How do you adjust sync of GPS, OBD and Video?

Oggie

I am finding that I have a synchronisation issue trying to get the video (recorded using the phones camera), the GPS and OBD channels all in sync.

Initially, the video is synchronised with the OBD (the engine sound matches the RPM gauge), but the the GPS speed info and location on the track is out. If I adjust the video to match the speed indicator and location on the map, the RPM is wrong.

Checking the data, I don't lose GPS lock at any time, though the rate does drop to a minimum of 3 Hz. It appears that GPS data lags about 5 seconds behind the OBD data. I don't see any way to get all three in sync. Am I missing something?

Phone is a Google Nexus 6P, OBD is OBDlink LX and the GPS is a DIY Bluetooth 10Hz device based on a RY725AI module.

aol_of_RaceChrono

Hi,

5 seconds delay is a lot. Sounds like a bug in your firmware or a problem with the Bluetooth. Normally even a cheapest GPS should be behind about 0.5 seconds maximum, and if it's good, one only 0.1 seconds or so. I'd do some more testing and tweaking on your GPS to reduce that delay.

Currently theres no adjustment between OBD-II and GPS data, but that's on my TODO list. Actually I have done work towards new channel filtering system just today (that will allow for example a time shift of channels).

tweej

Any update on this? I have a similar problem with loosing OBD II sync with the video in long videos.

aol_of_RaceChrono

@tweej No not really... Which GPS are you using?

ApexEight

@aol I'm having a similar issue (Google Pixel 2 XL phone, Garmin GLO, cheap Veepeak BT OBD-II module). The OBD-II data is syncing well, but I can see from the video that the lap time that's recording from the app on my phone's screen is off from the lap time on the overlaid data. Perhaps I need to update my Garmin GLO? I did notice that it appeared to drop GPS signal once during my test run. I am not using the Bluetooth GPS app.

aol_of_RaceChrono

@ApexEight are you having sync issue GPS vs. OBD-II or data vs. video? Data vs. video can be adjusted. GPS vs. OBD-II not currently, but it's on my TO-DO.

ApexEight

@aol I think my issue is sync between GPS and video because the lap timer overlay on my video is different than what my lap time is on the app. Like in this screenshot here, you can see that the overlay says my current lap time is 7.1s, but my phone shows 8.0s: https://photos.app.goo.gl/FnvdpKTMuyPQaVok7

I guess in this instance I need to move the video back .9s? How do I do that?

aol_of_RaceChrono

You can move the video similar to what you do when sync manually: https://racechrono.com/article/480

The phone screen is delayed a bit due to Bluetooth, buffering and GPS delay. So matching the screen might not give you perfect sync. Better to match map (on analysis screen), RPM vs. sound etc.