CoreAudio: fix supported channel count.

We were using the number of channels actually used by audio devices as
the maximum channel count. This is wrong as CoreAudio can automatically
split or merge channels in order to accommodate the device.
We now assume all channel configurations are valid.

Task-number: QTBUG-37956
Change-Id: Ia8e8bbea8543caa7fecda305be74a2953b92fd25
Reviewed-by: Andy Nichols <andy.nichols@digia.com>

3 files changed, 6 insertions, 43 deletions

diff --git a/src/plugins/coreaudio/coreaudiodeviceinfo.mm b/src/plugins/coreaudio/coreaudiodeviceinfo.mm
index 56765cafd..ac41a310c 100644
--- a/src/plugins/coreaudio/coreaudiodeviceinfo.mm
+++ b/src/plugins/coreaudio/coreaudiodeviceinfo.mm
@@ -196,38 +196,14 @@ QList<int> CoreAudioDeviceInfo::supportedSampleRates()
 
 QList<int> CoreAudioDeviceInfo::supportedChannelCounts()
 {
-    QList<int> supportedChannels;
-    int maxChannels = 0;
+    static QList<int> supportedChannels;
 
-#if defined(Q_OS_OSX)
-    UInt32 propSize = 0;
-    AudioObjectPropertyScope scope = m_mode == QAudio::AudioInput ? kAudioDevicePropertyScopeInput : kAudioDevicePropertyScopeOutput;
-    AudioObjectPropertyAddress streamConfigurationPropertyAddress = { kAudioDevicePropertyStreamConfiguration,
-                                                                      scope,
-                                                                      kAudioObjectPropertyElementMaster };
-
-    if (AudioObjectGetPropertyDataSize(m_deviceId, &streamConfigurationPropertyAddress, 0, NULL, &propSize) == noErr) {
-        AudioBufferList* audioBufferList = static_cast<AudioBufferList*>(malloc(propSize));
-
-        if (audioBufferList != 0) {
-            if (AudioObjectGetPropertyData(m_deviceId, &streamConfigurationPropertyAddress, 0, NULL, &propSize, audioBufferList) == noErr) {
-                for (int i = 0; i < int(audioBufferList->mNumberBuffers); ++i)
-                    maxChannels += audioBufferList->mBuffers[i].mNumberChannels;
-            }
-
-            free(audioBufferList);
-        }
+    if (supportedChannels.isEmpty()) {
+        // If the number of channels is not supported by an audio device, Core Audio will
+        // automatically convert the audio data.
+        for (int i = 1; i <= 16; ++i)
+            supportedChannels.append(i);
     }
-#else //iOS
-    if (m_mode == QAudio::AudioInput)
-        maxChannels = CoreAudioSessionManager::instance().inputChannelCount();
-    else if (m_mode == QAudio::AudioOutput)
-        maxChannels = CoreAudioSessionManager::instance().outputChannelCount();
-#endif
-
-    // Assume all channel configurations are supported up to the maximum number of channels
-    for (int i = 1; i <= maxChannels; ++i)
-        supportedChannels.append(i);
 
     return supportedChannels;
 }
diff --git a/src/plugins/coreaudio/coreaudiosessionmanager.h b/src/plugins/coreaudio/coreaudiosessionmanager.h
index 61d8967b1..26f8fee09 100644
--- a/src/plugins/coreaudio/coreaudiosessionmanager.h
+++ b/src/plugins/coreaudio/coreaudiosessionmanager.h
@@ -92,9 +92,6 @@ public:
     QList<QByteArray> inputDevices();
     QList<QByteArray> outputDevices();
 
-    int inputChannelCount();
-    int outputChannelCount();
-
     float currentIOBufferDuration();
     float preferredSampleRate();
 
diff --git a/src/plugins/coreaudio/coreaudiosessionmanager.mm b/src/plugins/coreaudio/coreaudiosessionmanager.mm
index 0e795e786..04c8b6ed4 100644
--- a/src/plugins/coreaudio/coreaudiosessionmanager.mm
+++ b/src/plugins/coreaudio/coreaudiosessionmanager.mm
@@ -377,16 +377,6 @@ QList<QByteArray> CoreAudioSessionManager::outputDevices()
     return outputDevices;
 }
 
-int CoreAudioSessionManager::inputChannelCount()
-{
-    return [[m_sessionObserver audioSession] inputNumberOfChannels];
-}
-
-int CoreAudioSessionManager::outputChannelCount()
-{
-    return [[m_sessionObserver audioSession] outputNumberOfChannels];
-}
-
 float CoreAudioSessionManager::currentIOBufferDuration()
 {
     return [[m_sessionObserver audioSession] IOBufferDuration];