A Quick Look on IMM4

So I’ve spent an hour or so to look at IMM4.

What do you know, it’s a very simple IDCT codec with interframes. Intraframes have only DCT with usual run-level VLC coding, interframes have skip flag to tell whether this macroblock should be skipped or there’s a difference to the previous frame coded or intra block. See, no motion vectors, quantisation is single value per block (except for DC in intra block), there seems to be no zigzagging either. You cannot get much simpler than that.

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