Two questions for the compression gurus here. Suppose you have a bunch of raw video. You take extracts of it and put them together to make a movie, M1. You make an H.264 encoded copy of that. Let's call it C1. You then make a new cut of your movie, M2, which is mostly the same footage as M1 except that you've shortened a few scenes and lengthened others. You make an H.264 encoded copy of that. Call this C1. When maki…
> You then make a new cut of your movie, M2, which is mostly the same footage as M1 except that you've shortened a few scenes and lengthened others.
Your new cut gets encoded from whatever you've chosen from frame-index numbers and timestamps in the various original raw yuv project files (or ProRes, etc, depending on what your camreas output).
The existence of the original cut should be irrelevent because what you're not doing is taking the compressed output product of C1 and re-cutting it into C2 unless for some catastrophic reason you have lost or deleted all of the original raw/uncompressed original camera files.
If you are generating new C2 from your original uncompressed (or lightly compressed) files, of course the encoder will be making new decisions on where to insert I-frames and P-frames based on the duration of each camera cut, changes you've made to CGI, other visual factors in the re-cutting.
> Suppose someone has an uncompressed source S. They compress it with a lossy compressor producing C and distribute C to you. You decompress C producing S'.
> You then compress S' with a lossy compressor (the same type that the original producer used--e.g.., if C is an MP3 you use an MP3 compressor) producing C'. I don't know about video, but for audio (at least back in days when MP3 was starting to get big) C' would be lower quality than C.
all of this is generally a bad idea unless you have no other option but to work with received files that are already compressed. say for example you're working on a documentary about something in a conflict zone and somebody sends you a highly compressed h264 file recorded on a smartphone. in this case there is no uncompressed original available.
you're going to want to first extract it into an uncompressed yuv raw file on disk so that you can work with it in your standard editor, and then whatever scenes you choose from within it will get re-encoded into your final output.