Why are I-frames so important?

prairiedogpics wrote on 9/18/2006, 8:19 AM

I'm pondering the upgrade to V7 + DVD4, and I keep reading about how excited people are about specifying I-frames.
Can someone please explain to a novice why this is an important feature?

Thanks,
Dan

Comments

ScottW wrote on 9/18/2006, 8:25 AM

An I-Frame is a complete frame. B & P frames are used to describe changes in in the video from the preceeding I-Frame. Since the I-Frame is a complete frame, this is where a chapter mark must be positioned when authoring a DVD. Since I-frames typically occur every 15 video frames (using the default settings for the encoder), without the abiility to force an I-Frame, a chapter mark you specify in Vegas could be off position by as much as 1/2 second in the final DVD.

Now if I could just prove to myself that this new feature in Vegas works as described, I'd be much happier. edit: and I think I just did; GSpot seems to be not reporting things entirely correctly.

--Scott

TheHappyFriar wrote on 9/18/2006, 8:26 AM

it's important to many of us because dvd chapters should only be on real frames, AKA i-frames. So if it's not on an i-frame dupilcators have fits & some players can have fits.

prairiedogpics wrote on 9/18/2006, 8:36 AM

That makes sense. Thanks for explanation. It also explains why when using scene selection with DVDs I've authored with DVDA2, I sometimes don't enter enter the chapter exactly where expected...

If anybody has a link to a tutorial explaining I, B, and P frames in layman's terms, it would be much appreciated.

Always learning....

Dan

ScottW wrote on 9/18/2006, 8:44 AM

go to www.doom9.net and click on The Basics - they've got some good tutorials there about various topics.