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CAT Compression - If it fits, I sits!

Brilliant work. The 80x60 version is impressive in itself, but the deep-dive into extending the resolution is fascinating.

This is a great examination of many of the old tricks used to fake high res graphics on old limited systems. Really takes me back.

Old demo coder here just saying this is awesome and it brought me back!

Prioritizing audio over visual playback makes prefect sense, as humans are way more forgiving of visual stutter/discrepancies than of audio issues. As well as the variability of the amount of processing needed, as you mentioned.

It’s impressive to see your home brew running such an easy to recognise demo… I daresay you feel rather chuffed at just how much you can achieve with a machine you’ve created from scratch 😊

It is great to see the computer being used just for the sake of doing something. It shows that it really is a whole working system. Congratulations! Great explanations, as always. Thanks!

Extremely impressive, James. Seeing how you solve technical / programming challenges has always been the most interesting content on your channel for me, given your expertise. Thanks for sharing your incredible knowledge and skills with us!

Saw that amazing demo first. Now time to see all of the backgrounds... Edit: impressive work! Thank you for your clear explanations and for sharing your work. Very inspirational!

Can it run Doom, can it play Bad Apple .... I love it!

Nice work James. Very clever implementaion. !

Ahhhhh finally got to Bad Apple :D Gotta say it's been great watching this long term project grow over time :)

Love the work you do. Look forward to every episode. ❤

Facinating and humbling. Still thoroughly enjoying these vidoes! Great stuff. 👍

Magnificent! If you do plan to do more music on the synth, it might actually be good to add a channel that's a white notse generator. You can do a much more convincing hat or snare by passing white noise through an ADSR (the snare has something like a tom on a second channel, perhaps).

That's an impressive result on your demo!

very cool, thank you!

That's so impressive !

absolutely insane achievement. 💪!!!!!

Awesome job! Very crisp edges and great job keeping up with the transitions! I see the 4Mb file size, maybe I missed it but what did you end up with for a compression rate compared to the uncompressed down sampled source frame images? Have you thought of using your UART as an audio output? Drop the serial and hook the output to a speaker with a resistor and capacitor to limit the current and smooth it a little? Since you have a 8 byte output buffer on that already you could output 1 bit audio without any additional hardware and that buffer might make the code not too bad. If you just left it at the 115,200 you'd need to pump out 14,400 bytes a second, or 240 bytes a frame. I don't know if your SD card transfer rate and free CPU time on the Video decode would allow that without reducing the framerate, but I'd bet 115 KHz 1 bit audio would sound pretty good! Obviously if you reduce the output rate of your UART you could drastically reduce the bitrate of the audio. I wonder what the minimum acceptable 1 bit audio quality would be? Think you could squeeze that out? Thanks for putting this out there! There is not enough content explaining how to actually DO one of these demos with specifics. I know this video would have been a HUGE help and time saver when starting work on my own Bad Apple! demo. It would be neat if you took some time to get into the guts of your encoder for the video and how you sliced and diced the MIDI. Love this content!

awesome!!😍

An incredible amount of work and time.

It turned out incredibly well. Kudos! It´s right there with the demos for the best performing 8bit computers I've seen. I wonder if rasterizing vector graphics would compress it even further. There is a version made with a fourier series XD

James I just had an idea - you quite possibly can play samples on your sound hardware through the volume register. Just send singed integer formatted samples into the volume register!

impressive!

Fascinating journey 😁 when I was young I fall in a rabitt hole of creating fonts or electronic components symbols on millimeter paper 8x8 matrix (for ZX Spectrum)... for a moment I wondered why not create all possibilities but I already know binary system well and realised it be 2^64...😅

This is of course amazing as-is. as ever. Good problem solving. Feels so ridiculously modern with a trace of retro. Hats doffed. tipped and whatever else one does respectfully with hats. And, for once. I am an expert (eh as much as anyone is). and if this makes it into the open... will be happy to fiddle very slightly with some of the values in that demo to give my take on OCD concert-pitchish perfection and percussive filth ;)

I've not even watched it yet and already hit the like button.

Mind. Blowing. %)

So cool! I wonder if you can stream sprite changes as well. Could create some interesting opportunities.

Nice little project for the CPU! I’d recommend looking into the Heatshrink compression library for future projects, if you haven’t already. I can verify it’s suitable for realtime video streaming on microcontrollers.

Great work! I was thinking about the problem of being stuck with the vertical blanking period for writes a while back and the only workaround I could come up with would be a 30Hz mode, where, during one frame, you write everything out to a 1MB frame buffer while you display the frame, and on the second frame, you read back from the frame buffer, freeing up your primary graphics memory during the entire frame for writes. But that increases the complexity of the video hardware so much that I just don't know if it would be worth the engineering on a home project. Thanks for your videos in general, as I really enjoy thinking about these sorts of issues.

Interesting. To be honest your audio setup is decent given the constraints. I really like the retro square wave sound it has. What's missing is a bit of polish on the analogue side of things. In particular you need a low pass filter somewhere after the mixer to get rid of aliasing and any other unwanted noise. You'll probably have to experiment to find a good cut off point.

It would be fascinating to see a couple of the frame transitions slowed down significantly so you can see the block-by-block updates happening. Taking the existing encoding and doing one operation every few frames?

Great work and explanation as always! One question: how many LOC do the sources of the player binary have?

Hell yeah

Stunning work, yet again - great job! And sympathies on the audio struggles - I think your approach made a lot of sense given the limitations you had, though. And you're actually wrong when you say none of your percussion sounds are going to impress anyone - the bass drum you made at the end is quite good, I like that a lot. Here on out is unsolicited-suggestion-ville, so take from it what you will: if it were me, I'd like to add a noise oscillator - either replacing one of the existing square-wave channels or augmenting one or more channels with that functionality. There's ways to generate analog noise directly in hardware - transistor noise is one I've heard of and seen from folks like Moritz Klein - but there's also a very famous sound chip that generates 1-bit noise: the General Instrument AY-3-8912 used in (for example) the Amstrad CPC computers. Basically, it has a hardware random number generator (I think it uses a linear-feedback shift register, like the NES APU does) and instead of switching between 1 and 0 at the frequency you set, it switches to the next random bit value at the frequency you select. That should be enough to generate some fairly convincing white-noise-like sounds for your hi-hats and cymbals, and as a bonus you can get some nice rumbly blasts for explosions and such in your games.

I'd definitely be curious to see what could be done if the pallet was played with as part of the video stream, beyond the colour inversion. My first thought would be to chop the video up into sections with a dedicated pallet each, for higher resolution, though there's probably way further you can go than even that. This is a seriously impressive demo, I love it

Back in the day (1992), we used to play with VGA on a 80286 PC and the recently arrived SoundBlaster (that costed a fortune). We were using the 640x480 16 colours mode. You mention 60fps, we were doing half of that, but we were "hiding" the updates: in the 256kB of a standard VGA, there is enough space to "draw" the next image offscreen and reveal it with a simple "out" (I think it was to 0x3c4). Also, in that mode, we only used the 16 grays and the data was pre-rendered (we used PCX as a base standard, minus the header) to only recalculate it into the chroma data (and offset to have more tints in the light shades than in the dark), all that with a bunch of SHLs. Maybe you don't really need to go 60fps? For the sound, as you already (kinda) went to MIDI instruments, why not going to an OPL4 chip (or did I miss an episode?) such as the YM2515 and simply upload the instruments to the chip, and leave the sound problem for later?

That was really interesting, thanks James. I do a lot of retro-gaming conversions and emulation etc, and these kinds of optimisations are always interesting to me! (currently trying to convert Missile Command to my tile+sprite based platform on the old 8-bit Arduino, with composite output, using a similar idea of tiles with partial line segments) Out of interest, did you consider a frame-direction byte, so the data is rendered to the buffer either horizontally or vertically? Also a byte at the start of the frame to choose the tile-set to use, which could be more optimal for the frame? Your audio section reminded me of Tim Follin's ZX Spectrum music - that dude was a master at getting amazing sound from it's little beeper :)

The world is full of unsung genius.

What year do you think this computer could have been built with equivalents of that time. And would it be an impressive computer of the time? Very impressive project from start to finish!

Could you have somehow programmatically determined the best tiles for video? Maybe split the each frame into tiles and then find the closest ones and combine them? Also could you have changed the pallet frame to frame to be able to have the best tiles for that frame?

It sounds like you need a hw random 8-bit number generator you can hook up to the audio circuit to help with noise style outputs?

The different parts of the song ended up not being in tune with each other in terms of how they’re transposed. Should be fixable? I mean like the long low notes (bass) that play alongside the melody.

the link on the bad apple vid thats supposed be to this vide is broken (on its description)

To quote a Monty Python script.... MY BRAIN HURTS! When you were building the audio device, I always wondered why you did not incorporate timers to generate various tones, paired with digital volume control chips? Sure, they would be square waves, but with volume modulation, you could make a nice sounding output. Add another timer to the actual volume control chips and it could modulate without the need of heavy CPU work. Sure, this would have two timers and half a volume chip per channel, but it would not be very complex to make. I understand not designing a computer to run demos, but it would certainly make games much more interesting.

Man, if I ever get this far along in my diy computer project I want to try a "gpu" with sprites that support rotation, scaling and skew. back in the day IIRC, I saw some code that did all three operations at the same time (but line by line) with some "simple" matrix math (I hope I'm not mis-remembering this.. it was 20+ years ago in a little library called allegro 3) and I imagine it could be done "reasonably well" in hardware with fixed point math and a lookup table. Hmm. But then you'd want the gpu to be able to do the math to offload the work from the cpu. so do you actually support math, or just limit the features to some stuff that can be pre-calculated? feh. The imagination runs wild :D

Do you really need to decode the entire frame before vblank ends? Don't you just need to stay ahead of the current scan line?

hope you decide that you really do need to improve that audio. I've watched computer development over 76 years and don't really remember that rough of audio in any computer I've had. We all have our own definition of "adequate" I guess. Still, would be nice if the sound was less grating - after all, we understand tech better today and you do have precident (ie we didn't have SD cards back then)

Have you had any will, and any success , collaborating with other people on either the software or hardware that interests you?

Touhou mentioned

"Doujin Circle" isn't a proper name, it's a description of the group. "Doujin" means "same person" meaning "self-published". "Circle" just means "group". In the case of music, you'd translate it as "Indie band". "Alstroemeria Records" is thus the name of the group rather than a record label like the name would suggest.

why not start a new series, implementing CPU into an ASIC, and sending it to Tiny Tapeout

>Hopefully you've had a chance to watch the Bad Apple demo ... Which posted one minute after this video, haha

The graphics is putting the audio to shame.

No accounting for taste, in general I find this demo, weird, but then again that is my opinion of most Japanese (anime) stuff. I do however appreciate the technical merits of you getting it to work on your system. That is a real accomplishment. Hopefully your next choice will sound and look better. To set the bar, the scrolling parrot demo looked better. Your 3d demo looked better.

why is it always Bad Apple? Bad Apple here, Bad Apple, there, Bad Apple EVERYWHERE. God, I hate Anime.