Merge pull request arduino-libraries#7 from arduino-libraries/i2s-mono-support

Add mono input support for I2S playback

Author: agdl

src/AudioOut.cpp

@@ -62,6 +62,46 @@ void AudioOut::endInput(AudioIn* input)
   return input->end();
 }
 
+void AudioOut::monoToStereo(void* buffer, size_t size, int bitsPerSample)
+{
+  int samples = size / (bitsPerSample / 8);
+
+  if (bitsPerSample == 8) {
+    uint8_t* s = &((uint8_t*)buffer)[samples - 1];
+    uint8_t* d = &((uint8_t*)buffer)[samples * 2 - 1];
+
+    for (int i = 0; i < samples; i++) {
+      *d = *s;
+      d--;
+      *d = *s;
+      d--;
+      s--;
+    }
+  } else if (bitsPerSample == 16) {
+    int16_t* s = &((int16_t*)buffer)[samples - 1];
+    int16_t* d = &((int16_t*)buffer)[samples * 2 - 1];
+
+    for (int i = 0; i < samples; i++) {
+      *d = *s;
+      d--;
+      *d = *s;
+      d--;
+      s--;
+    }
+  } else if (bitsPerSample == 32) {
+    int32_t* s = &((int32_t*)buffer)[samples - 1];
+    int32_t* d = &((int32_t*)buffer)[samples * 2 - 1];
+
+    for (int i = 0; i < samples; i++) {
+      *d = *s;
+      d--;
+      *d = *s;
+      d--;
+      s--;
+    }
+  }
+}
+
 void AudioOut::adjustVolume(void* buffer, size_t size, int bitsPerSample)
 {
   int samples = size / (bitsPerSample / 8);

src/AudioOut.h

@@ -46,6 +46,8 @@ class AudioOut
   int resetInput(AudioIn* input);
   void endInput(AudioIn* input);
 
+  void monoToStereo(void* buffer, size_t size, int bitsPerSample);
+
 private:
   void adjustVolume(void* buffer, size_t size, int bitsPerSample);
 

src/AudioOutI2S.cpp

@@ -41,7 +41,7 @@ int AudioOutI2SClass::canPlay(AudioIn& input)
     return 0;
   }
 
-  if (channels != 2) {
+  if (channels != 1 && channels != 2) {
     return 0;
   }
 
@@ -146,9 +146,16 @@ void AudioOutI2SClass::onTransmit()
     return;
   }
 
+  int channels = _input->channels();
+
   uint8_t data[512];
+  size_t length = sizeof(data);
+
+  if (channels == 1) {
+    length /= 2;
+  }
 
-  int n = readInput(_input, data, sizeof(data));
+  int n = readInput(_input, data, length);
 
   if (n == 0) {
     if (!_loop) {
@@ -164,7 +171,13 @@ void AudioOutI2SClass::onTransmit()
     }
 
     // read the input (again)
-    n = readInput(_input, data, sizeof(data));
+    n = readInput(_input, data, length);
+  }
+
+  if (channels == 1) {
+    monoToStereo(data, n, _input->bitsPerSample());
+
+    n *= 2;
   }
 
   I2S.write(data, n);