I had this animation sequence that I wanted to slow down by stretching it out over twice as many frames, so I selected all the keys in the graph editor, pressed S for scale, restricted them to the X axis, and stretched them out to twice the length. But there are some weird glitches in the resulting render as you can see from the before and after clips below.
Does anyone know what I might have done wrong? Is there a better way to accomplish the task of lengthening a sequence?
I think the way I would start looking at this is how the animation plays in the 3d viewport after you have scaled it. Figure out which frames have the glitches, and step through the animation one frame at a time. Are all those glitches still there? I’m wondering if when you scaled things in the graph editor if all the key frames were selected. Off the top of my head, that’s the only thing I can think of…
I’ve noticed that keyed frames can ‘hide’ behind each other. I’d zoom in all the way in the animation window and look for any frame-keys that are directly next to each other, and remove them. That should fix it…
Another thing to check: In the Graph Editor/F-Curves Editor, make sure that none of the handles of your F-curves have been scraggled. By this I mean that they have been modified by the scaling so that they no longer provide a smooth curve between keyframes. Sometimes a handle can get messed up, causing a huge bump in the F-curve, and this will cause the model to glitch wildly until the next keyframe. These bumps are easily recognized because they are usually of much greater amplitude (Y-axis height) than the intended animation curves, and the handle leading into the bump is vertical or very close to it.
The fix is to select the key with the glitched handle and use Key>Handle Type>Auto Clamped (shortcut: V-KEY>AutoClamped).
Thanks for all the suggestions. I think I may have gotten myself into some trouble, though, because I decided to go ahead and finish the shorter scene with textures, world, particles, etc., intending to stretch the whole thing out again to the length I want, which means I’ll probably have a million more curves to worry about. In the back of mind, I thought I would find a more foolproof way to lengthen a sequence. Do y’all think it would be better just to render the animation with twice the number of frames per second and then slow it down in a video editor? Or should try to scale it out again and use the methods suggested here to tweak any glitches that occur?
Unless you use a video editor that can do good interpolation between frames, this will end up as less-than-best quality imo. You need to actually render more frames for your sequence to slow down smoothly, which means either scaling the f-curves or using the Time Remapping feature – this last seems to be more appropriate given that you’re working with the entire Scene, not just selected curves. But be aware that Time Remapping may result in glitches also, depending on what’s actually causing them.
If you decide to actually scale the keys and have glitches again, one way to make things easier to track them down is to run out an OpenGL animation sequence using the Stamp>Frame Number option; then you can locate the glitch-frames exactly.