Cross-dissolve not working for time reversed clips, bug?

exposedpaths Website User Posts: 17 Just Starting Out*
edited September 17 in HitFilm

Hi, I'm having an issue with cross dissolving to a clip that has been Time Reversed. When I apply Time Reverse to a clip, it does not play back during the first half of the cross dissolve. Instead just a static frame is shown. Footage only starts playing after playback head reaches the start of the reversed clip.

In other words, it looks similar to a case where you try to cross dissolve to a clip that does not have any extra footage at the start: the previous clip plays ok and slowly dissolves out, while the next one dissolves in showing a single frame (=first frame of the second clip). It only starts moving half-way into dissolve effect. In this case I have a lot of extra footage around in and out points for both clips, though.

I can perhaps work around this by using two video tracks and doing separate opacity ramp down/ups to the two clips. But it is a kludgy solution.

Is this a real bug, or are there any better workarounds?

edit: found a duplicate , although I am not using composite shots, just normal timeline clips. Is the Time Reverse internally behaving as a comp shot i.e. discarding all frames around the clip thus not leaving any for the transition to work?


  • Triem23
    Triem23 Moderator Moderator, Website User, Ambassador, Imerge Beta Tester, HitFilm Beta Tester Posts: 19,935 Ambassador

    It's a bug, probably relating to order of operations.

    Time Reverse is treated as an EFFECT, which means it comes at a later point in processing the layer (to compare, other NLEs reverse clips at a point of processing before effects). I'm not sure where transitions fall in order of operations.

    Anyways, right click the time reversed clip and convert it to a Composite Shot. Move effects/masks with the clip into the new Comp

    By having the Time Reversed clip embedded in a Comp you change the order of operations. Now the Time Reverse is "baked into" the clip on the Editor Timeline. Should fix the issie.

    Note Comp Shots can be "Pre-rendered." This writes a lossless video file of the Pre-render to a folder (any changes made to the Comp after Pre-rendering invalidates/deletes the Pre-rendered video). It'll take a few moments, but, now your time reverse will be baked in and rendered to a new (temp) video file which will speed up playback on the Timeline.

  • exposedpaths
    exposedpaths Website User Posts: 17 Just Starting Out*
    edited September 17

    Right, I solved this by turning an extra-long original footage clip into a composite shot and applying time reverse there. Then I dropped comp to the timeline, decreased the duration so that it had extra frames and used slip tool to move the clip enough to have extra frames both before and the end of the timeline clip.

    I just need to keep in mind that having a time-reversed clip on the timeline and later applying transitions to it does not work. It needs to be a comp shot that has extra duration compared to what's shown the timeline.

    Perhaps there are also other effects that do this "internal conversion" of timeline clips to comp shots, I just bumped into it with Time Reverse effect.

  • Triem23
    Triem23 Moderator Moderator, Website User, Ambassador, Imerge Beta Tester, HitFilm Beta Tester Posts: 19,935 Ambassador

    Ah, yes, good on you for figuring out something I forgot to mention - needing extra frames for the transition to use.

    Hmmm. The only other effect that really NEEDS to be baked into a Comp is the SPEED effect.

    When dragging a clip to the Timeline in Hitfilm, you're creating a "datablock" with a range of frames in it. Only these frames are available. Lets assume we have a 10 sec clip (true) 30fps. 300 frames. If you use SPEED to speed up to 200% (60fps) you'll get 5 seconds of video and 5 seconds of blank. Trim the last 5 seconds? Nope. Now you have 150 frames to work with. 2.5 seconds of video, 2.5 seconds of blank. Slow to 50%? 10 seconds of slo mo video and that's it. The datablock won't extend.

    So clips using the Speed EFFECT should always be put together in a Comp for trimming on the Editor (or another Comp).

    Note this is specific to the Speed EFFECT. The Rate Stretch tool, Speed/Duration controls or editing a clip's FPS in Media Bin properties don't have the same issue, but all those other tools affect the entire clip. Only the Speed Effect allows speed "ramping." The devs know this needs to be improved, but it's difficult to change the underlying mechanism without breaking older projects, and they may be hesitant to add a 5th way of adjusting a clip's speed to the software.

    Otherwise, I can't think of other effects where order of operations requires embedding in a Comp Shot for effective operation. I do note that embedding things into Comps allows Pre-rendering, as discussed in my prior post. This is always a useful way to speed up playback shots that might use resource heavy effects filters. Fractal Noise is a good example. Fractals work on iterated equations, so, to generate a frame the noise equations are run a whole bunch of times (a parameter that can be altered in the effect). If using something like an animated 4k Fractal Noise for a texture Pre-rendering will provide a smoother edit experience than having Hitfilm calculate it on every frame.

    Final observation on Pre-renders. Hitfilm's viewer doesn't anti alias by default. Exports always anti alias, and anti alias is resource intensive. Sometimes an edit that seems fine can tip to being too much for a system to handle on Export (hint - OpenGL error messages tend to indicate overloading your system). In such a case Pre-renders of Comps reduce real time calculations and rendering to streamed video frames to reclaim resources. Pre renders are high quality lossless files (take up a lot of drive space), so they're perfectly fine to use in a final render.

  • exposedpaths
    exposedpaths Website User Posts: 17 Just Starting Out*
    edited September 17

    Thanks for the advice @Triem23. I have dabbled with temporal effects and have had difficulties with them previously, and probably forgot half the solutions already :)

    Wrt. speed effect for a comp shot - I have a time lapse that I would like to play at 75% speed and drop the rate smoothly to, say, 50% for a part of the clip. So I made a SPEED effect with keyframes changing the speed effect ...yadayada.

    I could not make this work. As soon as I dropped the initial 0.75x SPEED effect onto vid layer, my time lapse was just cut short. I was able to make the entire comp shot longer, but the actual video layer duration could not be dragged any longer. So, Comp-shot pre-render showed the first 75% of the clip playing at decreased speed, then just black. Obviously, speeding up works ok.

    Pre-renders: they tend to disappear, or otherwise hitfilm loses them when I shut down the program or it crashes for some reason. They are physically taking space on my hard disk (local hard drive, not external) and there's no reason to discard them (no media changes). But for some reason HF does not find them and show the pre-rendered icon (play icon) in the media window. This happens often enough that I do not usually spend time in pre-rendering even though they would help a lot on my computer.

    Ideally I would like to run pre-renders for H265 media that my Fuji camera outputs, right at the start of a project. But since HF anyway loses them it is sort of wasted CPU cycles.