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Forums Adobe After Effects Expressions Frame Advance to Beat

  • Frame Advance to Beat

  • Mark Walczak

    December 29, 2016 at 6:50 am

    Hi all,

    I have a feeling that this can be done simply with expressions, but I know there are people MUCH smarter than me here, so this is my situation:

    I’m working on a music project, and I would like to “fast-forward” the video to the beat. For instance, imagine a sequence 100 frames long. Every beat, I want to play back the first 40 frames within the span of 20 frames, and let things play at normal speed after that. The resulting clip would be 80 frames. Basically, I want a way to mathematically trigger a speed-up in time that tapers out into realtime. I’ll have to do this several times over the course of the song, so I need the ability to do this more than once.

    Please let me know if you have any questions, and thank you so much for your time!

  • Mark Walczak

    January 1, 2017 at 9:07 pm

    Just in case it helps anyone else looking for this, here’s the solution that I found:

    1 – Drag your footage into a new comp
    2 – Create an adjustment layer above your footage
    3 – Apply TimeWarp to the adjustment layer
    4 – Add a slider control to the adjustment layer
    5 – Set the TimeWarp Method to ‘Whole Frames’ and set Adjust Time By to Source Frame
    6 – Apply this expression to Source Frame: time*29.97+effect(“Slider Control”)(“Slider”)
    7 – In the above example, 29.97 was my framerate, but use whatever fps you have

    You can now simply keyframe the slider control to create your jumps in time. Personally, I set two keyframes about four frames apart. The first was linear, and the second had an ease-in applied. I simply timed the keyframes to the beat of the song, and it looks great.

    Hopefully this helps someone else!

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