There are two built-in ways to watch something together on Discord: stream your screen to a voice channel with Go Live, or start the Watch Together activity, which plays YouTube videos for everyone. For a film you have as a file, a third way gives everyone full quality: each person plays their own copy in sync here, while Discord carries the voice chat.
Screen sharing is the quickest to start, but every viewer sees your stream after it has been compressed and sent through your upload, at the resolution your Discord plan allows. When the film matters, or your upload is slow, it’s worth the few minutes it takes to get the file to everyone first.
This guide covers all three. The third uses the sync player with the invite front and centre, the same set-up as a watch party without Discord.