In AudioMonitor convertBuffer - the method that resamples the audio data to 48000 Hz - if TPCircularBufferProduceBytes indicates an error, it is probably due to a buffer overrun about to occur because the ring buffer space is depleted (possibly due to missed TPCircularBufferConsume getting missed somewhere?).

When the buffer overrun situation is detected, the method will clear the circular buffer and call TPCircularBufferProduceBytes to try to write to the buffer again.  This seems to work, although it is not the recommended practice.

Author: dsward2

AudioMonitor/AudioMonitor/AudioMonitor.mm

@@ -32,10 +32,6 @@
 #define kAudioQueueSampleRate 48000
 
 #define kInputPacketLength sizeof(SInt16)
-//#define kInputBufferLength (kInputMaxPackets * kInputPacketLength)
-
-//#define kOutputPacketLength sizeof(SInt16)
-//#define kOutputBufferLength (kInputMaxPackets * kOutputPacketLength)
 
 #define kAudioQueueBufferSize (kInputMaxPackets * sizeof(SInt16) * 2)
 
@@ -85,7 +81,6 @@ - (void)runInputBufferOnThread
     NSTimeInterval lastReadTime = [NSDate timeIntervalSinceReferenceDate] + 20;
     NSTimeInterval nextTimeoutReportInterval = 5;
 
-    //int32_t circularBufferLength = 512 * 1024;
     int32_t circularBufferLength = 256 * 1024;
     TPCircularBufferInit(&inputCircularBuffer, circularBufferLength);
 
@@ -141,21 +136,18 @@ - (void)runInputBufferOnThread
 
                         // copy RTL-SDR LPCM data to a circular buffer to be used as input for AudioConverter process
 
-                        int32_t space;
-                        void *ptr = TPCircularBufferHead(&inputCircularBuffer, &space);
-                        //NSLog(@"AudioMonitor runInputBufferOnThread Produce, bytesAvailableCount=%u, space = %d, head = %p", bytesAvailableCount, space, ptr);
+                        //int32_t space;
+                        //void *ptr = TPCircularBufferHead(&inputCircularBuffer, &space);   // for NSLog below
 
                         bool produceBytesResult = TPCircularBufferProduceBytes(&inputCircularBuffer, rtlsdrBuffer, bytesAvailableCount);
 
                         if (produceBytesResult == false)
                         {
                             TPCircularBufferClear(&inputCircularBuffer);
 
-                            NSLog(@"AudioMonitor runInputBufferOnThread Produce, bytesAvailableCount=%u, space = %d, head = %p", bytesAvailableCount, space, ptr);
+                            //NSLog(@"AudioMonitor runInputBufferOnThread Produce, bytesAvailableCount=%u, space = %d, head = %p", bytesAvailableCount, space, ptr);
                             NSLog(@"AudioMonitor runInputBufferOnThread - produce bytes failed, bytesAvailableCount = %d", bytesAvailableCount);
                         }
-                        
-                        //fwrite(rtlsdrBuffer, 1, bytesAvailableCount, stdout); // also write to stdout at original sampling rate, for sox, etc.
                     }
 
                     free(rtlsdrBuffer);
@@ -184,9 +176,6 @@ - (void)runInputBufferOnThread
 
         packetIndex++;
     }
-
-    //NSLog(@"AudioMonitor exit");
-    //fprintf(stderr, "AudioMonitor exit\n");
 }
 
 
@@ -203,7 +192,6 @@ - (void)runAudioConverterOnThread
     NSTimeInterval lastReadTime = [NSDate timeIntervalSinceReferenceDate] + 20;
     NSTimeInterval nextTimeoutReportInterval = 5;
 
-    //int32_t circularBufferLength = 256 * 1024;
     int32_t circularBufferLength = 128 * 1024;
     TPCircularBufferInit(&audioConverterCircularBuffer, circularBufferLength);
 
@@ -227,10 +215,6 @@ - (void)runAudioConverterOnThread
 
         if( bytesAvailableCount <= 0)
         {
-            //[NSThread sleepForTimeInterval:0.01f];
-
-            //TPCircularBufferClear(&inputCircularBuffer);
-
             usleep(1000);
         }
         else
@@ -242,18 +226,11 @@ - (void)runAudioConverterOnThread
 
                 //NSLog(@"AudioMonitor sending data, length=%ld", bytesAvailableCount);
 
-                //if (self.volume > 0.0f)
-                //{
-                //    [self convertBuffer:circularBufferDataPtr length:bytesAvailableCount];
-                //}
-
                 [self convertBuffer:circularBufferDataPtr length:bytesAvailableCount];
 
                 //NSLog(@"AudioMonitor runAudioConverterOnThread - Consume bytesAvailableCount = %d, circularBufferDataPtr = %p", bytesAvailableCount, circularBufferDataPtr);
 
                 TPCircularBufferConsume(&inputCircularBuffer, bytesAvailableCount);
-                
-                ////fwrite(&inputCircularBuffer, 1, bytesAvailableCount, stdout);    // also write to stdout at original sampling rate, for sox, etc.
             }
         }
 
@@ -372,25 +349,6 @@ - (void)runAudioQueueOnThread
         }
     }
 
-    /*
-    bool mIsRunning = true;
-    
-    do {
-            CFRunLoopRunInMode (
-                kCFRunLoopDefaultMode,
-                0.1,
-                false   // returnAfterSourceHandled
-            );
-    } while (mIsRunning == true);
-    
-    // After the audio queue has stopped, runs the run loop a bit longer to ensure that the audio queue buffer currently playing has time to finish
-    CFRunLoopRunInMode (
-        kCFRunLoopDefaultMode,
-        1,
-        false
-    );
-    */
-    
     CFRunLoopRun();
 }
 
@@ -438,8 +396,6 @@ void audioQueueCallback(void *custom_data, AudioQueueRef queue, AudioQueueBuffer
             }
         }
 
-        //fwrite(circularBufferDataPtr, sizeof(SInt16), samplesCount, stdout);    // also write resampled audio to stdout, perhaps for sox, etc.
-
         buffer->mAudioDataByteSize = channelOutputBytes;
 
         if (self.volume > 0.0f)
@@ -467,8 +423,6 @@ void audioQueueCallback(void *custom_data, AudioQueueRef queue, AudioQueueBuffer
 
         memset(buffer->mAudioData, 0, buffer->mAudioDataByteSize);
 
-        //fwrite(buffer->mAudioData, 1, buffer->mAudioDataByteSize, stdout);    // also write silent audio to stdout, perhaps for sox, etc.
-        
         if (self.volume > 0.0f)
         {
             // output silent audio to the current system device
@@ -515,8 +469,8 @@ - (void)convertBuffer:(void *)inputBufferPtr length:(UInt32)dataLength
 
         //NSLog(@"AudioMonitor convertBuffer numFrames=%d, remain=%d", numFrames, audioConverterInputPacketsRemain);
 
-        // for up-sampling (e.g., 10000 Hz to 41000 Hz), AudioConverterFillComplexBuffer was not making multiple calls to inputProc,
-        // so try multiple calls in a loop here and check result for exit condition 'zero' indicating end of input buffer.
+        // for up-sampling (e.g., 10000 Hz to 41000 Hz), use multiple calls to AudioConverterFillComplexBuffer
+        // in a loop here and check result for exit condition 'zero' indicating end of input buffer.
         // Down-sampling (e.g. 85000 Hz to 10000 Hz) seems to get the buffer processed without the loop.
 
         OSStatus convertResult = noErr;
@@ -542,22 +496,29 @@ - (void)convertBuffer:(void *)inputBufferPtr length:(UInt32)dataLength
 
                 void * convertedDataPtr = audioConverterOutputBufferList.mBuffers[0].mData;
 
-                int32_t space;
-                void *ptr = TPCircularBufferHead(&audioConverterCircularBuffer, &space);
-                //NSLog(@"AudioMonitor convertBuffer Produce convertedDataLength = %d, space = %d, head = %p", convertedDataLength, space, ptr);
-                
-                bool  produceBytesResult = TPCircularBufferProduceBytes(&audioConverterCircularBuffer, convertedDataPtr, convertedDataLength);
+                //int32_t space;
+                //void *ptr = TPCircularBufferHead(&audioConverterCircularBuffer, &space);  // for NSLog below
 
                 fwrite(convertedDataPtr, 1, convertedDataLength, stdout);    // also write resampled audio to stdout, perhaps for sox, etc.
+                
+                bool  produceBytesResult = TPCircularBufferProduceBytes(&audioConverterCircularBuffer, convertedDataPtr, convertedDataLength);
 
                 if (produceBytesResult == false)
                 {
-                    // TODO: We are dropping packets here to avoid buffer overrun, is audioConverterCircularBuffer missing consume operations?
+                    // TODO: We are here to avoid buffer overrun, is TPCircularBufferConsume for audioConverterCircularBuffer getting missed somewhere?
 
+                    // clear buffer and try again (not recommended practice)
                     TPCircularBufferClear(&(self->audioConverterCircularBuffer));
+                    
+                    produceBytesResult = TPCircularBufferProduceBytes(&audioConverterCircularBuffer, convertedDataPtr, convertedDataLength);
 
-                    NSLog(@"AudioMonitor convertBuffer Produce convertedDataLength = %d, space = %d, head = %p", convertedDataLength, space, ptr);
-                    NSLog(@"AudioMonitor convertBuffer - produce bytes failed, convertedDataLength = %d", convertedDataLength);
+                    if (produceBytesResult == false)
+                    {
+                        // If we get here, packets will be dropped
+                    
+                        //NSLog(@"AudioMonitor convertBuffer Produce convertedDataLength = %d, space = %d, head = %p", convertedDataLength, space, ptr);
+                        NSLog(@"AudioMonitor convertBuffer - produce bytes failed, convertedDataLength = %d", convertedDataLength);
+                    }
                 }
             }