The short version
On YouTube, the simplest way is a Premiere: upload the video, set it as a Premiere, and viewers watch it together at the time you choose, with live chat, and no encoder running on your computer. On any platform, you can also play the file in OBS with a Media Source and stream it like any other scene. On Twitch, label that stream a Rerun: Twitch asks for it, so viewers don’t expect you to be there live.
Play the video in OBS
These are OBS Studio’s own names (version 32).
- Make a scene for the video. In Sources click +, choose Media Source, and pick the file under Local File. OBS plays .mp4, .ts, .mov, .flv, .mkv, .avi, .gif and .webm video.
- Restart playback when source becomes active is on by default: the video starts from the beginning when you switch to its scene, so switch to it when you are ready to begin.
- Show nothing when playback ends is also on by default, so the last frame doesn’t stay on screen. Add an end scene to switch to, or tick Loop to play it again.
- Tick Use hardware decoding when available to let the graphics card decode the file, when it has a decoder for that format.
- The video’s sound reaches the stream on its own, with its own meter in the Audio Mixer. To hear it yourself, open Advanced Audio Properties and set its Audio Monitoring to Monitoring Enabled.
For several videos in a row, the VLC Video source plays a playlist, with Shuffle Playlist and a playlist loop. It appears in OBS only when VLC is installed on the computer; with 64-bit OBS, install 64-bit VLC.
On Twitch: label it a Rerun
Twitch calls non-live content you play on your channel a Rerun, and asks for three things when you stream one:
- Tick the Rerun checkbox in the Edit Stream Info panel. This adds a Rerun tag and label to your channel.
- Start the stream title with “[Rerun]”.
- Start your Go Live notification with “[Rerun]”.
Twitch’s reason: without the label, viewers expect to talk to a streamer who is there, and an unlabelled rerun damages their trust.
On YouTube: a Premiere
A Premiere needs no encoder at all, and the video stays on your channel as an ordinary upload afterwards, with the chat replay.
- In YouTube Studio, click Create, then Upload videos, and pick the file.
- To premiere it as soon as it has processed, choose Save or publish, Public, then Set as instant Premiere. To choose the time, click Schedule, enter the date and time, and tick Set as Premiere.
- Under Set up Premiere, choose the countdown’s theme and length, then click Done or Schedule.
YouTube doesn’t premiere Shorts, 360° or VR180 video, or video above 1080p. Viewers can rewind during a Premiere but can’t skip ahead of what has played, and anyone who set a reminder hears about it about 30 minutes before it starts.
Questions
Premiere or a stream from OBS? A Premiere is simpler and needs nothing running on your computer, but works only on YouTube and only for the video itself. Stream from OBS when you want an overlay, a camera over the video, or a platform other than YouTube.
Does the video need special settings? In OBS the stream uses your normal output settings, whatever the file’s own: the bitrate calculator gives the numbers for your upload and platform.