Docs: add MacOS passthrough to TODO.md

Author: Soddentrough

TODO.md

@@ -11,3 +11,16 @@ The idea will be to load this scene and use a ray tracing engine to light up the
 **Concerns:**
 *   Binary file size bloat.
 *   Computational intensity of a ray traced scene with dynamic lighting. Obviously only available on supported hardware. Must render very fast to maintain 120Hz.
+
+## MacOS Bitstream/Passthrough Implementation
+
+**Feature Request:**
+Implement native bitstream passthrough for macOS to support spatial surround formats (AC3, E-AC3) directly via HDMI/Optical.
+
+**Implementation Notes:**
+*   macOS relies on CoreAudio. To support bitstreaming, we must write a HAL (Hardware Abstraction Layer) implementation.
+*   Requires bypassing the macOS system mixer by seizing "Hog Mode" (`kAudioDevicePropertyHogMode`) on the audio device.
+*   Must explicitly set the device's physical stream format to `kAudioFormat60958AC3` (or similar IEC 61937 sub-formats) to tell the OS to send raw frames.
+
+**Concerns:**
+*   Apple Silicon Macs are heavily restricted regarding HDMI audio passthrough. High-bandwidth lossless formats like TrueHD and DTS-HD Master Audio are likely to be stripped or decoded natively and may require EDID spoofers.