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Auto-detect if there’s a keyframe
Hello,
I’d like to be able to detect if there’s a keyframe on that frame or not, regardless of whether the KF’s value has changed. All the keyframes I’m looking at are hold keyframes.
There are techniques I’ve found to detect a CHANGE in the value, but I want to detect the existence of a keyframe, even if its value has not changed.
What I’m trying to achieve is musical notes automatically appearing, driven by imported MIDI data. I have a load of KFs on sliders on a null. For example, I might have a series of five keyframes, which are all value 60, and I want a series of five Middle C notes to appear.
Any suggestions would be greatly appreciated!
Not that it’s entirely relevant to the keyframe detection:
Rather than having one layer for each note, and making that layer automatically appear on cue, I’ve got one note that moves in +x (time) and moves in +/- y (pitch). I then have an adjustment layer with the Echo effect, with the echo time set to -1/25 (the comp is 25fps, so -0.04 seconds makes the echo duration = 1 frame) and the Number of Echoes set to timeToframes(time), so the number of echoes increases by 1 per frame. This makes each note ‘stick’ on screen. -
5 Replies
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Hmmmm….getting there. I found this on the AE help pages (who’d have thunk it?!):
The following expression, when written on an Opacity property with keyframes, ignores the keyframe values and uses only the placement of the keyframes in time to determine where a flash should occur: d = Math.abs(time – nearestKey(time).time); easeOut(d, 0, .1, 100, 0)
So I put that on a layer’s opacity, threw in some random keyframes, and indeed, it ignores the KF’s values and makes the opacity pulse when it encounters a keyframe. To remove the pulse, I just changed it to the following, so if there’s a KF, the opacity is 0%, and if there’s no KF, the opacity is 100%:
d = Math.abs(time - nearestKey(time).time);
d*10000 -
Continuing…
So, I added
100-thisComp.layer("note").transform.opacityto the musical note’s opacity, and it kind of worked. The only problem I now have is that the keyframes generated from the MIDI data do not fall exactly on whole frames. I increased my comp’s frame rate to 99 (the max. value), altered my Echo Time to -1/99 and it sort of works, but the echo effect is causing some weird ghosting of the notes. I suspect the notes are not on screen for long enough.Aha!
I found that the script had added two keyframes, a tiny fraction of a frame apart. Maybe it was trying to cram two notes into one slider. I changed the comp’s frame rate back to 25fps, deleted these second notes’ KFs, slid the remaining keyframes to snap to whole frames, adjusted the Echo Time back to -1/25, and lo and behold, it’s all sorted! -
I know I’m literally almost a decade late but I was trying to detect if there were keyframes and I found this thread really helpful and thought I’d add to it for anyone else looking for a solution.
For my project I wanted a property to only use an expression when there were no keyframes and then basically let the keyframes takeover when they were present.
I ended up with this:d = Math.abs(time – nearestKey(time).time);
if(d==0){
//key frame present
} else {
//no key frames
}
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Hi Steve.
I think that for an even easier and shorter code, you can go like this
if(numKeys == 0){
//no keys
}else{
//some keys
}Using numKeys also gets you the number of keys, so you can use an expression only if you have a certain number of keys.
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A nice simple expression! I find it fascinating to see old problems and solutions pop up, years later!
Ahh yes – I think I was working on an audio course for lynda.com for this and wanted a piano keyboard’s keys to flash when “pressed”.
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