OT: Increasing I-Frames - any drawbacks?

ScottW wrote on 10/29/2004, 11:53 AM
I've been experimenting with DVD Lab Pro (which, by the way, is a pretty impressive authoring tool).

I took the video from a motion menu and I'm breaking it up into 3 segments (so to speak), the first is the intro, then the buttons appear and it loops with the buttons and then when something is selected we continue on after the loop point. This is all in the same menu video so that I can keep things fairly seamless as long as I'm careful with how I design the audio (the loop is great, and I'm playing with a couple ways to handle the selection transition).

Anyway, the individual points in the menu video must happen on a GOP/I-Frame, so I've been rendering the Mpeg from Vegas with the I-Frame setting at 3 rather than 15 (the default) so that I have more granularity over where I set my points.

So far, beyond the slight increase in the size of the mpeg, this seems to be working pretty well and my testing on a couple of players has produced excellent results.

I'm wondering though if anyone is aware of any ramifications on the compatability side because of the increased numbers of I-Frames?

It's too bad that there's no way to change the I-Frame count dynamically for selected sections of the video or a way for Vegas to tell the encoder, "Please insert an I-Frame here" because that would be a good way to solve the chapter mark issue that people have. Not to mention if I could select the exact point for an I-Frame when I'm creating my menu it would make things a lot easier.

Thanks for any discussion,


cworld29 wrote on 10/29/2004, 12:14 PM
Well I for one have not had any reason to mess around with those settings yet. What does it do to your render time? I would imagine this would increase some.
ScottW wrote on 10/29/2004, 12:18 PM
Since it's a fairly short clip (about 1 minute), I've not noticed any change in the render times, but then I've not gone looking for any change either. Render time isn't that big of a concern to me since this is just the menu video.