Harry's GPS Suite Forum

Harry,

Using 20.0.11 on an iPhone 6 and iPad Air 2. I copied my 40 minute 1 lap GoPro video and linked it in HLT (there was no on board video, just the external cam). I set the sync point as I crossed the finish line near the end of the video. I have intro and extro set to 60 and 30, respectively (BTW, I wish these values could be higher, like up to 5 minutes).

While the data and video are synced at the finish line, they are not synced at the start. The start data displays about 4 seconds early. Since it is a standing start, it is pretty obvious as the speedometer is climbing and the car is not moving. Looks like the timing is about 0.2% off. If there is no way to fix this, perhaps it would be worth considering adding a sync start option along with the sync finish setting.

In v20 it is a lot easier to set the sync point, thanks! I just wish in the iPad version that the video sync screen were large. It would make navigation just that much easier.

Deven

Hi,

My guess would be you have not synced the correct lap. LapTimer uses the GPS timestamp and the frame timestamps to get the full range right if one position (end of lap) is right. Only in case the video itself has a drift in its timestamp, a 4 seconds gap can occur. But I'm not sure this is a realistic scenario for an unedited video at all... I'd suggest to go through the video using any previewer and write down the timestamps of all start / finish crossing. Calculate the (video) lap times from this. Now, compare them to LapTimer lap list to get the right lap synced to the right timestamp. This will verify there is no general drift too.

- Harry

Maybe it is because the video is edited, although nothing is changed between the start and the finish?

Am I correct in assuming that HLT cannot directly edit GoPro video that spans more than one 3.8gb file? If so, then I have to combine three GoPro files before can I send it to HLT. Having combined the files, I then apply some titles to the intro, extro, and race before I send it to HLT. Again, between ten seconds before the start and ten seconds after the finish, there is no time changes (e.g. edits, slow motion, fast motion, etc.).

The actual official lap time was 38'34.3". The HLT recorded lap time was 38'33.44". The timestamps on the processed video indicate a 38'30" lap time. I checked the raw GoPro video timestamps and they also show 38'30". So it doesn't appear that editing is the cause.

It was a standing start. My lap time started at 8:27.00 am whether I moved or not. If I left the starting line 4 seconds late, this would account for the slower video referenced lap times. But clearly I did not leave late as the official and HLT times are so close.

The timestamps in LapTimer's data recordings will be correct. They are timestamps from GPS which are powered by super precise atom clocks. In case you have no missing frames after joining the GoPro videos (or double frames), I assume the HERO has some time drift in its frame times. The only way to work around this is to pipe it through a video editor which allows this minimal stretching / compression (which means speeding up or slowing down) of timestamps. I have never done it, but it will be possible. The factor will be quite small something around 0.172%

- Harry

The frame rate for NTSC video should be 29.97fps. I don't know if that makes a difference or not, but it is 0.1% different from exactly 30.00fps.

No, that is making no difference. LapTimer reads frames and writes frames. Frame number and frame times are unchanged.

- Harry