DF Time Stretch

Jace_FX Tutorials

Digital Fusion 3.02 Time Stretching Tutorial

The time stretcher works such that as you place a key frame in "current" time showing a value of "clip" time. For instance, if you wanted to take a 100 frame sequence and make it run at 4x speed, you set keys at 0 with a clip time of 0. Next set a key at current time of 25, with a value of 100. In the following tutorial, I'll attempt to explain how to do this basic time stretching and then extrapolate to a more advanced vari-speed.

Basic Time Stretching;

In Digital Fusion 3.02, start with the following;

1) Add a loader with appropriate footage.

2) Look at your footage using the transport controls. Drag your loader up to the large view so you can see it. Click your loader, and this should provide the transport controls at the bottom of the tool rollout area. My sequence is from 0-52. Take this time to decide on what frames you want where. *Note; if you use the trim tools under the loader they will effect your timescale tool, but will not effect the scrubbing of the transport controls.

3) Add a [TmS] (time stretcher) tool. This tool has a bezier spline automatically added to the source time screw (in the tool rollout).

4) Using the time slider at the bottom of the screen, make sure you are at frame 0 in current time. Next adjust your time stretcher source screw to 0.

5) To speed up the clip we need to do some math. Since my clip is 53 frames (0-52) and I want to double it's length, I take 53x2=106. So I move the current time slider (at the bottom of fusion) to frame 105. Then I set the time source screw to 52. This should double print each frame (provided the interpolate frames is unchecked in the time stretcher tool) to get the slow mo-effect. You can test this by dragging your current time slider back to 0, and then hitting the "]" and "[" keys to advance or retreat one frame at a time. You can also check your spline in the spline editor by hitting the spline tab, or hitting the "F8" key. It should look similar to image 2.

6) Next check the interpolate between frames under the time stretcher tool. Again, go to frame 0, and advance 1 frame at a time. You should now see a small amount of blending between frames. The sample spread governs how much of the frames before/after the current clip time are blended into the frame. A value of .25 takes 25% of the frames before and after and 50% of the current frame. This should be the maximum for the tool under generic uses.

Intermediate Time Stretching;

That was nice wasn't it? That basic function can also be accomplished with a time speed tool, but I'll get into that later. The power of the time stretcher comes if we want our clip to run at 1x for 1/2 of the clip, and then slow to 1/2x??? Well I'll show you how.

1) Start with the basic flow of your loader, and a time stretcher.

2) We start again with setting a key of our clip time at 0. Set your current time to 0, and adjust your time stretcher source screw to 0.

3) Time for some math again... my clip is 53 frames, and I want it to run 1/2 its length at 1x speed. So 1/2 of 53 is 26 (give or take). I set the current time slider to 25. (Again, 0 counts as a frame.) Set the clip source time to 25 also.

4) So now that we have the 1st half of the clip set, we need to do some more math. If half of our clip is 26 frames, and we want it to play at 1/2x speed, that would be 53 frames. But we need to add the first 26 frames of our clip as well. So, our next key frame would be at 53+26=79. Scrub to current time 78, and set your source time screw to 52. (The end of the clip.) Open the spline editor and look to see if your spline looks similar to mine. I've stretched the scale up so you can see the spline effect more clearly. As you can see this causes a "crash" of the time stretching at frame 25. Let's add a 10 frame transition zone.

5) Set your current time slider to 35, and look at your source time screw value. This is important for the next step. Mine is 30. I add an extra key at this point with the current value of 30. You can do this by clicking on the spline in the spline editor, and then keeping an eye on the two values in the top of the window. Alternatively, you can just click, and then set your values in the top of the window. See image 4

6) Now here's where it gets a bit tricky. First we need to find the median value of where 1x and 1/2 times would be. Obviously 30 & 35. So a difference of 5, and then 1/2 of that equals 2.5. We add that back to the original 30, and get 32.5. Now to illustrate why we do this. If we just select the 2 keys at frames 25, and 35, and hit the "s" to smooth the keys, (alternatively, we can hit "l" to make the keys linier,) we get an odd hump, and not a smooth transition. If we adjust the second key (at frm 35) to our new value of 32.5, and re-smooth the keys, we get a much more natural transition. We've just eased into our transition going from 1x to 2x. Now this may not be that noticeable at 1/2x, but if we were going to 1/10, the transition would be much more noticeable (in a good way). But we aren't quite done yet.

7) Now we need to adjust our out point. Our original calculation was the difference between 30 & 35. (35 at 1x, and 30 at 1/2x) So we subtract 5 from the end key. We can check this by scrubbing thru the rest of our spline, and checking to see that the values in the source value screw are "even" numbers. I.e. 30.0, 30.25, 30.5, 30.75, etc.

Keep an eye out for an advanced Time Stretching Tutorial and others later.