Kostya's Boring Codec World

There are some codecs that I’d like to RE (mostly for completeness sake) but I don’t have time for that.

Intel Audio Codec

This one seems to be a lot like its predecessor IMC (Intel Music Codec), it even codes coefficients the same way but with different codebooks. I’ve tried to hack IMC decoder to make it use proper tables but it still decodes garbage.

Along with Indeo4 decoder it would make our Intel codec family complete, but unfortunately we have decoder for neither.

ClearVideo

The codec that was present in AVI, QT and RealMedia. My investigations showed that it was not-so-fractal codec, it still codes blocks with DCT and even does that in simpler fashion than H.263. Though a patent assigned to Iterated System describes what can be the base of this codec: DCT-based codec that uses fractal search to determine the best code for the current block or something like this. Maybe that’s the reason why there are no Huffman tables in decoder while it obviously uses some.

RALF

That’s rather special lossless codec that stands aside from other RealMedia codecs: the file format was altered for that codec (so far I’ve seen only standalone RALF files, not, say, RV40+RALF).

It looks like the codec is rather simple and employs context-dependent codes instead of generic ones. I remember finding about eight hundred static Huffman tables in decoder for that purpose.

Also codec developers were very grateful to their source of inspiration, that’s why codec IS is “LSD:”.

WMA Lossless

Nothing much to say about it. As I remember, it uses infinite impulse response filters for compression and least squares method for finding (and maybe updating) filter coefficients. Should be not so hard to RE but nobody bothered so far.

M$ Screen 1 and 2 (aka WM Screen)

I’ve dabbled in REing MSS1, not MSS2 (which was later relabeled as WM Screen) but they should be related.

MSS1 was rather simple screen codec based on classic arithmetic coding (with adaptive models too IIRC) and binary partitioning. So decoding process was simple: get point for subframe division (horizontal and vertical) and modes for decoding those partitions (fill, skip, subdivide).

VoxWare MetaSound

This codec is obviously based on TwinVQ, it even has similar huge tables for different samplerates and bitrates and I found almost the same header reading code.

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In conclusion I want to say that if somebody wants to RE those codecs he’ll be more than welcome (especially for Apple ProRes but I don’t care about it much).

This entry was posted on Saturday, August 27th, 2011 at 6:42 am and is filed under RealVideo, Useless Rants. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.