MPEG-2: possible to get exact cuts?

[El Bart0]

I know with MPEG-1, you can only cut at every I-frame...is this the same with MPEG-2, or can I cut an MPEG-2 precisely at any spot?

[Cornucopia]

MPEG2 has the same frame sequence structure as MPEG1. This includes the use of I-, B-, and P-frames (in roughly the same order).

Your assumption that one or the other just does I-frame cuts is incomplete. Most editing apps that can deal at all with MPEG will only allow editing on the I-frame, whether MPEG1 or MPEG2.
There are those others that treat MPEG as raw video and decode everything when imported and used, and so will allow you to edit anywhere you want, but will only export an AVI (or frameserve to a new MPEG encoding). This is not such a good way, as re-encoding is always compounding the lossiness and artifacts.
There are a few apps that edit MPEG in a very smart way. They allow editing anywhere, and if it's not on the I-frame they will reconstruct the partial GOP and only re-encode that section.
Example:

[ IBBPBBPBBPBBPBBibbpbbpbbpbbpbbIBBPBBPBBPBBPBB ]

gets cut at the 1st "p" of the 2nd GOP and then is restored at the 4th "B" of the 3rd GOP. The 1st GOP (and other GOPs beyond the boundaries I set) won't be affected at all, although their timecode flags will be updated. The new sequence looks like this:

[ IBBPBBPBBPBBPBBi{p}{p}//{I}{P}{B}{B}{P}{B}{B}{P}{B}{B} ]

where the "//" is the cut and the "{}" is the changed frames.
Or it could be simpler and just leave full I-frames :

[ IBBPBBPBBPBBPBBiii//IIIIIIIIII ]

where the italics are the newly reconstructed and left alone frames. This works, except it makes the bitrate spike or lets the quality dip at those points.

Sorry, but you'll have to do your own research as to which apps will do which. Good luck.

Scott

[El Bart0]

Thanks for the in-depth info...but no thanks for leaving me hanging! Does anyone know which program will allow me to cut an MPEG anywhere?

[VidGuy]

I use mpeg2vcr from www.womble.com - it usually does a very good job at cutting and/or pasting.

[darshansingh]

I bought Honestech Video Editor 5.0 (the latest version) a few days ago for just this purpose. You have a choice of a FAST MPEG MERGE (cut at I-frame) or a SMART RENDER (cut at frame, re-encode affected GOPs).

[Cornucopia]

For someone who would be needing to edit MPEG often, on frames other than just I-frame, my money would go to either the Honestech, or to M2Edit. I don't like Womble (mpg2vcr). It corrupted a few of my files and has a goofy interface.

When I mentioned about apps that accept MPEG as source and work with as if it was std AVI, I was thinking about Premiere w/ decoder, but you could now add VirtualdubMod to that list.

Scott

[El Bart0]

Thanks for the tips guys. I'm going to be capturing stuff off TV mostly and I need the most effective way to get rid of commercials. I've tried cutting with TMPG but it's not perfect and accurate; I'm a complete perfectionist, so I can't have it that way! Thanks again.

[El Bart0]

Which Honestech program would I want? I noticed there's DVR, TVR, Video Editor, and MPEG Recorder? Do they all really do different things?