After effects time warp adjust by source frame?

[cheyrn]

How do I use this? I want to change the rate at which a portion of video plays with one constraint being that a specific frame occurs at a specific time.

I have tried various combinations of setting key frames and moving the current frame. So far everything I have tried causes playback to be stuck on one frame.

I might just be confused about how to set keyframes.

If I click the stopwatch icon in effects controls, it toggles. So, how do you indicate "make a keyframe here"? If it's selected and I change the frame, I think that changes where the keyframe is.

If instead I use the diamond icon in the composition panel that lists clips, I can set and switch between keyframes, but the stopwatch remains selected and the parameter's frame number doesn't change.

If I then scrub, the composition window is frozen on that frame.

[poisondeathray]

What do you mean by "I want to change the rate at which a portion of video plays with one constraint being that a specific frame occurs at a specific time."

What does that mean ? How did you want to achieve it specifically ? slow or fast? what method? (decimation, duplication, optical flow ?)

One generic approach is to composite different layers (you have different precomps with the video at different speeds, then you add them to the main composition) . So if you need a specific frame at a specific time, put a copy of the frame where you want

The "general" way you do this with all keyframmed effects in any program is you set a keyframe to the "normal value" right before the frame of interest, then on the frame of interest you set the value you want. Same for the end of the effect, you set a keyframe marking the end, then on the next frame you set another keyframe to bring the value back to "normal" values

If I click the stopwatch icon in effects controls, it toggles. So, how do you indicate "make a keyframe here"? If it's selected and I change the frame, I think that changes where the keyframe is.

Changing the value on anyframe, when the stopwatch is activated, will automatically make a keyframe on that frame. So if you move the playhead 1 frame , change the value , it will automatically set a keyframe (it's "auto keyframing")

[cheyrn]

I want to change the rate slower or faster, and by different frame interpolation methods based on what I am trying to achieve. And these would involve using the time warp effect, specifically. Whatever method, after warping time, a specific frame in the source footage should occur at a specific offset in time.

The "general" way you do this with all keyframmed effects in any program is you set a keyframe to the "normal value" right before the frame of interest, then on the frame of interest you set the value you want.

That is probably where I am stuck. How do I set the value that I want? Here is an example:

Start of clip: frame 226
End of clip: frame 270

I want frame 270 to occur as frame 237. If I have key frames on 226 and 237, or 226 and 270, or all three, how do I specify that frame 270 occur at frame 237 after applying the timewarp effect?

Changing the value on anyframe, when the stopwatch is activated, will automatically make a keyframe on that frame. So if you move the playhead 1 frame , change the value , it will automatically set a keyframe (it's "auto keyframing")

Changing the value where?

I did this:

1. Set in/out points on footage, drag clip to composition clip list panel.
2. Select time warp effect
3. Change adjust by speed to adjust by source frame.

At that point, the composition window displays the first frame of the footage and the stopwatch is selected. If I set the frame number of the in point as the value of the source frame, it displays that frame.

Does that mean it set a key frame on the in point frame? How do I then specify another key frame? If I did mange to set another key frame, how would I indicate that it is to be time warped relative to another frame?

If I use the diamond icon, it sets key frames but the source frame parameter doesn't change.

[poisondeathray]

Does it matter to you how the transitions occur, how it ramps in speed ?

The potential problem is if you use interpolation for slow motion or speed up (or even duplicates instead of interpolation), the frame numbers change . e.g. if you slow down a clip by 50%, it will have 2x the number of frames. Your old frame number references will not be the same as the new frame references . Same with speeding up motion. You will have fewer frames

Notice timewarp is either/or for "adjust time by". You can do it by speed OR source frame, NOT both, at least not with 1 filter instance. When you use timewarp and adjust by "source frames" that just REMAPS frames. No speed changes.

So you can apply 2 instances , the first with speed change, the 2nd to remap it with "source frames" (you might have to precompose the first instance for it to work) .


Changing the value on any parameter, with the stopwatch of that parameter activated, will set a keyframe. So if you have the adjust by set to "source frame" , and on frame 1 you set it to frame 50, it will display frame 50 instead of frame 1. If you move the playhead 1 frame to frame 2, it will still display 50, because the last keyframe is set to 50. If you change the value to 36, it will display 36. Every subsequent frame will display 36, because that was the last keyframe

[poisondeathray]

It's still not completely clear to me what you are doing...

If you just want to remap frames, you can do that on the timeline by remapping frames. Perhaps this is closer to what you are trying to do ?

e.g. enable time remapping (ctrl+alt+t , with the layer selected). Normally the first and last keyframes are already set. Those mark the original clip start and end frames. Set a keyframe (push the diamond button) on whatever "specific" frames of interest that you wanted. In your example frame 270. Slide the keyframe from 270 over to 237 . The quality settings you have will determine what is being used in terms of frame blending, decimation/duplication, or pixel motion (interpolation) . Look up some tutorials on "time remapping" and after effects if you want more info

If you wanted to combine that with timewarp (the effect) , then you precompose the layer first, then do the time remapping on the timeline as desribed above

[budwzr]

Remember, retiming, velocity, playback rate, etc. affects the whole clip unless you split out the section of interest. If you push down on an inner tube in one spot, it bulges somewhere else.

You have to get a mental handle on the whole process, not just focus on keyframes. Keyframes are dynamic and subject to change if not created in the proper contexts.

[cheyrn]

I understand that retiming effects the entire clip. I'm trying to grab a spot and stretch or contract the frames around it, or before it.

I missed this part of the documentation:

Choose source frame to specify a time adjustment by identifying which source frame is to play at which time. 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, remapping a frame does something with the preceding and following frame right? This makes it seem to me like it interpolates:

http://www.danielbachler.de/retiming-with-after-effects

But, I'm not having any success. Other animation examples are changing a property value at some frame offset. Here the property value is a frame.

I tried clicking the stopwatch icon moving the playhead somewhere and setting the source frame property to some value. But, all that does is change which frame is frozen. I don't see how to create another step in the animation.

[poisondeathray]

I understand that retiming effects the entire clip. I'm trying to grab a spot and stretch or contract the frames around it, or before it.

Use the timeremap in the comp as described above. Set keyframes (not timewarp) at the points of interest, also on the ones you want kept the same. Move the points .

But, remapping a frame does something with the preceding and following frame right? This makes it seem to me like it interpolates:

Time remapping interpolates either 1) duplicates/drops, 2) blends 3) or pixel motion, depending on the quality setting switch for the layer (in a sense, all 3 could be called "interpolation" types)

I tried clicking the stopwatch icon moving the playhead somewhere and setting the source frame property to some value. But, all that does is change which frame is frozen. I don't see how to create another step in the animation.

If this refers to timewarp on "source frame" settings. I described why above. It's on the last keyframe. You would have to set a value per frame, thus a keyframe per frame

[poisondeathray]

When you have timewarp on "source frame" settings, there is no "tweening" between keyframes (tweening like in flash, or interpolation between keyframes). It's stuck on the last keyframe, or a "hold keyframe"

Most other parameters, for all effects, layers use linear interpolation by default (you can change the interpolation types, or animation curves).eg. Let's say you have 2 keyframes for a random propery like position X, the first has a value of zero at frame one , and the second a value of 100 at frame 10, frame two would automatically be linearly interpolated as "10" even though there is no keyframe set. This is also known as "tweening"

[budwzr]

Tweening and interpolation mean the same thing to me. Both have attributes that affect where frame numbers will end up differently. Like Smooth, Fast, Linear, Slow, etc.

I still don't understand the project. Are you trying to choreograph different clips to combine in an artistic way?

[cheyrn]

It's sort of stop motion animation, except instead of clay it is video clips. It's like clay that moves. I nudge the clay in different directions instead of molding it.

I figured out how adjust by source frame works. I was confused because I didn't add a keyframe at the end of the clip.

The clip is from these frames in the footage:

In: 226
Frame to move: 270
Out: 445

Enable timewarp
Select adjust by source frame
Move the playhead to 0. Click the stopwatch icon next to source frame. Type 226 in the field and press enter. It creates the first keyframe.
Move the playhead to 270. Type 246 and press enter. It creates the second keyframe.
Move the playhead to 239. Type 421 and press enter. It creates the third keyframe.

The result is that frames are interpolated between the first 2 keyframes.

Because I hadn't set the third keyframe it appeared that it was always frozen on one frame.

[poisondeathray]

I was wrong above , timewarp will actually "tween" between 2 keyframes, like any other parameter

Most people do it as time remap, because it's lower overhead (effects are more costly to render) , and there is a render hierarchy order which can be affected when you do more complex projects

[cheyrn]

It seems like I have the two values backwards. Source frame is the location the frame moves to when the playhead is on the frame to be moved.

Or, anyway, this made the first part slow:

source frame: 246 playhead 270

this made it faster:

source frame: 270 playhead 246

The thing about frames not tweening made me take a closer look and see that the frame was actually changing between the two keyframes. So, thanks that led to the solution.

[cheyrn]

Also, maybe it's not new to anyone but me. But, the composition doesn't change length when you apply timewarp. So, you have to calculate the frames (add/subtract) needed to adjust the length of the composition and change composition settings to shorten or lengthen the composition.

If you don't change the length of the composition, stretching causes the composition to be truncated and contracting causes the last frame to be duplicated to fill the composition (unless there is some other interpolation option I am not seeing).

If you have an in-point that is not at 0, when you apply timewarp initially, the frame displayed changes. It is frame 0 of the footage. This is because the source frame is the source of the transformation and it uses the start of available video to begin with. If you let if that way, frames would be interpolated such that frame zero occurs where your in-point is.

Another similarly disorienting thing for me is that to set the last keyframe (assuming you are adjusting a frame somewhere in between in and out), you move to what will be the new end of the clip, which of course doesn't look like it is the end of the clip. If you move the playhead to the out-point, that frame number is the frame number that will go into the source frame field. So, if you suffer from post-traumatic stress disorder from having made an off by one error at some point in your life, and you no longer trust your ability to add and subtract, you can get the last frame number from looking at the out-point.

If you are wanting to have a non-truncated or oddly lengthened clip, move back to the calculated end of composition frame and enter the out-point frame number as the source frame number.

Looking at the graph editor at that point finally made sense to me and displays the displacement in time.