I think you are using time remapping. If so you will see two keyframes when you enable the effect. The first is the starting frame, the last is the ending frame. You can pick any point in your timeline to set a new keyframe. Nothing changes until you move that keyframe. For example, set a keyframe at 2 seconds then move it to 1 second. The 2 second part of the shot now occurs at 1 second so the first second plays at double speed, then the rest of the shot plays slower. If you copy the keyframe now at 1 second and paste it at 2 seconds then your video will play at double speed for the first second, then freeze until 2 seconds, then resume playing normally....
I figured out how it works. I was confused because the frame is frozen on the keyframe and I hadn't added a keyframe at the end.
Source frame appears to mean the frame that is going to be remapped. For example, if frame the clips will be stretched so that frame 10 appears where frame 12 was, frame 10 is the source frame.
I did this:
Enable timewarp and adjust by source frame
Move to frame 0. enable animation. type the in-point frame number from the footage and press enter.
Move to the frame that is the target of the move. Type the number of the frame that will be moved, and press enter.
Move to the out-point of the clip. Type the frame number that matches the end of the clip moved by the number of frames the 2nd keyframe was adjusted by and press enter. For example, the clip was 100 frames long and frame 10 was moved to frame 12, the end of the clip would be frame 101. In the other direction, moving from 12 to 10, the end of the clip would be 97.
The frames preceding the source frame are stretched and contracted. The frames after the source frame move uniformly without stretching or contracting. It's like moving curtains on a curtain rod, rather than tugging on the middle of a rubber band.
Thanks. But, I am asking about time warp.
This seems close to giving the answer, because it at least uses source frames:
But, it involves changing fps. So, I am not able to think of how that would work for me, at the moment.
There are these things:
Frame to move 270
Frame at current desired position 247
Frame at start of selection 226
Maybe some of these are where you set a keyframe:
Keyframe at start
Keyframe at desired position
Keyframe at current position
When I select a clip to add to the composition and then select time warp from effects and select "Adjust time by source frame", the composition panel displays the first frame of the original footage.
The after effects help says that you can click the stopwatch to set a keyframe at "the current time" for that property value. Which current time?
If I click the stopwatch icon in effects controls for the source frame property, it stays selected. How do I indicate that I now want to go to a different location and set a keyframe?
If I knew how to set the keyframes, how would I tell it to now apply the time warp effect?
If I use the animation menu instead, there is an option to set a keyframe at the current source frame. Selecting that toggles the stopwatch icon, leaving me with the same questions.
If I click the triangle next to timewarp field in the composition window that lists clips, I can get at a diamond shaped icon to set key frames. I think I have set 3 keyframes at start, desired position for the end and the current position of the frame I want to occur at that position. Meanwhile the source frame property still says 226. If I scrub the composition windows displays that frame only...
I have no clue what I am supposed to do.
I missed this part of the documentation:
If you choose Source Frame for Adjust Time By, then you must animate the Source Frame property to do anything other than freeze on one frame.
But, so far, I haven't figured out how you animate the source frame. Whatever value I put in it is the frame that is frozen. I don't see how to then add another step in the animation.
I have the 2nd step backward. And the clip doesn't change length like I thought it does.
The source frame appears to be the frame that will be moved. Frames before the source frame expand or contract. Frames after the source frame move uniformly without expanding or contracting. But the composition length stays the same.
So, if you move the source frame ahead in time, the end of the clip becomes truncated.
If you move the source frame backward in time, the last frame of the end of the clip is duplicated to fill the length of the composition.
The various tutorial videos I watched all explained that but it didn't register in my mind.
Once things appeared to be working, looking at the graph editor helped me understand what was going on.
If your in-point is not 0, when you first enable timewarp, the composition window shows frame 0, while your composition frame number is still the in-point frame relative to the footage. This shows that the source frame is the frame that is going to be moved to where the playhead is.
This is what I did:
Set in-point and out-point in footage and create a composition.
Lengthen or shorten the composition in proportion with where you are moving the source frame. You can do that before or after setting key frames,
As an example, this is what I did to adjust one point in the clip contracting and shortening the composition:
Set in-point to 219 and out-point to 338
Create a composition from the selection.
Change composition settings so that the length is changed from 120 to 90.
With the play head at 219, enable timewarp
Expand the effect field in the composition panel. Expand timewarp.
Set adjust time by source frame
Enable animation (click the stopwatch). A key frame is created.
In the source frame field, type 219 and press enter.
Move the playhead to 240
Click the diamond icon in the source frame row to create the middle key frame.
Type 270 in the source frame field and press enter.
Move the playhead to 308
Set a key frame and enter 338 as the source frame
At this point the out-point is still 338. So, if you forget how to add or subtract you can can go to the out-point to find the source frame number.
The composition has now been warped.