GoPro video faster than session data

I just tried out RaceChrono a couple of weeks ago and also recorded some video on my Hero 6 Black. I signed up for the Pro trial and tried to import the video from the GoPro. I can get it synced up to the start/finish line, and fine tune it with the +/- 50ms buttons in the first couple of corners so that it matches the accel/decel curve, but by the time it gets to the end of the lap, the video is always a couple of seconds ahead of the session data recorded by RaceChrono.

I've tried both the original GoPro MP4 files and my post-processed combined video file with the same results either way. Am I doing something wrong here? The video is 1080p60 and my phone is a Pixel 1. This doesn't seem like a slow video playback issue, since the video is faster than the session data.


  • Hard to say what's wrong without seeing the raw video and the session, but I haven't seen such issue when using raw video from GoPro. You should always use the raw video, as post processing on PC/Mac might change codecs to incompatible ones.

    Easiest way is to sync according the finish line if it's visible in the map. Or maybe some other landmark visible both in the video and the map. Take a look if the video sync stays same lap-to-lap. GPS data quality might affect too, so if your data is not very good, then it will make the sync harder, and the lap timer accuracy will suffer.

    If you want me to take a look, then please share DropBox/Google Drive links to the session (.rcz share) and the raw GoPro videos linked to your session.
  • i've found the same too. originally thought it was a fixed time sync issue (say, 500 msec through entire video), but after manually syncing a gopro4 file, a lap later makes the data lag behind.
    my hardware: Gopro hero4 silver @1080/60, carista obd dongle, Garmin Glo GPS.

    files (mp4 video got another 40mins left of upload - 2.3GB):
  • edited April 2019
    @veehexx I already wrote a draft message saying that you're right the sync seems to be moving. Then I decided to re-sync it completely, from the first revs until the click of the ignition at the end, and the sync seems to be perfect throughout the video. I think it was just confusingly mis-synced, and it only made it to appear to be synced at some point.

    I will email you the "fixed" session. Try that on your phone and let me know if it fixed it for you too. If not then the video might be played back too quickly on your phone, but not on mine (Nexus 5x).

    But that said, I've seen such thing happen, that video is played back too fast. In that case the problem turned out to be that the camera created video files that played back exactly 60 fps, instead of 59.94 fps. This meant the videos were played back 0.1% faster than they should have, which meant that every minute there was 60 ms added delay. The fix was to switch the camera to 50 fps which is available on most cameras when switching from NTSC mode to PAL mode. And I need to point out that camera was not a GoPro, but some cheap random one.
  • recieved the fixed rcz in email - thanks. how do i actually import it into RCP? i've copied it to /Android/data/, and tried a refresh from within the Session section, and closing the app down but it's not appearing. I couldnt see an import option anywhere either.

    I'm using a HTC10 phone. if it is a device problem, then i'll try some other android devices and see how cope.
  • You can open it from apps, like DropBox, Google Drive or Gmail. But in theory you could extract it to /Android/data/ as it's basically zip archive of a session.

    Next version will have import functionality that you can open files directly from within RaceChrono.
  • fixed session is synced perfectly.
    was there anything obviously wrong when you looked at it, and is there anything i can do by myself to fix it?
  • edited April 2019
    The mis-sync wasn't obvious as it confused myself too. But then I decided to re-sync the videos, using the first acceleration when you enter the circuit, cannot go wrong there. Also the OBD-II data ends nicely when you switch off the car, so I used that ignition click to confirm proper sync and it was perfect. Sometimes you cannot fix it just by adjusting it, but you rather need to re-do it...
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