Time Stretcher Node - Beginner Question

Hey guys,

I'm having a hard time wrapping my head around the Time Stretcher node. I was told it might help me carry out a speed ramp in which the clip starts at normal speed, ramps up quickly, and then returns to normal speed. I want to do it in Fusion so I can add a Vector Motion Blur node after.

Right now, I have a keyframe starting at 0, then ramping up to 100. The clip plays back between keyframe 0 and 100, but then it stops...How do I keep playing the clip at 100? Thank you.

TimeStretcher.JPG (272.05 KiB) Viewed 3061 times

What is the unit of Y axis on this graph?

What is the unit of Y axis on this graph?

Isn't it speed on the Y (in percentage) and frame number on the X?

If your clip currently doesn’t ramp up and then play at constant speed it isn’t speed graph. Another option of what it can be is source frame graph. So for each input frame, it tells which source frame to grab.

In frame graph, constant slope angle means constant speed and speed ramp will look like changing slope angle.

With a TimeStretcher, the Y axis is the source clip's frame number. That is, if at frame 120, your TimeStretcher is set to 85, you'll get whatever was at frame 85 in the node being input to the TimeStretcher.

Velocity at any given point is the slope of the line (the first derivative in Calculus terms). If you mouse over the line, the status readout will tell you the slope, which is essentially a multiplier on your framerate (in a 24 fps timeline, a slope of 2 means the footage is playing back at 48 fps).

The way I usually like to set a TimeStretcher up is to remove the default animation, then set a new keyframe at the start of the timeline matching the frame number at that point. Then set a keyframe at the end matching that frame number. In the Spline view, that will result in a graph with a slope of 1. Then I start sliding the keys or adding new ones to get the ramps that I desire. Unless you're dealing with something that can loop, leave the end-points flat to avoid the node from trying to pull frames that don't exist—it will hold frame before and after the valid footage.

If you want to ramp something up/down you can download the fuse ReTimer from Reactor. It let's you set the speed percentage on the current frame and it will give you your wanted effect with ease

In your example since you only have two keyframes, then your clip will only playback between the frame numbers entered in the keystretcher, between the positions on the timeline that you have placed them. If you only have one keyframe then whatever frame you enter in the keystrecher will display the whole length of the comp.
If your clip is 200 frames long and you want all 200 frames to play then you will need to position at least one more keyframe while entering frame 200 in the ketstretcher, somewhere else on the timeline, depending on where you want frame 200 to play.
If you would rather think in terms of speed then I think speed would be represented by, CLIP FRAMES/COMP FRAMES beteen each keyframe. So if you have a 100 frame clip and you position a keyframe for frame 0 of the clip at comp frame 0 and position a keyframe for frame 100 of the clip at comp frame 500, then you will get a clip playing at 100/500 = 0.2. Slope of the line in spline graph represents the speed, a value smaller than 1 is slower that the original clip and a value greater than 1 is faster than the original clip.
I think the method is beautifully simple compared to some software I have used.

If you want to ramp something up/down you can download the fuse ReTimer from Reactor. It let's you set the speed percentage on the current frame and it will give you your wanted effect with ease

Thank you!

With a TimeStretcher, the Y axis is the source clip's frame number. That is, if at frame 120, your TimeStretcher is set to 85, you'll get whatever was at frame 85 in the node being input to the TimeStretcher.

Velocity at any given point is the slope of the line (the first derivative in Calculus terms). If you mouse over the line, the status readout will tell you the slope, which is essentially a multiplier on your framerate (in a 24 fps timeline, a slope of 2 means the footage is playing back at 48 fps).

The way I usually like to set a TimeStretcher up is to remove the default animation, then set a new keyframe at the start of the timeline matching the frame number at that point. Then set a keyframe at the end matching that frame number. In the Spline view, that will result in a graph with a slope of 1. Then I start sliding the keys or adding new ones to get the ramps that I desire. Unless you're dealing with something that can loop, leave the end-points flat to avoid the node from trying to pull frames that don't exist—it will hold frame before and after the valid footage.

Ohhhh, this makes total sense now. Thank you.