The replay buffer and buckets
Turning it on
Press Add Input… and choose Replay. There is no separate switch: adding the input is what starts a continuous, rolling buffer of Program, and it keeps running for as long as the Show is open.
The buffer length
On the Replay input’s own settings, Buffer length is how much of Program is kept to capture from: 60 seconds by default, adjustable from 10 to 300. Changing it restarts the buffer, so whatever it is currently holding is lost; your saved clips are not affected.
H.264 or ProRes
The buffer is encoded in H.264 unless you choose ProRes 422 Proxy or ProRes 422 LT as its codec. ProRes is encoded separately from the stream and your recordings, so it leaves them more room, and every frame of it can start a clip, so a capture begins on exactly the frame you asked for. It takes several times the memory: the buffer holds at most 2 GB, which at 1080p50 is nearly four minutes of Proxy or about a minute and a half of LT. If that is less than the buffer length, the settings say how long it really holds. ProRes needs an M1 Pro, M1 Max or any later Mac.
Buckets
Clips are organised into buckets, named lists you set up in the replay panel, such as “Goals” or “Interviews”. There is one, called Replays, to start with. Clear Bucket… empties one without deleting it, and Delete Bucket… removes it.
Bucket names are saved with your Show. Which clips are in which bucket is saved too, alongside the clip files themselves; see playback speed and clip files for where, and what happens if a bucket has since been deleted.