@bun-win32/mmdevapi

Zero-dependency, zero-overhead Win32 Mmdevapi bindings for Bun on Windows.

Overview

@bun-win32/mmdevapi exposes the mmdevapi.dll exports using Bun's FFI. It provides a single class, Mmdevapi, which lazily binds native symbols on first use. You can optionally preload a subset or all symbols up-front via Preload().

The bindings are strongly typed for a smooth DX in TypeScript.

Features

• Bun-first ergonomics on Windows 10/11.
• Direct FFI to mmdevapi.dll (MMDevice / Core Audio endpoint enumeration and WASAPI activation).
• In-source docs in structs/Mmdevapi.ts with links to Microsoft Docs.
• Lazy binding on first call; optional eager preload (Mmdevapi.Preload()).
• No wrapper overhead; calls map 1:1 to native APIs.
• Strongly-typed Win32 aliases (see types/Mmdevapi.ts).

Requirements

• Bun runtime
• Windows 10 or later

Installation

bun add @bun-win32/mmdevapi

Quick Start

import { ptr } from 'bun:ffi';

import Mmdevapi, { CLSID_MMDeviceEnumerator, IID_IMMDeviceEnumerator } from '@bun-win32/mmdevapi';

function guidBytes(guid: string): Buffer {
  const [, d1, d2, d3, d4High, d4Low] = /^([0-9a-f]{8})-([0-9a-f]{4})-([0-9a-f]{4})-([0-9a-f]{4})-([0-9a-f]{12})$/i.exec(guid)!;
  const buffer = Buffer.alloc(16);
  buffer.writeUInt32LE(parseInt(d1, 16), 0);
  buffer.writeUInt16LE(parseInt(d2, 16), 4);
  buffer.writeUInt16LE(parseInt(d3, 16), 6);
  const data4 = `${d4High}${d4Low}`;
  for (let i = 0; i < 8; i += 1) buffer[8 + i] = parseInt(data4.slice(i * 2, i * 2 + 2), 16);
  return buffer;
}

// Resolve the MMDevice class factory without CoCreateInstance.
const clsid = guidBytes(CLSID_MMDeviceEnumerator);
const iidFactory = guidBytes('00000001-0000-0000-c000-000000000046'); // IID_IClassFactory
const factoryOut = Buffer.alloc(8);

const hr = Mmdevapi.DllGetClassObject(ptr(clsid), ptr(iidFactory), ptr(factoryOut));
console.log('DllGetClassObject →', `0x${(hr >>> 0).toString(16).padStart(8, '0')}`);
console.log('IClassFactory *   →', `0x${factoryOut.readBigUInt64LE(0).toString(16).padStart(16, '0')}`);

// Preload for hot paths (optional):
Mmdevapi.Preload(['DllGetClassObject', 'ActivateAudioInterfaceAsync']);

[!NOTE] AI agents: see AI.md for the package binding contract and source-navigation guidance. It explains how to use the package without scanning the entire implementation.

Examples

Run the included examples:

bun run example:audio-device-radar
bun run example:mmdevapi-factory-probe

Notes

• Either rely on lazy binding or call Mmdevapi.Preload().
• Windows only. Bun runtime required.
• SAL types & naming: nullability is in the type — Optional<T> (formally optional, SAL _*opt_) and Nullable<T> (plain [in]/[out] the docs say can be NULL), the null sentinel derived from T (null for pointers LP*/P*, 0n for handles/by-value addresses); direction is in the parameter name — _out (_Out_), _in_out (_Inout_), _In_ bare. See AI.md and the repo AGENTS.md.