djay Pro Bridge

A macOS tool that reads real-time deck state from Algoriddim djay Pro using the macOS Accessibility API. This only supports djay Pro on Mac.

Table of Contents

• djay Pro Bridge
  • Table of Contents
  • Why
  • Setup
    • Dump
  • Discovering More Accessibility Elements
  • Time Display
    • Time availability
  • Available Data Per Deck
    • Readable Values
    • Action-Only Buttons (WIP)
    • Other (not per-deck)
  • Limitations
  • References
  • License

Why

djay Pro doesn't expose deck metadata (key, title, artist, BPM) to external software. There's no MIDI output for these values, no network protocol like Pioneer's Pro DJ Link, or any external software such as ShowKontrol for djay Pro.

The first idea was to read djay Pro's memory directly, but this was quickly scrapped — macOS's System Integrity Protection (SIP) blocks cross-process memory reading, and disabling it would compromise system security. This was not worth it for me.

The next idea was polling djay Pro's song database and tracking MIDI input to reconstruct state externally, but this would get out of sync fast — especially when the DJ shifts keys or loads tracks in ways the external tracker can't anticipate.

The breakthrough (with some help from Claude) was discovering that macOS has Accessibility APIs that let you read text and values directly from any app's UI. djay Pro, being a Mac-native app, exposes a rich accessibility tree with labeled elements for every deck — key, title, artist, and more. The only way to get this data out without compromising system security is through the macOS Accessibility API, which reads the live UI state directly — including any key shifts or changes the DJ makes in real time.

Setup

1. Xcode Command Line Tools must be installed.

2. Grant Accessibility permission to whatever runs the tool (Terminal, iTerm2, VSCode, etc.).

3. Run djay Pro.

4. Run the reader:

   swift run Reader

The reader shows a live TUI display of deck state:

djay Pro Bridge

Deck 1 ▶
  What It Sounds Like (AWAIAN Future House Remix)
  HUNTR/X, EJAE, AUDREY NUNA, REI AMI & KPop Demon Hunters Cast, AWAIAN
  Key: e
  BPM: 124.0 (0.0%) | 01:35.~4 / -05:05.~6

Deck 2 ⏸
  My Way (AWAIAN Remix)
  KATSEYE, AWAIAN
  Key: e flat
  BPM: 128.0 (0.0%) | 00:00.~0 / -02:58.~0

Options:

swift run Reader --interval 100  # render interval in ms (default 33, ~30fps)
swift run Reader --log           # scrolling log output instead of TUI

The reader uses two threads: a background thread polls djay Pro's accessibility tree continuously (estimated ~8fps, limited by the cost of the accessibility tree walk), while the main thread renders at the --interval rate. The higher render rate allows smooth interpolated deck timestamps, which is important for timecode output that can be added later.

Dump

The dump tool outputs all discovered accessibility elements as JSON:

swift run Dump                # prints JSON to stdout
swift run Dump > elements.json  # save to file

Discovering More Accessibility Elements

Note: This section requires the full Xcode app installed (not just Command Line Tools).

djay Pro exposes a rich accessibility tree — far more than just key and title. To explore what's available:

1. Open Accessibility Inspector — in Xcode, go to Xcode → Open Developer Tool → Accessibility Inspector.

2. In Accessibility Inspector, select your Mac as the target device from the dropdown in the top left.

3. Click the crosshair/target button (or press ⌥Space) to enable the inspection pointer.

4. Hover over any element in djay Pro's UI. The inspector will show:

   • Label (AXDescription) — the element's accessible name, e.g., "Key, Deck 1"
   • Value — the current displayed value, e.g., "c minor"
   • Role — the element type (AXButton, AXStaticText, etc.)
   • Parent/Children — the full hierarchy

5. Use the hierarchy view (the tree icon in the toolbar) to browse the full element tree without hovering. The structure is:

   djay Pro (ARApplication)
     └─ djay Pro (standard window) [NSWindow]
        └─ Decks (group) [ARMacMetalView]
           ├─ Title, Deck 1 (text)
           ├─ Artist, Deck 1 (text)
           ├─ Key, Deck 1 (button)
           ├─ Remaining time, Deck 1 (button)
           ├─ 124.0, Deck 1 (button)             ← BPM (value-as-label)
           ├─ 0.0%, Deck 1 (button)              ← BPM % (value-as-label)
           ├─ Play / Pause, Deck 1 (button)
           ├─ Waveform, Deck 1 (unknown)
           ├─ ...
           └─ [Deck 2 elements follow the same pattern]
   

Element labels follow two patterns:

1. Standard: "PropertyName, Deck N" — the label names the property, the value holds the data. E.g. "Key, Deck 1" has value "e".
2. Value-as-label: The label itself IS the data. E.g. "124.0, Deck 1" is the BPM number, "0.0%, Deck 1" is the BPM percentage. The element's value field holds something else (slider position).

Time Display

The reader shows elapsed and remaining time with sub-second precision (one decimal place). Since the Accessibility API only provides whole-second MM:SS values, the fractional second is interpolated between polls using wall-clock time. Interpolated values are shown with a ~ prefix (e.g. 01:35.~4) to indicate they are approximate.

The interpolator accounts for tempo changes — if BPM% is +3.2%, time advances 3.2% faster than wall clock. On every poll, the interpolator snaps to reality: if the new AX time differs from the prediction by more than ~1 second (e.g. looping, or track jumps), it resets instantly rather than trying to smooth the difference.

Time availability

Which time values are visible depends on djay Pro's current view:

View	Elapsed	Remaining
Jog view enabled	Yes	Yes
Timer (next to key value in app) showing remaining time	No	Yes
Timer (next to key value in app) showing elapsed time	Yes	No

Note: the timer toggle (next to the key value in the app) to show remaining or elapsed time is per deck — it is not global.

When a time value isn't available, the reader shows --:--.~- as a placeholder with a hint to change the view.

Available Data Per Deck

Everything below is read per deck (Deck 1, 2, etc.) from the accessibility tree.

Note: These may highly vary or depend on the specific view mode that is showing in djay Pro. This is due to the accessibility tree changing based on the view mode. These are the initial ones I found with my current configuration.

Readable Values

Element	Role	Example Value	Notes
Title	AXStaticText	What It Sounds Like (AWAIAN Future House Remix)
Artist	AXStaticText	HUNTR/X
Key	AXButton	f minor
BPM	AXButton/AXStaticText	126.0	Value-as-label pattern
BPM %	AXButton/AXStaticText	0.0%, +7.3%	Value-as-label pattern
Elapsed time	AXButton/AXStaticText	01:35	Availability depends on view (confirmed, see Time availability section)
Remaining time	AXButton/AXStaticText	-05:05	Availability depends on view (confirmed, see Time availability section)
Play / Pause	AXButton	Active / nil	Active = playing
Key Lock on-off	AXButton	Active / nil
Quantize	AXButton	Active / nil
Loop	AXButton	4 Beats	Current loop size
DVS	AXButton	INT
Skip Forward/Backward	AXButton	16 Beats	Current skip size (not confirmed, but this may depend on whether the beat jump buttons are shown — the buttons configurable next to the crossfader in non-hardware mode view)
Tempo	AXSlider	0%	Slider position, not BPM
Filter	AXSlider	50%
High / Mid / Low EQ	AXSlider	50%
Gain	AXSlider	42%
Line volume	AXSlider	100%
FX Parameter	AXSlider	80%	Per FX slot (1-3)
FX Wet/dry	AXSlider	100%	Per FX slot (1-3)
FX Parameter name	AXStaticText	0 BEAT	Per FX slot (1-3)

Action-Only Buttons (WIP)

These AXButton elements had no value in our test dumps, but some may expose state (e.g. Active) when engaged — needs further testing. For triggering actions, MIDI mapping is recommended.

Sync, CUE, Set start point, Jump to start point, Loop Half, Loop Double, Pitch Bend +/-, Key shift, Mute until cue, Precue, EQ Type, Edit grid, Waveform options, Neural Mix Solo (all channels), Instant FX, Instrumental, Percussive, Acapella, Tonal, FX Enable/Sidechain/Riser/Time Travel, Slice options, Slice repeat, Pitch Cue, Cue Points, Cuepoint Range, Looping, Shows quantize options.

Other (not per-deck)

Element	Role	Example Value
Crossfader	AXSlider	50%
External Mixer	AXButton	—

Limitations

• Play state detection delay (~700ms): When a deck is paused, djay Pro's play/pause button flashes in the accessibility tree — rapidly alternating between "Active" and nil. To avoid false play detection, the reader debounces the paused-to-playing transition, requiring the button to report "Active" consistently for ~700ms before the deck is considered playing. Playing-to-paused detection is immediate.
• View-dependent data availability: The accessibility tree changes based on djay Pro's current view mode. Some elements (elapsed/remaining time, beat jump buttons, etc.) may only be available in certain views.

References

The main deck algorithm is adapted from Pioneer DJ's sync master behavior, informed by:

• AlphaTheta Help Center: "I don't understand the conditions by which the sync master switches."
• Deep Symmetry DJ Link Ecosystem Analysis: Sync and Tempo Master

License

MIT