Toaster

Toaster hears whatever is playing on your PC (Spotify, YouTube, anything) and writes it out as live Strudel code in front of you: named lines typed into a blank window and lighting up as they play. Around the code: every hit as a domino, your webcam with effects you work with your hands, a dot orb, or a little world. Toaster, as in Toaster Strudel.

Try it in your browser · Download for Windows or Mac

It finds the beat, the kick, clap and hats, the bass line, the chords and the key, and keeps rewriting the code as the song moves. It's a live reconstruction for show, not an exact transcription.

• Writes the song as code you can play. A line for each part, typed the way a live coder performs it (what you'll see in the code). It's real Strudel: press O and it opens in strudel.cc, ready to play; press X for the whole song as Strudel code and as a MIDI file.
• Your camera, worked with your hands. C turns it on. Frame something with your fingers and a window opens on it through one of 16 filters; make a circle with your hands and a portal opens, your own skull in X-ray first; ✌️ for the next theme, 👍 to record. K cuts you out over the visuals, or turns you to dots, voxels or glass.
• Visuals that move with the song. V for the background: the sound as a landscape, planets cut on the kick, liquid chrome, a tunnel and more; P for the dominoes or a punchcard; R for a dot orb that changes form every 8 bars; G for a lens of liquid glass.
• Little worlds. The scenery: thirteen scenes, from a lighthouse at sea to space to an eye that dives into its own pupil, every one answering the drop: hit D when it lands. Z hides the code and keeps just the visuals, for a live DJ set.

Windows 10 or 11, or macOS 13 or later. A webcam is optional.

Windows. Download Toaster-<version>-win-x64.zip from the Releases page, unzip it anywhere and double-click Toaster.exe. The first time, Windows may say "Windows protected your PC" (the app isn't signed): click More info, then Run anyway. It starts listening straight away; there's no prompt.

Mac. Download Toaster-<version>-mac-universal.zip from the Releases page (one app for Intel and Apple silicon), unzip it and drag Toaster into Applications. It isn't signed by Apple, so the first time the Mac won't open it: open System Settings → Privacy & Security, scroll down to Toaster and click Open Anyway. It asks to record system audio. Allow it. That's how Toaster hears what's playing; it doesn't record the screen, and the camera stays off until you press C.

Play some music: within a few seconds it finds the beat and starts typing. Press ? for the keys.

Updates. When a newer Toaster is out, it offers it a few seconds after it starts. On Windows, say yes and it downloads it, checks it against the checksum GitHub lists for it, closes, and opens again as the new version (your settings stay); on a Mac it opens the release's page. You can turn the check off in the help (?). The first time a new version opens, it shows what's new in it, each with its key, and the help keeps the latest additions at its top.

These are the keys as they come; every one can be changed in the help (?): click a key, press the one you want (a key that's taken swaps over). Esc, ? and F11 stay put.

The background and its strength, blocks, orb, card, glass, theme, camera effect and drop-effect choices are remembered between launches, and so are the keys; the camera always starts off.

V steps through them; A sets their strength, or for some their look (see the keys above).

• Spectrogram is what Toaster hears, as a landscape, and what it makes of it: the sound rises out of a floor in glossy hills, the frequencies across it (the bass at the right, the highs far off to the left), a bar of time rolling toward you from the back, louder taller and further up a rainbow from orange through green and blue to violet and white (after the 3D spectrum analysers); a faint line crosses it on each beat and a bright one where the chord changes, named at its end, and each time Toaster recognises something a pin rides along with the code it became, bd on a kick, cp on a clap, hh on the hats, each bass note as the code writes it (e1, a3).

• Cuts gives each drum a scene of its own, cut to on its hits, each a view of the song in Toaster's look: the drum's word huge, its line of code magnified, its 16 steps as a punchcard, the spectrum falling in dots, the waveform, you or the cover in big dots, the tempo and key, the spectrum as text mirrored both ways like a kaleidoscope, a tunnel of rectangles flowing out (those two after rentalunit5's video-synth pieces).

• Spiral and pitch wheel are after the visuals Strudel draws: the spiral is time going round, a turn a bar, every kick, clap, hat and bass note a mark where it fell, the newest bar outside; the pitch wheel has the twelve notes round a circle, the chord drawn as a shape between its notes, the bass note as a line out from the middle and the melody's notes as dots that fade.

• Warp is a feedback shader in the style of Hydra patches (its own, not Hydra): stripes folded into a kaleidoscope, trailing and swirling toward you, the kick punching the zoom.

• Fire is the old Doom fire in square pixels, lit by the song: it burns steady along the bottom, a little lower where the spectrum is quiet (the bass in the middle, the highs out at the sides); the song sets how high it reaches, the kick lifts it and the hats spit sparks. It burns low under the code, and smoulders while the song is quiet. When it comes on, and on every drop, it flares, leaping to twice its height and dying back (an idea from not.axel on Threads).

• Worlds is a film of planets, after Anthropic's Claude Opus 5.5 launch film: the kick on each bar's one cuts to another world on the same horizon (every other bar with fewer flashes), an extreme close-up of something (honey, agate, lace, a leaf, bread crust, plant cells, oil on water, a circuit board, the code itself) seen as a planet from low orbit, the foreground soft, gold dust in the air; when the kick drops out the film rests on a horizon at dawn till it's back.

  

• Chrome is a pool of liquid chrome seen from above with an oil-slick film on it: every kick drops a bead where it lands in the bar (so the rings spell out the kick pattern), claps strike lightning in the sky it mirrors, the bass swells it and each chord gives the film its own colours (real thin-film interference over the visible spectrum); every two bars a collage cuts into it: mosaic, dragged rows, a barcode, the liquid's contour lines, a dither, graph paper, and a panel with the song, artist, key and tempo.

• Scenery is the calm one: little worlds drawn in solid colour, characters and pixel art (it began as an ASCII landscape, after Claude FM's ASCII world): snowy mountain ranges, lit on the face toward the light and shaded on the other, mist in the valleys, a shore of pines and trees in blossom, a lake that mirrors it all, a meadow of grass and flowers, and a little toaster fishing from a rowboat out on the lake. On a light theme it's day (a sun, clouds, a flock of birds); on a dark one, night: a full moon, a sky of stars by the real counts with the Milky Way across it, fireflies over the grass. It glides past a step a beat, each kick ripples the lake and dips the toaster's float, the grass sways and the fireflies blink more when the hats are busy, the toast pops up on a drop, and every 8 bars birds cross or a star falls. A picks the scene, or auto, a new one each song:

  • The lake (the landscape above)
  • The sea, always at night, a red and white lighthouse on a rocky headland with the keeper's cottage beside it, its two beams sweeping round every two bars and flaring at you on each bar's first beat, the Milky Way rising over the water, the moon's light broken on the waves and running up the wet sand, foam on the kicks, a crab walking the beach, the toaster fishing from a rock
  • A campfire in a clearing in the pines, its flames leaping and roaring on the kicks and its sparks flying with the hats, a tent lit from inside, the toaster toasting bread on a stick
  • The snow, a log cabin on a frozen lake under the aurora, its curtains drifting with the beat and flaring on the kicks, snow falling thicker when the hats are busy, the toaster ice fishing
  • The city in the rain, a street across from a row of buildings whose windows go on and off a few each bar, a shop with a neon sign (TOAST), towers whose red lights blink on the beat, the rain heavier when the hats are busy, the puddles rippling on the kicks, a taxi going by every 8 bars, the toaster on a bench under an umbrella
  • The garden, a koi pond in spring under a red drum bridge (its reflection closing the ring), the koi swimming their rounds and darting on the kicks, a cherry tree in blossom, its petals falling thicker when the hats are busy, stone lanterns breathing with the loudness, a pagoda on the hill, the toaster on top of the bridge dropping crumbs on each kick
  • The falls, a waterfall pouring between cliffs of cracked rock into a pool, its water in unbroken streams that quicken as they fall, a dimmer sheet behind them, the pouring faster with the tempo, a surge of white racing down it on each kick and spray thrown up from its foot, the whole falls swelling on a drop, its mist rolling up, a rainbow in the spray by day (a moonbow at night) and an aurora over it all at night, the falls and the aurora mirrored in the pool with foam drifting off across it, a trout leaping every 8 bars, the toaster floating in the pool on an inner tube
  • Halloween (auto picks it only in October), a graveyard on a hill under a great moon, a black wood along the hill and a bare tree reaching across the moon, the toaster flying across it on a broomstick in a witch's hat (its hat lifted when the toast pops), bats flitting round the moon, their wings beating with the beat and their eyes glinting (more of them when the hats are busy), mist and will-o'-the-wisps among the graves, jack-o'-lanterns at the front, each carved with its own face and lit from inside, flaring on the kicks, and every 8 bars a ghost rising from a grave; by day it's dusk, the moon a great banded sun going down and everything else in silhouette
  • The sharks (after stackedlol's ascii-sharks), shallow water seen from above, a hammerhead, a blacktip reef shark and a zebra shark circling the toaster on its float, each drawn as tiles of colour with a glyph on each, its hide shimmering, schools of little fish (a stroke each, along its way) scattering from them, a bait ball of them circling the float, pulsing on each kick, which the sharks charge on a drop (and every 8 bars, when the toast pops), cutting through it over the toaster till it scatters, after which it gathers again, each kick rippling out from the float and making the fish flinch; by day the light's net drifts on the sand beside their shadows, by night their wakes light up the plankton
  • The festival, always at night, a stage on the far shore of a lake in the mountains, the toaster DJing at its decks in headphones, a sign on the truss lit up (TOASTER), its lights' beams fanning up into the sky and sweeping round every two bars, flaring on the kicks, the screen behind the decks playing the music as bars, the speakers thumping, the show's colours changing every 8 bars; fireworks going up over the mountains every 8 bars and on a drop, bursting into streaking sparks; the crowd at the water's edge against the light, heads bobbing on the beat, glow sticks and phones up, every arm in the air when the fireworks go; the lake mirroring all of it
  • The koi pond, seen from above, five koi (a kohaku, a showa, a sanke, a yamabuki and an orange ogon) swimming slow rounds of it, each drawn as tiles of colour with a glyph on each, their fins and tails see-through, a little faster on the kicks; lily pads in the corners, two in flower, the koi passing under them; the toaster on a lily pad of its own, a ripple spreading from it on each kick; when the toast pops (every 8 bars) the nearest koi comes for the crumbs, and on a drop they all do, gathering round the pad like the petals of a flower; click the water to drop food there and the three nearest come to it; by day the light's net drifts over the pebbles beside their shadows, by night fireflies glow over the water

The code is typed the way a live coder performs it: a part that stops gets a _ in front of its name (Strudel's mute) and loses it when it comes back, a part never heard yet stays a comment, and a change lands on the next bar line, the way ctrl+enter on the downbeat does (the line flashes, and the rest of the code with it). Now and then a closing bracket gets left out: a red error shows, then the caret goes back to fix it.

• The filters sit on sliders, .lpf(slider(850, 100, 4000)) (Strudel draws a slider in the code for that); a thin track under each shows where the value is in its range, and when the music's filter moves, the number slides there instead of being retyped, like dragging the slider.
• A bass whose filter sweeps on the 8ths, triplets or 16ths (dubstep's wobble, riddim's pulse) gets Strudel's filter LFO, locked to the bar: .lpsync(8).lpdepth(3) for the 8ths, with some resonance and grit. The export writes it the same way.
• When the chords pump under the kick (sidechain, in most house and EDM), the kick gets .duck("2:3").duckdepth(.6) and the bass line and chords go on orbits 2 and 3, the way you'd set that up in Strudel. The depth follows how far they dip.
• The tempo line says // breakdown while the kick is out for a bar or more, and // drop for the first 4 bars after a drop.
• A line too long for the window (often, in the vertical layout) goes on over more rows, broken before a method call and indented, the way you'd break up Strudel by hand.
• Half-time music (dubstep, much of trap: the snare on 3 alone) is written the way its producer would: the bar starts two beats before the snare, the kick on 1 and the clap on 3, rather than the claps read as a 4/4 backbeat a beat off. A slow song heard at double its tempo (a ballad at 85 counted as 170, its backbeat landing once a bar) goes back to its own tempo, the snare on 2 and 4.

• M records the window with its sound into Videos\Toaster on Windows, or Movies/Toaster on a Mac, as an MP4 ready for TikTok, Shorts and Reels. Switch to the vertical layout (L) first for a 1080 x 1920 video; it keeps everything clear of the edges Reels and TikTok trim on tall phones.
• J turns on drop clips: the first two drops of each song are saved as their own videos (the build-up and the drop) into that same folder.
• X exports the song so far into Music\Toaster on Windows, or Music/Toaster on a Mac: a MIDI file (drums, bass, chords and lead on their own tracks) and the whole song as Strudel code, every 4 bars as heard, the different ones named and played in order with arrange(). Paste it into strudel.cc and press ctrl+enter.

More on all three in docs/how-it-works.md.

Everything Toaster hears and sees stays on your machine. The sound is worked out in the app, and the camera (off until you press C) is looked at by the system's own face detector (Windows' face detector, or the Mac's Vision framework) and by Google's MediaPipe, both running on your machine. Nothing is uploaded. It reaches the internet for two things only: GitHub, when it starts, to see whether there's a newer Toaster (turn that off in the help, under Updates), and strudel.cc when you press O (your browser opens it with the code in the link).

• It does best with a steady beat. A song without clear drums can take 8 to 20 seconds to find one; tap Space on the beat to give it the tempo.
• The song's title (and its cover, for the ID card) come from the system's media controls (Windows' media controls, or the Mac's Now Playing), so any player that shows up there works: Spotify, browsers and the rest.
• For the finger frame, the portals and the hand signs, keep your hands a little inside the camera's picture.
• What it can and can't hear yet: the end of docs/how-it-works.md.

With Node.js (it's built with Node 24):

npm install
npm start          # run it
npm run dev        # run it with a debugging port (9333) for tools/cdp.mjs and tools/checks.js
npm run package    # build for the OS you're on: dist/Toaster-win32-x64, or dist/Toaster-darwin-universal

On a Mac, npm start compiles the Swift helpers (now playing, and faces) the first time, with Xcode's command line tools. npm run package:win and npm run package:mac build the other OS's app; the Mac app has to be built on a Mac. Each release's Mac app is built on GitHub's Macs (.github/workflows/mac.yml), signed ad hoc.

How it works inside, and the test songs it's checked against: docs/how-it-works.md.

Toaster is MIT licensed (LICENSE). It uses Google's MediaPipe (Apache 2.0) for the camera; THIRD-PARTY-NOTICES.txt lists everything it uses and the artists whose looks it's after. The code it writes is Strudel. Toaster is an independent project, not made by or affiliated with the Strudel project.