One live video feed, split across the keys of a Stream Deck.
Chain: none
Applied to the whole frame before slicing, so edges and pixel blocks stay continuous across key boundaries. The chain is ordered.
Generated in the browser: no camera, no network, no server. Mirrors the Python synthetic source.
Stays on your machine - the file is read straight into a <video> element, nothing is uploaded.
Your own feed across every key. The stream never leaves the page.
Talks to the Python service in this repo, so the same pipeline drives the browser and real hardware.
Grid and key resolution match the real hardware, so each key canvas holds exactly what the device would receive.
Turn skipping off and watch redraws skipped fall to zero.
Dividing the frame width by columns and height by rows is the obvious approach, and it is wrong: a Stream Deck key is square, so 16:9 cells arrive stretched. The frame is cropped to the deck's aspect ratio first, then divided, so every tile is square and the mosaic lines up.
Pressing a key pushes that key's rectangle — in source pixels, not screen pixels — so the whole deck becomes the inside of one key. How far it goes is pure geometry: an XL divides by 8 across, so a 720p frame is spent in a single press, while a Mini (÷3) manages three levels. Past 1:1 the badge reads interpolated, and the stack refuses a press that would leave cells with almost no pixels in them.
Mean frame difference catches a whole tile changing but a small fast object averages away to nothing. Changed-area — the share of pixels moving past a noise floor — catches the small object but ignores uniform drift. A key counts as moving if either fires, and that verdict is what decides whether the key is redrawn at all.
Only keys that actually changed get redrawn. On a static scene that is the difference between 32 redraws per frame and none; the redraws skipped figure in the telemetry panel is measured live, not quoted. Turn the switch off and watch it fall to zero.
Every frame is read back out of the canvas, so a feed served without
Access-Control-Allow-Origin taints it and takes the
filters and the motion detector down with it. NASA's public asset host
sends the header and honours range requests, so the footage streams in
and stays sliceable. Embedded players and the public HLS endpoints do
neither, which is why they are not offered here.
The grid maths and motion detector exist twice: Python for the hardware pipeline, JavaScript for this page. They are deliberate ports of each other, and the Python test suite is the shared specification for both.
Off this page, the same pipeline reads a Reolink snapshot endpoint or any MJPEG stream and pushes tiles straight to a Stream Deck over USB HID — no polling a folder of JPEGs through a local web server.
pip install -e ".[server]"
cp .env.example .env # set your camera details
slicedeck --serve # http://localhost:8080
No camera to hand? slicedeck --source synthetic runs the
whole pipeline against the generated scene.