Frame Rate -- Does it matter?

[mikecito]

I openly admit to my ignorance on the topic...

I previously exported from Premiere to mpeg2 via CCE's plugin. I would use the 23.98 frame rate, and then pulldown to 29.97 in order to accept the stream into my dvd authoring program. Using this method, I had to stretch the audio afterward to make up for the difference in 23.98 and 23.976 frame rates.

I recently bought Premiere 6.5, and realized that it comes with an encoder for mpeg2, so I gave it a try. While I was at it, I tried to encode directly to 29.97 instead of 23.98 and then pulldown.

Here's where I'm confused: When I encode in premiere to 23.98, and then pulldown, I THINK I get the same result as if I just encode to 29.97 fps in the first place. If I encode directly to 29.97, I can skip the entire audio stretching process, which takes a couple hours. Am I missing something? Is there a reason I wouldn't want to do this?

Thanks in advance!

Mikecito

[slk001]

The benefit of encoding at 23.976 and then applying a 2:3 pulldown, is that you are allocating your bits across only 24 frames, instead of 30. This essentially gives you a 25% increase in encoded bits for each second.

An example:
You are encoding a 10 second clip at 5Mbps. At 30 fps, there are 300 frames, or approximately 166kbits per frame.

At 24fps, there are 240 frames, or 208kbits per frame. You then apply the 2:3 pulldown (at no bit penalty) to get the same 300 frames as above.

So, you have increased the bits per frame by 25%. Plus, you no longer have to deal with any interlacing artifacts during your encode.
This is of course assuming that your original source is 24 fps FILM.

Why don't you just encode in CCE at 23.976fps? I do this in Premiere all the time. I guess that I don't understand why you have to "stretch" your audio.

[mikecito]

The only options in Premiere's video frame rate are ... 15, 23.98, 24 ...

Are you frameserving to CCE's external encoder? I can't find a 23.976 using the plug-in... am I just looking in the wrong spot?

Thanks for the info - I was actually wondering if that was why. :)