Capturing tapes twice with different results

[geohei]

Hi.

I noticed that when I capture a tape twice with exactly the same settings, software, configuration and system, I get two different results. The captured files slightly differ in size.

How is that possible?

The software used is Adope premiere 1.5, and capturing is done using "Scene Detect".

Thanks.

[junkmalle]

If you're capturing from an analog source, no two captures will ever be identical. Analog is prone to random electrical noise, tape speed variations, etc.

[geohei]

I forgot to mention that I capture using Firewire, hence it's digital.

[junkmalle]

Since this was posted in the DV forum I was guessing you were using a DV device. But I couldn't be sure if you were capturing from a DV camcorder tape or using a camcorder (or standalone DV box) as a passthrough to capture a VHS tape. I'll assume you're capturing from a DV tape since you don't mention otherwise.

Sometimes when you capture from a DV tape you miss a few frames at the beginning because the tape drive mechanism hasn't come fully up to speed. That would vary a bit from capture to capture.

It's always possible you dropped a few frames in the middle. I don't know if Premiere would report this as a error (I don't use Premiere).

What comes over the firewire cable isn't an AVI file. The computer adds the AVI wrapper information (a header for the entire file, and headers for each individual frame of audio and video) around the data as it recieves raw DV from the camcorder. This size of the wrapper data could be different. This is just speculation though.

[geohei]

Yes, I capture from DV tape via firewire. Sorry for not mentioning in the first article.

When I read your posting, I guess that the discrepancy comes from the first frames missing. However I was surprized to see that that out of 64 scenes, none (!) was identical.

Regarding the wrapper information ... as far as I understood the way it works, this wrapper information should be identical on each capture?

Anyway, thats a lot for your explanations.

Regards,