Frame Rates...How Does NLE Know?!?

[Norm Kaiser]

Hello, all:

I have a few questions. I'm perplexed about the subject of frame rate and how NLEs "understand" them.

Allow me to begin with some specifics.

I shoot with a Canon Vixia HF21, which captures video in AVCHD. The camera has several frame rate modes. The frame rate I shoot at is PF30, which, according to the documentation, is supposed to be 30FPS; however, in the documentation, there's a little footnote by the 30FPS description. The footnote says that the 30FPS is actually shot at 60i.

Now, that to me means that the video is actually shot at 60 frames per second, interlaced. That also means to me that in order to make the video 30p, it has to combine two of the 60i frames. Fair enough.

Hopefully I'm making sense so far.

Now, I would think that this combining of frames from 60i to 30p would be done in-camera. That's my assumption. Maybe I'm wrong.

Here's why I think I'm wrong. When I import my video into my NLE (Kdenlive), I set my project to be a 30FPS project, but the software screams that the project's frame rate doesn't match the clip! That is, Kdenlive is detecting the clip at 60FPS (59.96, to be exact).

So what gives?

And what happens when I render at 30FPS? If the software is seeing the clip as 60FPS and I render it as 30FPS, what does the software do? Drop the extra frames? And if the answer is yes, doesn't that mean the video is now interlaced?

So confused.

Any light would be so very appreciated!

Norm