EffectDeck

Effects for any player on your phone

Free and open source under the MIT license.

Website: effectdeck.nemut.ai

 

An independent project. EffectDeck is built by nemut.ai. It is not affiliated with, endorsed by, or supported by EffeTune or its author (Frieve-A / Yoshiyuki Kobayashi). It bundles EffeTune's DSP core under the MIT license and says so.

Send anything about this app to nemut.ai, not to EffeTune. Do not open issues about it on the EffeTune repository.

Effects for any player on your phone. Anything with a transport in Control Center, the Now Playing kind, goes through the chain: it takes that audio, runs it through EffeTune's effects, and plays it on whatever was the output before you picked EffectDeck: the speaker, wired headphones, AirPods. No virtual cable, no input device to configure. Pick EffectDeck as the output in Control Center and that is the whole setup.

Spotify / a podcast app / Safari
  ↓ pick EffectDeck as the output in Control Center
extension (Media Device Extension)   ← receives
  ↓ 127.0.0.1:47101
app                                  ← runs EffeTune's DSP
  ↓
the output you had before (speaker / headphones / AirPods)

If it says Unable to Connect

Almost always Spotify with Canvas on. Canvas is the short looping video behind some tracks. While one plays, the session counts as video output, so iOS sends the route to AirPlay instead of here, finds no receiver, and puts it back where it was. A track with Canvas enabled cannot connect to EffectDeck, and Spotify does not have to be on screen for it. Turn Canvas off in Spotify's settings, then restart Spotify.

Spotify sometimes cannot connect even on a track without a Canvas: when Spotify has a video (such as a Canvas) loaded, iOS treats it as playing video, even while paused. Restart Spotify, then connect to EffectDeck again.

Playing a YouTube video may disconnect EffectDeck, depending on YouTube's playback state. Restart YouTube, then connect to EffectDeck again; the same video usually connects.

Otherwise, try these in order:

1. Restart the player app
2. Restart EffectDeck
3. Restart the iPhone

The decision is made by iOS. None of the arguments MediaOutputDevice takes are read when it is made, so there is nothing on this side to set.

The iOS 27 Media Device Extension

iOS 27 added MediaDevice.framework, which lets an app present itself as an output device the way an AirPlay speaker does. EffectDeck advertises itself that way, and once it is picked the system hands it the audio as samples.

It runs as two processes. The extension advertises the device and receives the audio; the app processes it and plays it. They are split because the extension's sandbox denies files, shared memory and bind. Outbound connections are allowed, so the audio goes over a single TCP connection to the app. It ships as one app, and the user installs one app.

Signing the app itself with com.apple.developer.media-device-extension stops it from opening an AVAudioSession: every category fails with '!pla'. The check only looks at whether the entitlement's array is empty, so the app carries an empty array and the extension carries the protocol identifier. That also gets past App Store Connect's ITMS-91183.

To build an app like this, start from ios27-media-device-passthrough: the same two processes in a handful of files, with a low-pass filter where EffectDeck has its effects. It is MIT-0, so you can copy it without keeping the copyright notice.

Writing a JSFX for it

EffectDeck hosts single-file audio JSFX through the portable EEL2 interpreter. JSFX.md is the contract: what is supported, what is deliberately absent, the rules that reject a file outright, and the resource limits. It is written to be handed to a language model as-is — the top section states the requirements in the order they are usually violated, and there is a checklist to run a generated script against before you try to import it.

In the app, Write JSFX with ChatGPT (Plugins, or the Import JSFX menu) opens ChatGPT with a short request that names the EffectDeck and EffeTune DSP versions, points it at JSFX.md, and asks what you want to build. Import the file it returns with Import JSFX → From Files, or copy the script and use From Clipboard. Use a paid ChatGPT plan: it reads the linked file and reasons through the code, while the free tier may skip the link and miss the rules.

The short version: one file, no import or include(), no filesystem, no MIDI, desc: first, and no JIT — so keep @sample cheap.

It describes only the differences, not the language. For JSFX itself, read REAPER's JS: Programming Reference and JoepVanlier/ysfx, which is the interpreter embedded here.

Build with ChatGPT… (the top of the Effects list in Available Effects) opens ChatGPT the same way, for a chain of the built-in effects instead of a script. CHAIN.md is its contract; the effect names and keys it points to are generated for each EffeTune DSP version under chain/. Bring the chain back with Import from clipboard in Presets, or tap the link ChatGPT gives when it can run code.

Building

git clone https://github.com/satomasahiro2005/EffectDeck
cd EffectDeck
git submodule update --init Vendor/effetune Vendor/ysfx
bash Scripts/build.sh          # build and install on the attached device

Leave out --recursive: ysfx's own submodules are not used. Keep the effetune submodule's full history, not --depth 1, because Tools/gen_version.py reads its dsp-v* tag.

To open it in Xcode, generate first. The .xcodeproj is not tracked; project.yml is the source.

bash Scripts/setup.sh
open EffeTuneLive.xcodeproj

You need:

• macOS with Xcode 27 or later
• A device running iOS 27 or later. The extension needs iOS 27, so no audio flows in the simulator
• Apple Developer Program membership (set DEVELOPMENT_TEAM in project.yml to yours)
• xcodegen and python3 3.10+ from Homebrew

The script finds the attached device. With more than one, use DEV_ID=<UDID> bash Scripts/build.sh. The log goes to build.log; look for BUILD SUCCEEDED there.

Run Scripts/build.sh from Terminal in the Mac's own login session, not over SSH. Over SSH codesign cannot reach the keychain, and signing the extension fails with errSecInternalComponent. The compile still succeeds, so an unsigned out/EffectDeck.app appears and the install then fails with "not a valid bundle".

Building under your own Apple ID

Set DEVELOPMENT_TEAM in project.yml to your team, change the identifiers below to your own, and create them in the Apple Developer portal.

What	Today's value	Where it is written
App ID for the app	ai.nemut.effetune	project.yml (EffeTuneLive target)
App ID for the Media Device extension	ai.nemut.effetune.extension	project.yml (EffeTuneLiveExtension)
App ID for the share extension	ai.nemut.effetune.share	project.yml (EffectDeckShare)
Media Device Sharing Extension identifier	media-device-protocol.ai.nemut.effetune	Sources/Extension/Extension.entitlements, UTExportedTypeDeclarations in Sources/Extension/Info.plist, and kProtocolID in Sources/Extension/EffeTuneLiveExtension.swift
App Group	group.ai.nemut.effetune	all three .entitlements files and ETShareInbox.group in Sources/EffeTuneLive/DSP/ETShareInbox.swift
iCloud key-value storage	follows the app's bundle ID	Sources/EffeTuneLive/EffeTuneLive.entitlements
Associated Domains	applinks:effectdeck.nemut.ai	Sources/EffeTuneLive/EffeTuneLive.entitlements

• The Media Device Sharing Extension identifier is made under Identifiers > new. There is no review. The entitlement value must be an array with one element; a bare string stops the extension from launching. Change all three places together: the extension offers kProtocolID as its protocol type, and it must match the entitlement.
• Tools/check_release_binary.py checks a release archive against today's values (BUNDLES, APP_GROUP and APPLINKS at the top of the file). Change them there too if you use it.
• The app itself carries com.apple.developer.media-device-extension as an empty array. Leave it empty (see The iOS 27 Media Device Extension above).
• Enable App Groups on all three App IDs, iCloud (key-value storage only) on the app, and Associated Domains on the app.
• Share links only open the app if the domain serves an apple-app-site-association that names your app. site/ serves it for effectdeck.nemut.ai. Without a domain of your own, remove the Associated Domains key; links then open in the browser.

Working on the code

Names

The app is EffectDeck. The project, the targets and many files still carry its first name, EffeTune Live: EffeTuneLive.xcodeproj, the EffeTuneLive app target (product name EffectDeck), EffeTuneLiveExtension, Sources/EffeTuneLive. They are the same app. "EffeTune" alone means the upstream project in Vendor/effetune.

What is pinned and patched

Path	What it is
Vendor/effetune	EffeTune, pinned by the submodule. Its dsp/ is the audio engine
Vendor/ysfx	ysfx, the JSFX interpreter, pinned to 5c3452fe. Scripts/setup.sh refuses another revision
Patches/abi-begin-ptr.diff	Adds et_instance_asset_begin_ptr, a 64-bit staging pointer. Without it the seven effects that load data (IR Reverb and the ones designed in the app, such as Room EQ) pass audio through silently
Patches/effetune-external-*.diff	Let AUv3 and JSFX run as nodes inside the EffeTune chain (docs/external-processor.md)
Patches/ysfx-effectdeck-ios.diff	The iOS sandbox for ysfx and fixes taken from upstream WDL
Patches/ysfx-effectdeck-ios.old.diff	The previous ysfx patch. Never applied; setup.sh uses it to take the old version off a copied tree

Scripts/setup.sh applies the patches to the submodule working trees, regenerates the effect catalog and presets from Vendor/effetune, and runs xcodegen. The patched submodule trees are never committed; the patches are. docs/ lists the design documents and notes.

Tests

None of these need a device or a paid account. CONTRIBUTING.md has the exact commands.

Suite	Runs on	Command
Logic tests (all of Tests/Unit, JSFX included)	Mac with Xcode, simulator	bash Scripts/test.sh, or the Logic scheme in Xcode
The Foundation-only part of the Logic tests	Linux or WSL with Swift	bash Tests/Linux/run.sh --name local
Native C tests (Tests/Native)	Linux, macOS or WSL with CMake	cd Tests/Native && cmake --preset asan && cmake --build --preset asan && ctest --preset asan
Website (site/)	Node 22	cd site && npm ci && npm test
Generators and checks (Tools/, Tests/Tools)	Python 3.10+ and Node 22, any OS	python3 -m unittest discover -s Tests/Tools
UI tests (Tests/UI)	Mac with Xcode, simulator	bash Scripts/uitest.sh MenuProbe (one class; see CONTRIBUTING)

GitHub Actions runs all of them but the UI tests, and checks that generated files are up to date, on every push to main and every pull request (CI).

Launch arguments

For the simulator and for debugging. They are read from UserDefaults, so they are passed as -Name value to xcrun simctl launch, xcrun devicectl device process launch or an XCUITest launchArguments. The icon on the home screen passes none.

Argument	What it does
-ETSeed <name>	Starts with a prepared chain instead of the saved one, every card open. none, peq, compressor, saturation, meter, spectrum, peq-spectrum, chain, store, analyzers4; a factory preset by short name (vinyl, karaoke, analyzers, live, tube, bbe, fmradio); demo in Debug builds; anything else is read as plugin type names separated by commas
-ETMock 1	Feeds a generated test signal, so meters and graphs move without the extension
-ETWidth <pt>	With -ETSeed, the width of the one-column chain, so screenshots taken on iPad look like a phone. Default 393; 0 keeps the device width
-ETLayout wide	With -ETSeed, keeps the two-column iPad layout instead of one column
-ETCollapsed 1	With -ETSeed, starts with every card closed. A card with a graph still shows the graph
-ETSheet <name>	Opens a sheet at launch: picker, settings, routing, presets, ir, tips
-ETAutoExpand 1, -ETAutoExpandIndex <n>	Taps an effect once, 4 seconds after launch, to record the animation. A tap moves the card one step (open → graph only → folded → open), so it opens only a folded card, and a card that -ETSeed opened keeps only its graph. The first effect by default; n counts from 0 and skips Sections
-ETDebugBlocks 1	Tints each Section block to check grouping
-ETDiag 1	Adds a hidden diag text with the active node count and chain length, for UI tests
-ETConsole 1	Also prints the diagnostic log to stdout, for devicectl ... --console
-ETNowPlaying on|off|first	Whether the app claims Now Playing (default off). Debug builds save it to UserDefaults and keep it on later launches until another value is passed; Release builds use it for that launch only
-ETProbe 1	Shows the reorder probe screen instead of the app
-pref.<key> <value>	Overrides a setting for that launch, for example -pref.power balanced

License

Free and open source under the MIT license. Everything bundled in the app is open source too; NOTICE.md lists each part and its license.