Inaccurate timecode - dropped/ skipped frames

[jamie-macleod]

Hi there -

I have been doing a bunch of testing and found an issue with dropped/ skipped frames making the timecode inaccurate.

Test method

1. DIY_timecode_generator (@25fps) into PC microphone input
2. Signal decoded/ displayed using TimeCode Monitor [https://timecodesync.com/monitor/]
3. Screen record TimeCode Monitor using OBS @25fps
4. Import video to Davinci Resolve and examine decoded timecode frame by frame

Problem
If you go through frame by frame, you discover that some frame numbers will be duplicated, while some will be skipped entirely. I can't seem to figure out a pattern, it seems to be random. Some seconds will be fine, others will be really bad. But I only need to record for 5-10sec to get a good selection of problems.

Results
This is a rough idea of what the timecode will look like, with the 'actual' frame count on the left vs the 'reported' frame count on the right.

( #) - TC
(01) - 1
(02) - 2
(03) - 2
(04) - 4
(05) - 5
(06) - 6
(07) - 6
(08) - 8
(09) - 9
(10) - 10
(11) - 11
(12) - 12
(13) - 13
(14) - 14
(15) - 15
(16) - 18
(17) - 18
(18) - 18
(19) - 19
(20) - 20
(21) - 21
(22) - 22
(23) - 24
(24) - 24
(25) - 1

I've checked with two separate units to rule out hardware , as well as using PCTimecode 3.0.3 as an alternative to TimeCode Monitor. I've also tried plugging into ZoomF6 and recording screen on that with similar results.

In practice, it's hard to know how much of a problem this will be. But what I will say is I had noticed various video tests being 1-2 frames out of sync from each other. I assumed this would be global offset, but if it varies clip by clip, that would make it difficult to combat in editing.

[mitkunz]

I have to do further testing and troubleshooting, but I have had not that kind of inaccuracy on my end. I will check again, but it also could be because of surrounding electronics or different/same power sources for all used devices including PC, Audio Interface etc... If that's the case, then I would suggest to try to shield the board and cables a little more or we need to come up with a ground lift solution of some kind. I'll come back to this. Thanks again for your testing and interest in the project! Appreciate it a lot!

[seeb73]

How is it with devices that record, for example, (GoPro) 23.976fps as 24fps?
Is it possible to display the time and frames on the LCD? It could also be used without sound synchronization. Connecting the GO PRO (pass-through for the microphone) costs an additional about 70 euros.