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Inaccurate timecode - dropped/ skipped frames #1

@jamie-macleod

Description

@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.

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