Why is it impossible to trim a reversed video?

assen Posts: 17 Just Starting Out*

I want to make a "boomerang" type video. I put a trimmed clip on the timeline, duplicate it and reverse it. Then I want to find the best moment between the two videos so that the reversal is not annoying. I try to do it with Roll Edit Tooll and the result is not a result. It's impossible. This is very easy with other, even free editors, but I want to work with one, not switch between several to perform a simple operation.


  • Triem23
    Triem23 Posts: 20,298 Power User

    Here's the short answer that gets you editing what you want to edit.

    Convert the reversed clip into a Composite Shot THEN trim it in the Editor.

    If you really really want the "why," it all comes down to order of operations. Now, a month ago you asked about slow motion and I wrote.

    "The issue here is the initial design of Hitfilm conforms frames when clips are dropped on the and that's a very difficult behavior to change without breaking backwards compatibility with old projects."

    And we need to talk about that more.

    As soon as you drop a clip onto a Hitfilm Timeline a "datablock" is created that holds those frames. Let's say you have a 30 second clip at 30 frames (true) per second. 900 frames. Computers start counting at 0 so these frames are frames 0 to 899.

    Ok, so let's say you only want the middle 10 seconds so you add those to your Timeline. You are using frames 299 to 599 of your footage.

    This happens FIRST. And happening FIRST is important. The frames used in the clip are "assigned" BEFORE EFFECTS are added.

    Time Reverse is an EFFECT.

    If you change the frames in a datablock with the Roll Tool or by trimming you've changed the frame range in the block before its reversed.

    So we are using frames 299 to 599...this is set before Time Reverse, which is an effect... So you trim off the first 30 frames of the datablock. Well, you just changed your datablock to frames 329 to 599...THEN the Time Reverse happens.

    It's basically the same thing with the Roll Edit. It's defining frames in the datablock before the Time Reverse is applied.

    Converting the Time Reversed clip into a Composite Shot "bakes in" the reversal effect, which will let you trim the reversed footage correctly in the Editor.

    Now, "conforming frames" has another thing you need to understand. When you drop the footage on the Timeline, not only are you defining frames, but those frames are matched to the Timeline by duplicating or skipping frames. Let's say we've got a 30 second clip at (true) 60fps being edited on a (true) 30 fps Timeline. Once again, we want the center 10 seconds. This is the frame range 598 to 1198 - but only the "even numbered frames." In placing the 60fps footage on a 30 fps Timeline Hitfilm immediately "throws away" half of the frames.

    These are important to grasp because the same order of operations affects every effect in the Temporal Effects group, including the Speed effect for speed ramps. It's annoying, it's unintuitive, and it makes dealing with Speed ramps and time reversal effects in Hitfilm annoying to set up, but, since this is related to entire core order of operations in Hitfilm, you should now understand why its nearly impossible to fix without breaking backwards compatibility with older projects/versions.

  • assen
    assen Posts: 17 Just Starting Out*

    Thanks for the comprehensive explanation. It explains the problem very well, but does not provide a solution to it. :)

    Converting the Time Reversed clip into a Composite Shot "bakes in" the reversal effect, which will let you trim the reversed footage correctly in the Editor.

    I tried this from the beginning. It does not work. Obviously I will have to act the hard way. Reverse, export to video, re-import.

    These are minor issues, but unfortunately they spoil the pleasure of working with Hitfilm.

  • DavidLamarre
    DavidLamarre Posts: 75 Enthusiast


    Now I get it! Thank you for this explanation!

  • premiere_studios
    premiere_studios Posts: 131 Enthusiast


    You may be misunderstanding @Triem23, you put the time reverse effect on the footage, THEN put it into a composite shot, so the time reverse effect is in the baked-in comp. now edit on the EDITOR and it will work.