The session was already being recorded.
The whiteboard writes a new version of the board every time it saves. So a channel that has been drawn on is a recording, and always was — nobody had built the thing that watches it. Open the same channel here and scrub back through it.
What it demonstrates
The channel as an ordered log. Every other app on this site treats storage as somewhere to
keep the current value; this one treats the list of versions as a timeline, which is what
storageAdd is actually for. Each version is encrypted with the channel
password, so Rewind can only replay a session you already had the key to.
How it draws
From the stored strokes rather than a picture: each save carries the paths that made the board, so a session replays at whatever size the window happens to be. Boards saved before strokes were stored as objects fall back to the image in the same record, which is why an old channel still plays.
Read-only, deliberately
A player that could write would have to agree with whoever is drawing right now about what the board is — and settling that argument is exactly what host authority is for. A viewer does not need to join it, so Rewind never sends anything at all.