fast.
ffmpeg -i input_video.mp4 -c copy -movflags +faststart streamable_output.mp4