[cnelson87]

I have an ADS Instant USB that records directly to mpg2. It works very well for recording TV shows and converting VHS tapes to DVD. The included mpg editor can edit mpgs at the keyframe level and is usually adequate. However, many times a keyframe will occur just before or just after a fade-in or fade-out, and I either have to sacrifice a few frames of content or leave in a few frames of unwanted material.
Question 1, is there any way to re-encode a single non-keyframe to become a keyframe so that I can create more accurate edits?
Question 2, when transcoding from mpg2 to mpg4, is there any way to ensure that the mpg2 keyframes translate to mpg4 keyframes? I don't know if that would produce better encodes, but it seems like it should.

[dlefebvre]

You ca transcode mpeg2 but at a cost. the mpeg2 format is optimized for playback, in theory you cannot edit it because it's not frame based. The video is compressed on a Group Of Picture pattern. Many software allow you to work around this limitation but at a cost. There is always a quality lost when you start converting from one compressed format to another. What you got from the start, you cannot improve. So the compromise is : Do you want to lose a few frames or do you want to lose quality?

[cnelson87]

Yup, I'm aware that transcoding from one lossy format to another, such as mpg2 to mpg4, is not ideal. However, it's really no different than ripping a DVD to DivX, and results can still be very good. I am no expert, but it seems to me that if you could use the same keyframes when transcoding, wouldn't that maximize quality? I dunno...
As far as editing mpg2, all I'm interested in is to be able to re-encode a single frame into a keyframe so as to make more accurate edits. Since the frame in question is either at the end of a fade-out or the beginning of a fade-in, the frame will be all black and therefore quality is of minor importance.
I Hope what I'm asking makes sense.