Export frame rate must match Timeline frame rate.

Batvink
Batvink Posts: 70 Just Starting Out*
edited February 2021 in Post-production techniques

This started as a question, but I worked out my problem as I wrote it. So now it's a tip, and maybe the more knowledgeable will refine it or explain what is going on.

I've read numerous posts here about out of sync video/audio when you import, but my scenario is a little different My issue is with export, not import alignment.

I have around 30 video clips, from various sources and frame rates (29.97, 30, a couple at 60). They are all from phones.

I have created a 30FPS compilation of videos, and when I export to a format like the built-in Vimeo 1080P, it's fine.

I wanted a very rough draft of the video at 12FPS, to work on the audio in Filmstro. But when I reduce the frame rate to 12, the video is a looong way out. At a guess, the video is 2.5x too slow (i.e 12/30ths). I have changed the project settings to 12FPS too (it was originally 30), but this didn't resolve the problem. I tried constant and variable bit rate on the export.

It turns out, the frame rate of the Composite shot must match the frame rate of the export settings that you use.

Without this, the audio and video don't synchronise.

Comments

  • RickBurton
    RickBurton Posts: 9 Just Starting Out*

    FWIW, I've experienced something similar when I used clips with mixed frame rate videos (18, 24, 25 and 30 FPS) and mixed audio types/rates. I wasn't exporting to 12 FPS. but 30 FPS.

    In case your solution doesn't work in the future, this is what eliminated the sync issues for me. ... run everything through Handbrake and export each clip using the same audio/video settings first, then import the Handbrake converted files to HitFilm. I was able to work all my comps and timeline at 30 FPS and I was able to export at 30 FPS without any further sync issues.

    Handbrake does have an option for 12 FPS. I'm wondering if this would have worked in your case? But for 30 clips would it also be more work than just having your comps at 12 FPS?

  • spyresca
    spyresca Posts: 261 Enthusiast

    Ensure your clips aren't using variable frame rate. If they are, transcode them to a constant frame rate.

  • Triem23
    Triem23 Posts: 20,689 Ambassador

    @Batvink as others have noted, phone/tablet/screencap video is usually VFR - variable frame rate - and should be transcoded to CFR - constant frame rate - before import.

    As you've said, in your case, that wasn't your issue. I've re-written your headline with the "solution," so future readers more clearly identify your ultimate topic. 😁👍

    Here I'll talk a bit more about what you found (it has come up on the forum before, but can be hard to find) so you and future readers understand why this happens.

    Ok, so, Hitfilm's 1-16 define absolute blocks of Video FRAMES when creating a Timeline. If you have a 30 fps Timeline that's 10 sec long you have 300 frames. Period.

    When exporting Hitfilm always uses those 300 frames, so, if you export at 60fps those 300 frames, you get a 5 second video. Export at 15 fps you get a 20 second video.

    Audio isn't measured in frames. It just plays "normal speed" and will de-synch.

    The devs have noted in the future they hope to improve how Hitfilm deals with speed ramping, which might change how Hitfilm conforms frames. In the future it might be possible to export a "draft" 15-fps version of a 30fps Timeline without changing apparent playback speed of the video, which would be nice.

  • Batvink
    Batvink Posts: 70 Just Starting Out*
    edited March 2021

    Thanks for the responses.

    @Triem23 thanks for the insights. I've often wondered why Hitfilm is not the best for speed alterations, now I can see why it's not a straightforward job to improve it.

  • Triem23
    Triem23 Posts: 20,689 Ambassador

    @Batvink yeah, I'm hoping for improvement here, but it's probably a very tricky change since the devs have to more or less change the way the whole engine conforms frames without breaking backwards compatibility.