Use more universally-compatible pixel format for mp4 derivatives

[conorom]

Recently we uploaded a lot of videos to Fulcrum that used a pixel format incompatible with playback in Safari.

Because FFmpeg persists the input file's tracks' parameters where applicable, the transcoded mp4 (the one requested by Safari) was not playable in Safari.

This is a weird thing to track down, but seems to be a fairly well known issue. Given that the playback derivatives should be as universally-viewable as possible, it seems like the pix_fmt flag should be added in mp4 creation to ensure a user's file will produce playable derivs.

Should be a quick change to make, if others agree. Just adding -pix_fmt yuv420p there.

Links:
https://changelog.addpipe.com/fixed-rare-issue-with-recordings-not-playing-in-safari-149750
https://stackoverflow.com/a/54335942
https://superuser.com/a/1413330
https://video.stackexchange.com/a/24584
https://stackoverflow.com/questions/32829514/which-pixel-format-for-web-mp4-video
https://tools.lib.umich.edu/jira/browse/HELIO-3433

[no-reply]

this seems like a good addition.

it might be nice to make these options more readily configurable by users in general.