CD-i member The MogMiner shares some technical background on *why* various CD-i games had these flat-shaded cartoon-cutscenes like in Zelda and Mario on CD-i

The Philips CD-i was technically limited and is known for a specific kind of animation that is used in a lot of CD-i titles (mainly games and kids titles): flat-shaded cartoon-like scenes mainly used in cutscenes; based on base-case CD-i specs (it doesn't need the Digital Video Cartridge), while still mimicking the idea of full-motion-video. The type of animation seems specific to CD-i (and to some extent, some early CD-ROM) and you might wonder is CD-i was not capable of doing anything better. Was it easy, was it cheap, or was it downright the best CD-i was capable of? TheMogMiner explains: "The baseline CD-i player spec, ironically, did not support the sort of full-motion video that comes to mind when we think of the "multimedia" heyday of the early 90's. MPEG decompression was simply not supported unless you had a Digital Video Cartridge, or had a model from pretty far into the console's life cycle, when manufacturers would sometimes integrate DVC compatibility into the console itself.  

The standard video hardware of the CD-i was an odd thing: One of the video modes (and the only way to break out of palettized color) was "delta YUV", where you'd specify the starting values in YUV color space, then each following sample was a delta against the current value. This was what a handful of games used to play FMVs within a small, limited on-screen window, since it provided enough color fidelity to be worthwhile. Beyond that, it's important to keep in mind that the baseline CD-i spec was sporting a 1x-speed CD: The best you could get, assuming continuous transfer with no seeking, was 150 kilobytes a second coming off of the disc. Given that a full frame of 320x240 pixels at 16-bit color resolution is exactly 150 kilobytes, that would seem to mean that the best you could hope for is a "video" running at one frame per second. That's not a video, that's a slide-show. 

CD-i member CDifan interupts: "Technically the max usable datarate is 75x2324 bytes per second, a little over 170 KiB per second. But that is with no error corrrection, suitable for audio/video but nothing else. For an example of what was technically possible with RLE , see the cutscenes in Burn:Cycle."

"So, how do we solve it? Well, the Apple IIgs had a prescient aspect of its own video hardware: It supported run-length encoding (RLE) for graphics. The CD-i spec called for video hardware that could do RLE, too. In English: RLE is a value and a repeat count. "Blue, 25 times" instead of "blue blue bl..." This was the key to compressing cutscenes to be small enough that they could be streamed at a reasonable frame rate. You'd load up a static background on one video plane, then stream RLE cartoons onto the second plane, layered on top. Easy. Now, none of this is meant to defend or approve of the atrocious art found in the CD-i Zelda games, or Hotel Mario. As RLE fills were limited to a single line (I believe), I can't think of a reason why some amount of shading couldn't have been done, as long as it was vertical.