Really.....when you say that editing will go faster, what exactly do you mean? .... writing to the screen?

But I can assume no improvement in quality....

No, you can't add quality. ;-) The major advantage of MPEG compared to other video and audio coding formats is that MPEG files are much smaller for the same quality. This is because MPEG uses very sophisticated compression techniques. But, it's that same sophisticated compression technology that makes it very slow for editing. This is because The MPEG format does not store full images for each frame like DV or MJPEG. It uses three types of frames, I-Frames, P-Frames and B-Frames in a specific sequence of 6 to 15 frames to store the images. (ie., IBBPBBPBBPBBPBB). The I-Frames are the only frames that hold the full information. The P-Frames hold predictive information and the B-Frames only hold the delta image that has changed since the preceding I or P frame.

So when you stop on a frame in your editor that is a delta frame in the sequence IBB, the editor has to search back two frames to the preceding I-Frame and then rebuild the image using the previous B-Frame and the current B-Frame. That’s a lot more work then just showing the current frame in DV or MJPEG.

The real problem comes form adding or cutting frames. The whole file is a consistent IBBPBB… etc. When you add or cut frames, the whole file needs to be reencoded to match the sequence again. This is much different than an AVI file with DV or MJPEG data because in those files you just remove the frame and stitch the ends together with no re-encoding, That’s why we tell people not to edit in MPEG. MPEG is really a final rendering format. If you’re going to do a lot of editing on captured MPEG files, it may be better to encode it to an AVI file and make all your edits there and then render back to MPEG when you’re done.

~jr

jr,

Thanks very much for the comprehensive explaination.

I have done a fair amount of editing the MPEG2 file using MS3. It seems ok, but I can't really compare it to anything else since this is my first experience.

Should I go back and convert, then re-edit? or is editing MPEG just a longer process? I can live with a longer process...

Allen

If you've already done a substantial amount of editing on this project then stick with what you're already doing. The time savings you'll gain by converting to AVI will probably be nothing compared to what you'll lose by having to start the project over again.

For future projects though, you'll probably want to consider converting to AVI first. The increase in speed with which you'll edit and render and even just zoom and scroll around on the timline will be startling at least.