iOS Video Export — Huge files with wrong framerate

Hello everyone,

I have a constant and very inconvenient issue in RaceChrono iOS overlaid video export. Whenever I do that, I end up getting huge files (~1GB per minute), which have corrupted framerate (660 FPS), and therefore wrong video duration with slowmo taking most of the video.

iOS usually can't open those files at all, and MacOS' QuickTime shows slow-motion segment for the bigger part of the video.

The only cure is to open the video in iMovie, remove speed adjustments and re-export, which results in 10x smaller file with same quality.

Source video is GoPro 1080p/50fps, added and manually synced with a session. Reproduced every time on iOS 14, iPhone 8 Plus.

Also, video quality settings on iOS don't seem to make any difference whatsoever, neither on the bug nor on the output file size/quality.


  • edited July 2021
    The quality setting is a known bug :)

    Never had problems with GoPro files before, did you possibly use a video editor on it first? Or did you upload it to your phone through the Photos app, and maybe did some adjustments there?

    1) Please share the session as .RCZ file and email to me

    2) Please upload the source video file(s) to Google Drive or similar and email the link to me (such that anyone can access with the link). It's important that you share the exact same file you linked to your RaceChrono session.

    If you do not have my direct email, please use tracks(at)

  • Huh. I've ran some tests and I think have found the culprit — you were right about the editor, I completely forgot about that.

    Turns out there is no problem when attaching raw GoPro videos (GoPro>Mac>Airdrop to phone>Add to album).

    However the problem seems to reproduce when I trim the video file with Quicktime, and then export in H.264 (file becomes a .mov), before uploading it to the phone, to simplify the syncing.

    I've sent the source and resulting files to you to take a look.
  • OK. Thank you for the samples.

    Probably RaceChrono or iOS recognises the source video frame rate wrongly. I will create TO-DO for this, and will fix it when I have more time, and it is easy enough. It does not seem very urgent, as there was a video editor involved.
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