Retiming a bake
Play a bake later or earlier, in slow motion, held, or backwards, and ramp between speeds with keyframes, all without a new bake.
A bake can play at another time and speed than it was baked: start it later, slow it down for the moment a wave crashes, freeze a frame, run it backwards. It's set in the Playback Time section of the sidebar's Display panel, changes at once, and needs no new bake.
Offset and Speed
| Setting | What it does |
|---|---|
| Offset | How many frames into the bake it shows at its start: it plays that far ahead |
| Speed | How fast it plays: 1 as baked, 0.5 slow motion, 0 holds a frame, −1 backwards |
The liquid's surface, smoke and meshes made by the bake follow, and so does motion blur.
- Start later: a negative Offset. At −20, the bake's first frame shows 20 frames late, and nothing shows before it.
- Start partway in: a positive Offset, to skip the first frames of a bake, a fountain already flowing at the start of the shot.
- Freeze: Speed 0, with Offset at the frame to hold.
- Backwards: Speed −1, with Offset at the frame to start back from.
Speed ramps
Both settings can be keyframed. Keyframe Speed 1 at frame 40, 0.2 at frame 50, and 1 again at frame 90, and the shot eases into slow motion and back. The frames played are the speed added up: ten frames at 0.5 play five of the bake.
VecFlow works the ramp out and keys it on the playback, in a node group called VecFlow Time, so a retimed bake plays the same on a computer without VecFlow: on a farm, or after Collect for Render.
Slow motion and what it shows
A bake is saved once a frame. Between frames, each particle moves on along its velocity in a straight line, and keeps turning. At normal speed that's never seen. In deep slow motion it can be:
- particles that curve or bounce within a frame move in straight steps, with a turn at each baked frame;
- smoke shows the nearest baked frame, so it steps from one to the next.
More substeps don't change this: the bake still saves once a frame. Keep the slowest part of a ramp to moments of gentle motion, or slow it less.
What goes wrong
- The bake ends early. A positive Offset or a Speed above 1 reaches the bake's end before the shot's, and past it nothing shows: bake a longer range.
- Nothing shows at the start. Offset with a negative Speed plays back before the bake's first frame.
- Slow motion looks steppy. See above: the frames aren't there to show the curve.
Related
Render Multiply
Many times the particles at render time, for the cost of a small bake: copies scattered round each particle that move with it. For sparks, dust, snow and spray.
Rendering
Rendering a bake: motion blur on particles, shapes, liquid and smoke; why Persistent Data is turned off; animation renders; and render farms with Collect for Render.