Multi device support: moved DSPDeviceEngine start/stop actions and status from main window to each source plugin GUI

sdrbase/dsp/dspengine.cpp

@@ -20,7 +20,8 @@
 #include "dsp/dspengine.h"
 
 DSPEngine::DSPEngine() :
-	m_audioSampleRate(48000) // Use default output device at 48 kHz
+	m_audioSampleRate(48000), // Use default output device at 48 kHz
+	m_audioUsageCount(0)
 {
     m_deviceEngines.push_back(new DSPDeviceEngine(0)); // TODO: multi device support
 	m_dvSerialSupport = false;
@@ -86,6 +87,30 @@ bool DSPEngine::startAcquisition(uint deviceIndex)
 	return started;
 }
 
+void DSPEngine::startAudio()
+{
+    if (m_audioUsageCount == 0)
+    {
+        m_audioOutput.start(-1, m_audioSampleRate);
+        m_audioSampleRate = m_audioOutput.getRate(); // update with actual rate
+    }
+
+    m_audioUsageCount++;
+}
+
+void DSPEngine::stopAudio()
+{
+    if (m_audioUsageCount > 0)
+    {
+        m_audioUsageCount--;
+
+        if (m_audioUsageCount == 0)
+        {
+            m_audioOutput.stop();
+        }
+    }
+}
+
 void DSPEngine::stopAcquistion(uint deviceIndex)
 {
 	qDebug("DSPEngine::stopAcquistion(%d)", deviceIndex);