Post
by LocalH » Fri Jul 03, 2009 4:32 pm
For everyday use (i.e., non-preservation) I would recommend using some sort of lossy compression (yes, I know, that allows the same type of situation as with ISO+MP3, but then again lossless captures of analog video are absolutely massive, and would also be losslessly "preserving" the composite artifacts inherent to the storage medium). By all means archive the large MAME-style CHDs for preservation, but who has the hard drive space to store GB upon GB of video for these games?
I would suggest something mature like I-frame only MPEG-2, pretty much any computer purchased in the last five years comes with an MPEG-2 decoder already installed, and even for those who don't run Windows/OSX or don't have MPEG-2 decoders installed, there are fairly simple solutions that can be either bundled with the emulator or pointed to by a handy guide. Plus, for the lossy version, you can also do a little processing to the video to make it more friendly to compression (and thereby increase quality at lower filesizes) - remove luma/chroma crosstalk, fix levels to compensate for the difference between NTSC TVs and PC monitors, etc. Also, if you have a little older computer that is still powerful enough to handle this, but may not be able to handle SATA drives or PCI-E cards, then you may not have either the HD or memory bandwidth to handle streaming that much lossless data on top of having to emulate two 68ks and a Z80 (not to mention the rest of the system).
Insofar as the video content on MegaLD games - I want to advocate against any deinterlacing whatsoever. If the video doesn't contain 50/60fps content, then it doesn't need deinterlacing at all, and if it does contain such content, then deinterlacing will cause us to lose 50% of the image data (except for low-motion scenes where the deinterlacer doesn't need to fill in missing lines). Most computers that can handle MegaCD emulation can probably also handle at least a dumb bob deinterlace in realtime on top of that (which is basically interlace "emulation", i.e. it shows flickering just like actual interlacing). Anything other than this can be included as an option but should definitely be done in realtime so the user can select the deinterlacing algorithm that provides the best quality on their machine while still being able to actually play the game.
I know from playing them years ago that at least SEGA's arcade LD titles used smooth, fluid 60fps content, so it would not surprise me if MegaLD titles did too, so I just wanted to bring that point up and make sure you guys were aware of that on the video side of things.
Another question: Are MegaLD games CLV or CAV? CLV allows more video to be crammed onto the disc as you reach the outer edge, while CAV discs are limited to one frame per revolution, or 54000 frames total. Due to the need to address individual frames (to branch to different video clips as per gameplay or for menus, attract modes, etc), I'm gonna guess CAV.
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