On Thu, Jul 30, 2020 at 01:08:48AM +0200, Tobias Geerinckx-Rice via Bug reports for GNU Guix wrote:
> nginx can easily sniff iOS/Macintosh user agents and serve them an inferior
> format to match, such as h264 with MP3 audio, which can both be encoded
> using free software in Guix.

Here is where the videos are created:

https://git.savannah.gnu.org/cgit/guix/videos.git/tree/Makefile

------
$(NUMBER).clino.$(VIDEO).webm: \
	 $(VIDEO)/$(LOCALE_LANG)/durations.txt        \
	 $(VIDEO)/$(LOCALE_LANG)/audios/all.mp3	
		ffmpeg -y -f concat -vsync cfr \
		-i $(VIDEO)/$(LOCALE_LANG)/durations.txt \
		-i $(VIDEO)/$(LOCALE_LANG)/audios/all.mp3 \
		-c:a libopus -b:a 192k \
		-c:v libvpx-vp9 -crf 31 -b:v 0 -pix_fmt yuv420p \
		-af apad -shortest \
		-vf fps=25 -threads 4 $(VIDEO)/$(LOCALE_LANG)/videos/$@;
		make clean_noCli
------

So, we'd need to add a target that did "-c:a copy -c:v libx264" and add
some logic to create two videos instead of one. I didn't look into it
closely yet to see if that will be simple or not.