From 04bbff47024acdc897388b026514d98910549239 Mon Sep 17 00:00:00 2001
From: Andreas Pehrson <apehrson@mozilla.com>
Date: Fri, 31 May 2024 01:41:40 +0200
Subject: [PATCH] Report 1 channel for builtin input devices

The builtin mic is always mono. Except when VPIO is live somewhere on
the system, as it is then 3, at least on modern MacBooks (with a mic
array). For this reason, and that mixing those 3 channels does not
result in good audio, we already force VPIO with the builtin mic. To
properly pass tests on a local machine with a builtin mic, and to have
clients not be fooled in a way resulting in us having to upmix input
audio, we override the builtin mic's reported channel count and always
report 1.
---
 src/backend/mod.rs | 27 +++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)

diff --git a/src/backend/mod.rs b/src/backend/mod.rs
index 79354774..c1183e89 100644
--- a/src/backend/mod.rs
+++ b/src/backend/mod.rs
@@ -1621,10 +1621,16 @@ fn get_channel_count(
     debug_assert_running_serially();
 
     let devstreams = get_device_streams(devid, devtype)?;
-    let mut count = 0;
+    let mut count: u32 = 0;
     for ds in devstreams {
-        if let Ok(format) = get_stream_virtual_format(ds.stream) {
-            count += format.mChannelsPerFrame;
+        if devtype == DeviceType::INPUT
+            && CoreStreamData::should_force_vpio_for_input_device(ds.device)
+        {
+            count += 1;
+        } else {
+            count += get_stream_virtual_format(ds.stream)
+                .map(|f| f.mChannelsPerFrame)
+                .unwrap_or(0);
         }
     }
     Ok(count)
@@ -3212,14 +3218,15 @@ impl<'ctx> CoreStreamData<'ctx> {
     }
 
     #[allow(non_upper_case_globals)]
-    fn should_force_vpio_for_input_device(&self, in_device: &device_info) -> bool {
-        assert!(in_device.id != kAudioObjectUnknown);
-        self.debug_assert_is_on_stream_queue();
-        match get_device_transport_type(in_device.id, DeviceType::INPUT) {
+    fn should_force_vpio_for_input_device(id: AudioDeviceID) -> bool {
+        assert!(id != kAudioObjectUnknown);
+        debug_assert_running_serially();
+        match get_device_transport_type(id, DeviceType::INPUT) {
             Ok(kAudioDeviceTransportTypeBuiltIn) => {
                 cubeb_log!(
-                    "Forcing VPIO because input device is built in, and its volume \
-                     is known to be very low without VPIO whenever VPIO is hooked up to it elsewhere."
+                    "Input device {} is on the VPIO force list because it is built in, \
+                     and its volume is known to be very low without VPIO whenever VPIO \
+                     is hooked up to it elsewhere."
                 );
                 true
             }
@@ -3296,7 +3303,7 @@ impl<'ctx> CoreStreamData<'ctx> {
                 .input_stream_params
                 .prefs()
                 .contains(StreamPrefs::VOICE)
-                || self.should_force_vpio_for_input_device(&self.input_device))
+                || CoreStreamData::should_force_vpio_for_input_device(self.input_device.id))
             && !self.should_block_vpio_for_device_pair(&self.input_device, &self.output_device)
             && macos_kernel_major_version() != Ok(MACOS_KERNEL_MAJOR_VERSION_MONTEREY);