The thing is, the MPEG stream contains a few frames called I-frames that are complete in themselves, but most of the frames are B-frames, which are stored by storing the differences between the current frame and nearby I-frames. If your cut eliminates an I-frame, then you MUST recompress the B-frames that depend on it. (Things called P-frames also exist but considering them wouldn't really clarify the discussion.)
If you will... I've been reading about P, B, I frames for almost two years (even this: http://bmrc.berkeley.edu/frame/research/mpeg/mpeg2faq.html) and this paragraph seems the most comprehensible piece I ever seen. I mean, it finally made me understand it. Could you go on and explain the P-frames or point to any good link on this issue? Would help a lot! I've been trying to improve mpeg2 video compression under the limits of a readable-dvd using quantizers - "improve" meaning "reaching the maximum quality possible, not the size/quality equation"; size wouldn't matter in this case, as it's mainly for testing matters. A DVD can play a mpeg2 source at a maximum 9800kbps, but ffmpeg for example allows a limit of 9000kbps/maximum. I could work this around limiting the quantizers from 2-6 instead of the standard 2-31 (anything less than 6 would cause enormous amounts of buffer underruns), which made the kbps variable and the video would normally go up about 1000kbp/s when needed. The next question then would be: would it make sense to increase the number of B-frames during conversion as to increase "quality" - for the video would have more of "complete frames" and less I-frames? nice post, tks, flavio
