What pictures and videos can a post have?

A post takes up to 10 files: JPEG, PNG, GIF or WebP pictures up to 8 MB, and MP4 or MOV videos up to 9 MB. Drag them onto the composer or choose them.

Each network takes less than that in places. Instagram takes JPEG pictures only and always needs a picture or a video. The composer tells you before you schedule. An upload that isn't saved on a post is deleted after a day.