Re:Lepton image compression: saving 22% losslessly from imag...
by niftich on Friday July 15, 2016 @05:00PM
(#12103811)
The first part of your question was posed on Doom9 in 2009. It's the opinion of Dark Shikari, longtime lead x264 developer, that it would be possible [1].
Not sure what you mean by the keyframe removal, though. Such an act would be lossy, significantly impair any P-frames or B-frames (unless you majorly modify them), and, it frankly doesn't sound very reversible. Mind elaborating?
Re:Lepton image compression: saving 22% losslessly from imag...
by phire on Saturday July 16, 2016 @09:23PM
(#12108607)
What I mean is transforming I-frames into equivalent P-frames (or even B-frames) that decode to the exact same pixels. The transformation might result in something that is bigger than a directly encoded P-frame (which can tolerate some small errors) but I suspect the new P-frame will be smaller than the original I-frame.
There is no restriction that P/B-frames only reference I-frames, so you don't even need to touch those frames.
For conversion back to MPEG2 it would be ideal to detect or mark the original I-Frames, so you can convert them back (a simpler transformation). But you could also pick any random P/B-frame and convert it to an I-frame with little issue.
Maybe you could even go further and actively remove keyframes (in a fully reversible way, just keep a record of where they were)
I'm not sure how much you would save, and for losslessly archiving DVDs you might be better off creating a special format like Lepton for mpeg2