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 Post subject: Sega CD video codecs
PostPosted: Sun Apr 19, 2015 7:09 pm 
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Location: NE Indiana, USA (NTSC)
In this post, Sik linked me to YouTube video of a FMV sequence from the Sega CD game Loadstar, which has essentially full-screen software-decoded video at an acceptable frame rate and a bitrate that fits into 1x CD-ROM (150 KiB/s). How did codecs like this work?


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 Post subject: Re: Sega CD video codecs
PostPosted: Sun Apr 19, 2015 8:07 pm 
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Location: Rio de Janeiro - Brazil
That FMV is indeed pretty good compared to what was present in most of the Sega CD library!

I won't pretend I know anything about the codec used here, but inside the dark tunnels (and sometimes outside the tunnels too) you can clearly see what appears to be 32x32-pixel macroblocks, so I guess the compression scheme revolves around that.


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 Post subject: Re: Sega CD video codecs
PostPosted: Sun Apr 19, 2015 8:48 pm 
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It's just a variant of Cinepak made to work with palettes. The base blocks are 2×2, 4×2 and 4×4 with dictionaries for each size (with up to 256 entries for each). Anything that doesn't fit into those dictionaries has to be stored as-is. I don't remember how audio is stored, besides being streamed alongside video (the sample rate is quite low, though).

Not sure if this stands true for all versions (the decoder was being constantly updated over time and Sega controlled that only the latest version was being used, if the addenums are anything to go by) but I know that's how at least some of them work.

EDIT: or just look here instead of taking what I said for granted. I don't guarantee the accuracy of my statements =P (although that seems to be the gist of the basics)


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