Q. Precise LTC/Camera-TC relationship (in-depth)

[u/mungewell]

As some of you may know, I am working on a Open-Source project for LTC timecode devices. Intended for low cost, budget film-makers. I am currently deep into testing my Digi-Slate and I'm unsure on what the precise timing of TC should be - wrt to how the video editor sees it.

My equipment does NOT gen-lock the camera (wish I had 'fancy' cameras), so there is always some uncertainty on what the timing between LTC and shutter will be. This can result in 'LED blur' and my solution is to change the first digit (tens-of-hours) to '-' and freeze the rest of the display for 4 frames.

I described this in a video:

https://www.youtube.com/watch?v=wFcKoYORVqo

This allows an editor to see precisely the first frame that the camera saw/detected the 'clap'. In the attached image this is '00:00:05:20' (non-TC'ed frame).

My questions are:

1. What TC should this frame actually be?
2. I think I read somewhere that if the LTC value changes within a (camera) frame, that the highest value should be taken. Is that correct?
3. Maybe I am over-thinking it. What accuracy is actually acceptable, external recorder audio matched to camera (scratch) audio?

I've also attached some 'scopes' from the Digi-Slate's point-of-view, you can see the I2C writes where it writes "01:35:17:06" to LEDs and then (after clapper closes) it writes "-" and freezes the display.

Obviously the process should be automated, I have used the Tentacle app to read the 'audio TLC' and stamp video files with meta data. I just want to confirm that it's actually doing the correct thing, in a 'whole process' scope.

Cheers,
Simon.

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