I still find Sega CD games interesting to review in this little journal, if for no other reason than giving people something to find when they search for obscure games using Google.
It should be noted that the Gens Genesis (and Sega CD) emulator is now open source and running on Linux. Ideally, this development should assist in reverse engineering efforts, should interested parties wish to investigate the multimedia technology employed on some of the earliest CD-based games.
The game took advantage of digital audio tracks for all of its music. The CD has 24 audio tracks. As for the data track, it contains an entire 1.5 megabytes of information. So the game retains its trademark compact size.
Followup: A reader reports: "Yup, it's just a shooter. Basically the same as Sol Deace, with a tiny bit of FMV on initial boot courtesy of Wolf Team's logo, and a few animated story sequences tacked on. Not sure if the FMV on Sol Feace was Cinepak; since it came with the US Sega CD's initial console it might have been something else."
The data track contains a file called autoexec. The root directory has directories for audio/, code/, icons/, misc/, text/, and video/. The audio/ directory contains a bunch of files with the extension ".20k*8". I take this to mean that the audio is to be replayed at a 20KHz frequency and a bit resolution of 8 bits. Examination of the data reveals that it is, of course, sign/magnitude audio.
The video/ directory is broken into a 3 more subdirectories which each contain a number of FMV files. The files follow a consistent interleaving pattern of 0x400 (1024) bytes of sign/magnitude 8-bit audio and 0x1EC0 (7872) bytes of image data. This is most likely raw Sega Genesis screen tiling data. If this is true, it should be pretty straightforward to render. Unfortunately, determining the correct color palette might be a bit tricky. There is no header on these files. As for the framerate, I imagine that would be driven by the audio output. The fact that each audio frame is 1024 samples complicates matters. It does not divide evenly into samplerates like 16000 or 20000. Perhaps the Sega CD audio unit was flexible enough to allow 16384 Hz (16 * 1024) or 20480 Hz (20 * 1024).
The game disc has 45 competently-produced audio tracks. The data portion of the disc contains almost 1200 files. Most of them are .prg (sub-program?) files and .pcm files. Given that there are 45 audio tracks, the latter .pcm files probably contain voice and sound effect samples. Each files has a header which includes the filename and several other fields. The actual data appears to be the same usual sign/magnitude PCM audio.
Followup: A reader reports, "It's a fairly simple game. You just click on buttons and an animation takes place afterward. No video, just a lot of animation. Not much to see here really other than some monty python-esque gags."
As can be expected, there are plenty of CD audio tracks (20). Track number 2 sounds like it consists entirely of sound effects. The data portion has, among various other files, 4 large files (5-30 megabytes each) with the extension .sdm: credits1, credits2, intro, and youwon. Browsing through them predictably reveals sign/magnitude PCM audio.
by Mike Melanson (mike at multimedia.cx).
Multimedia Exploration Journal
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