w4-bad-apple

Bad Apple!! music video on the WASM-4 fantasy console.

Building

First, you need to create a frames directory containing an image for each frame of the video. It's a lot of data, so I don't include it in the repository. To get the frames for Bad Apple!!:

mkdir frames
youtube-dl UkgK8eUdpAo
ffmpeg -i '<the file>' frames/%d.png

The music file for Bad Apple!! is included in the repository because it's small, not easily available anywhere, and the music system included here is rather specialized and probably won't work with other MIDI files. Thanks to @analog-hors for implementing it!

Build the cart by running:

cargo --release --features use-elias-gamma

Then run it with:

w4 run target/wasm32-unknown-unknown/release/cart.wasm

You can run cargo with +nightly -Z build-std=core -Z build-std-features=panic_immediate_abort and run the cart through wasm-opt -Oz -c to get a smaller cart, but it doesn't affect addressable memory usage and so won't help if the video is too big.

Customizing

Line 16 of build/main.rs contains a number of constants that can be used to adjust the quality of the resulting video, including frame size, downscale filter, framerate, and the video start frame and length. 4-color video can be encoded by putting four color in the palette and modifying src/lib.rs line 17 to 2 BPP.

If you try to encode a video that is too large, you will get a linker error saying the initial memory is too small. If this happens, you can modify the linker arguments in .cargo/config.toml to increase the available memory. Note however, that if you do this, the cart will require a modified wasm4 emulator.

If the --features use-elias-gamma argument is not present when building, Elias delta coding will be used instead. This saves space with large frame sizes, but Elias gamma coding uses less space with smaller frame sizes.