A video or GIF won't play

Watching

Tap the video: videos in the feed don't start on their own, to save data; tap the cover to play. They pause when you scroll away or switch tabs.
"Couldn't play the video": check your connection and try again. Once a video has fully downloaded, it doesn't use data again.
GIFs don't move: make sure the app is up to date. In older versions, GIFs could freeze on the first frame when "remove animations" or power saving was on.
No sound: check the sound button in the player and your phone's media volume. Short GIF clips are silent by design.

A post video can be up to 2 minutes; longer videos aren't trimmed, they're rejected.
Very large videos can't be uploaded; try a shorter one.
Daily video limit: 2 video posts a day on Free, 10 on any paid plan. Short GIF clips don't count.
A GIF file can be up to 8 MB. "GIFs" saved from your keyboard or WhatsApp are really short videos; these can be up to 20 seconds and 12 MB.
Don't leave the app while a video uploads; the post is shared when it finishes. If the video can't be uploaded, the post isn't created and your text is kept.

On a slow connection, switching to Wi-Fi speeds up both uploading and watching.