In 1990 I was fortunate to attend the World of Commodore trade show in Toronto Canada. The official show guide can be seen here. My best friend from high school was working for Free Spirit Software (booth 237) at the time, and we thought it would be fun if I joined him for the show. I remember walking the show floor and being blown away by a demo that I think was being shown by Great Valley Products (GVP, booth 226) to demonstrate how fast their SCSI controllers were at that point in time. As I recall, they were streaming a full screen animation from the hard drive and playing back the Walt Disney movie, "Snow White and the Seven Dwarfs". I've never seen this demo again and I've never heard anyone talk about it or reference it. I really don't know if it was a 'clip' from the movie or the whole movie; and I wonder about the legality of their demo (as I would guess Disney never 'approved' of the use of Snow White). But I clearly remember seeing it. Does any information exist about this demo or other 'speed demos' done by GVP that might confirm my memory or provide more details?
Here's a former GVP engineer talking about streaming the video clips from the Laser Disc game "Dragon's Lair" from one of their hard disks:
Maybe that's what you saw? Dragon's Lair's visuals are somewhat similar to a Disney animated movie after all.
And even if you're sure about the "Snow White" part, the engineer's statement at least confirms that they were doing this exact thing.
I don't have particular knowledge about that Commodore show or the GVP demo you saw. However, in late 1990, full-screen video playback was common already for many years on stock Amigas. This was demonstrated all the way back in 1986 with the "Juggler" demo. Longer videos required FAST RAM buffers, since the uncompressed (or lightly compressed) frames would quickly eat up the full 512K (A500) to 2M (A3000) of CHIP RAM.
Like the "Juggler" demo, the common use case was with applications like Sculpt 4D. These used ray-tracing to generate photo-realistic animated scenes that could be played back in real-time, though they might take days to generate. Typical resolution was 320x200 HAM mode and the frame rates were in the 24 to 30 fps range.
Doing the same real-time playback from a large video file stored on a SCSI hard-disk would have been an obvious way for GVP to demo the speed of their HD controllers. A typical 8-bit SCSI controller with DMA on an Amiga usually runs at about 2 MiB/sec. Each frame of the video files I am describing would be 48,000 bytes uncompressed (320x200x6 bits/pixel). So a 24 fps video would only need to maintain a throughput of ~1.1 MiB/sec. A DMA SCSI controller pre-loading the data to FAST RAM, then the CPU moving those buffers to CHIP RAM for display, seems quite reasonable. It might have required an accelerator with 32-bit RAM, but GVP was also selling those at the same time.