The processing pipeline is slightly revised in this commit. The AudioMonitor object uses the same stdin data from rtl_fm_localradio, but the pass-through data is now always resampled to 48000 Hz before it is written to stdout. Before this change, the next stage in the pipeline, a Sox process, was used to resample the data. Sox no longer does the resampling since AudioMonitor has already performed that task. However, the Sox process remains in place to apply other filters, like deemphasis.

A few audio packets are still getting dropped periodically, like in a batch of several dozen SInt16 samples every second, but the audio seems to sound okay anyway.

More good news: moving the 48000 Hz resampling process to an earlier stage seems to fix the MP3 player stream stall problem with the <audio> element with Safari and Cocoa WebView on Mac and iOS.  Most features seem to be running smoother now.

The version was incremented to 1.12-alpha.

Author: dsward2

AudioMonitor/AudioMonitor/AudioMonitor.mm

@@ -85,6 +85,7 @@ - (void)runInputBufferOnThread
     NSTimeInterval lastReadTime = [NSDate timeIntervalSinceReferenceDate] + 20;
     NSTimeInterval nextTimeoutReportInterval = 5;
 
+    //int32_t circularBufferLength = 512 * 1024;
     int32_t circularBufferLength = 256 * 1024;
     TPCircularBufferInit(&inputCircularBuffer, circularBufferLength);
 
@@ -148,11 +149,13 @@ - (void)runInputBufferOnThread
 
                         if (produceBytesResult == false)
                         {
+                            TPCircularBufferClear(&inputCircularBuffer);
+
                             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.
+                        //fwrite(rtlsdrBuffer, 1, bytesAvailableCount, stdout); // also write to stdout at original sampling rate, for sox, etc.
                     }
 
                     free(rtlsdrBuffer);
@@ -200,7 +203,8 @@ - (void)runAudioConverterOnThread
     NSTimeInterval lastReadTime = [NSDate timeIntervalSinceReferenceDate] + 20;
     NSTimeInterval nextTimeoutReportInterval = 5;
 
-    int32_t circularBufferLength = 384 * 1024;
+    //int32_t circularBufferLength = 256 * 1024;
+    int32_t circularBufferLength = 128 * 1024;
     TPCircularBufferInit(&audioConverterCircularBuffer, circularBufferLength);
 
     [self startAudioConverter];     // resample PCM data to 48000 Hz
@@ -224,6 +228,9 @@ - (void)runAudioConverterOnThread
         if( bytesAvailableCount <= 0)
         {
             //[NSThread sleepForTimeInterval:0.01f];
+
+            //TPCircularBufferClear(&inputCircularBuffer);
+
             usleep(1000);
         }
         else
@@ -235,16 +242,18 @@ - (void)runAudioConverterOnThread
 
                 //NSLog(@"AudioMonitor sending data, length=%ld", bytesAvailableCount);
 
-                if (self.volume > 0.0f)
-                {
-                    [self convertBuffer:circularBufferDataPtr length: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.
+                ////fwrite(&inputCircularBuffer, 1, bytesAvailableCount, stdout);    // also write to stdout at original sampling rate, for sox, etc.
             }
         }
 
@@ -305,6 +314,8 @@ - (void)runAudioQueueOnThread
 {
     [NSThread sleepForTimeInterval:0.2f];
 
+    if (self.volume > 0.0f)
+    {
     // configure AudioQueue for rendering PCM audio data to default output device (i.e., speakers).
 
     audioQueueIndex = 0;
@@ -313,7 +324,7 @@ - (void)runAudioQueueOnThread
 
     audioQueueDescription.mSampleRate       = kAudioQueueSampleRate;
     audioQueueDescription.mFormatID         = kAudioFormatLinearPCM;
-    audioQueueDescription.mFormatFlags      = kLinearPCMFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked;
+    audioQueueDescription.mFormatFlags      = kLinearPCMFormatFlagIsSignedInteger | kLinearPCMFormatFlagIsPacked | kAudioFormatFlagIsNonInterleaved;
     audioQueueDescription.mBitsPerChannel   = 8 * sizeof(SInt16);
     audioQueueDescription.mChannelsPerFrame = kAudioQueueChannelsCount;
     audioQueueDescription.mBytesPerFrame    = sizeof(SInt16) * kAudioQueueChannelsCount;
@@ -345,18 +356,20 @@ - (void)runAudioQueueOnThread
 
     UInt32 inNumberOfFramesToPrepare = 0;   // decode all enqueued buffers
     UInt32 outNumberOfFramesPrepared = 0;
-    OSStatus queuePrimeStatus = AudioQueuePrime(audioQueue, inNumberOfFramesToPrepare, &outNumberOfFramesPrepared);
-    if (queuePrimeStatus != noErr)
-    {
-        NSError * error = [NSError errorWithDomain:NSOSStatusErrorDomain code:queuePrimeStatus userInfo:NULL];
-        NSLog(@"AudioMonitor runAudioQueueOnThread queuePrimeStatus %@", error);
-    }
-	
-    OSStatus queueStartStatus = AudioQueueStart(audioQueue, NULL);
-    if (queueStartStatus != noErr)
-    {
-        NSError * error = [NSError errorWithDomain:NSOSStatusErrorDomain code:queueStartStatus userInfo:NULL];
-        NSLog(@"AudioMonitor runAudioQueueOnThread queueStartStatus %@", error);
+    
+        OSStatus queuePrimeStatus = AudioQueuePrime(audioQueue, inNumberOfFramesToPrepare, &outNumberOfFramesPrepared);
+        if (queuePrimeStatus != noErr)
+        {
+            NSError * error = [NSError errorWithDomain:NSOSStatusErrorDomain code:queuePrimeStatus userInfo:NULL];
+            NSLog(@"AudioMonitor runAudioQueueOnThread queuePrimeStatus %@", error);
+        }
+        
+        OSStatus queueStartStatus = AudioQueueStart(audioQueue, NULL);
+        if (queueStartStatus != noErr)
+        {
+            NSError * error = [NSError errorWithDomain:NSOSStatusErrorDomain code:queueStartStatus userInfo:NULL];
+            NSLog(@"AudioMonitor runAudioQueueOnThread queueStartStatus %@", error);
+        }
     }
 
     /*
@@ -393,6 +406,7 @@ void audioQueueCallback(void *custom_data, AudioQueueRef queue, AudioQueueBuffer
 
     AudioMonitor * self = (__bridge AudioMonitor *)custom_data;
 
+    // get pointer to resampled LPCM data for reading
     int32_t availableBytes = 0;
     void * circularBufferDataPtr = TPCircularBufferTail(&(self->audioConverterCircularBuffer), &availableBytes);
 
@@ -424,21 +438,24 @@ void audioQueueCallback(void *custom_data, AudioQueueRef queue, AudioQueueBuffer
             }
         }
 
-        //NSLog(@"AudioMonitor audioQueueCallback - Consume availableBytes = %d, circularBufferDataPtr = %p", availableBytes, circularBufferDataPtr);
-        
-        TPCircularBufferConsume(&(self->audioConverterCircularBuffer), availableBytes);
-
-        //fwrite(circularBufferDataPtr, 1, availableBytes, stdout);    // also write resampled audio to stdout, perhaps for sox, etc.
+        //fwrite(circularBufferDataPtr, sizeof(SInt16), samplesCount, stdout);    // also write resampled audio to stdout, perhaps for sox, etc.
 
         buffer->mAudioDataByteSize = channelOutputBytes;
 
-        // output resampled audio to the current system device
-        OSStatus queueEnqueueStatus = AudioQueueEnqueueBuffer(queue, buffer, 0, NULL);
-        if (queueEnqueueStatus != noErr)
+        if (self.volume > 0.0f)
         {
-            NSError * error = [NSError errorWithDomain:NSOSStatusErrorDomain code:queueEnqueueStatus userInfo:NULL];
-            NSLog(@"AudioMonitor runAudioQueueOnThread data queueEnqueueStatus %@", error);
+            // output resampled audio to the current system device
+            OSStatus queueEnqueueStatus = AudioQueueEnqueueBuffer(queue, buffer, 0, NULL);
+            if (queueEnqueueStatus != noErr)
+            {
+                NSError * error = [NSError errorWithDomain:NSOSStatusErrorDomain code:queueEnqueueStatus userInfo:NULL];
+                NSLog(@"AudioMonitor runAudioQueueOnThread data queueEnqueueStatus %@", error);
+            }
         }
+
+        //NSLog(@"AudioMonitor audioQueueCallback - Consume availableBytes = %d, circularBufferDataPtr = %p", availableBytes, circularBufferDataPtr);
+
+        TPCircularBufferConsume(&(self->audioConverterCircularBuffer), availableBytes);
     }
     else
     {
@@ -449,13 +466,18 @@ void audioQueueCallback(void *custom_data, AudioQueueRef queue, AudioQueueBuffer
         buffer->mAudioDataByteSize = sizeof(SInt16) * 256;      // 64 frames * 2 bytes per packet * 2 packets per frame
 
         memset(buffer->mAudioData, 0, buffer->mAudioDataByteSize);
+
+        //fwrite(buffer->mAudioData, 1, buffer->mAudioDataByteSize, stdout);    // also write silent audio to stdout, perhaps for sox, etc.
 
-        // output silent audio to the current system device
-        OSStatus queueEnqueueStatus = AudioQueueEnqueueBuffer(queue, buffer, 0, NULL);
-        if (queueEnqueueStatus != noErr)
+        if (self.volume > 0.0f)
         {
-            NSError * error = [NSError errorWithDomain:NSOSStatusErrorDomain code:queueEnqueueStatus userInfo:NULL];
-            NSLog(@"AudioMonitor runAudioQueueOnThread silence queueEnqueueStatus %@", error);
+            // output silent audio to the current system device
+            OSStatus queueEnqueueStatus = AudioQueueEnqueueBuffer(queue, buffer, 0, NULL);
+            if (queueEnqueueStatus != noErr)
+            {
+                NSError * error = [NSError errorWithDomain:NSOSStatusErrorDomain code:queueEnqueueStatus userInfo:NULL];
+                NSLog(@"AudioMonitor runAudioQueueOnThread silence queueEnqueueStatus %@", error);
+            }
         }
     }
 }
@@ -514,6 +536,8 @@ - (void)convertBuffer:(void *)inputBufferPtr length:(UInt32)dataLength
 
             if (outputDataPacketSize > 0)   // number of packets converted
             {
+                // produce resampled audio to second circular buffer
+                
                 int32_t convertedDataLength = outputDataPacketSize * sizeof(SInt16);
 
                 void * convertedDataPtr = audioConverterOutputBufferList.mBuffers[0].mData;
@@ -524,8 +548,14 @@ - (void)convertBuffer:(void *)inputBufferPtr length:(UInt32)dataLength
 
                 bool  produceBytesResult = TPCircularBufferProduceBytes(&audioConverterCircularBuffer, convertedDataPtr, convertedDataLength);
 
+                fwrite(convertedDataPtr, 1, convertedDataLength, stdout);    // also write resampled audio to stdout, perhaps for sox, etc.
+
                 if (produceBytesResult == false)
                 {
+                    // TODO: We are dropping packets here to avoid buffer overrun, is audioConverterCircularBuffer missing consume operations?
+                
+                    TPCircularBufferClear(&(self->audioConverterCircularBuffer));
+
                     NSLog(@"AudioMonitor convertBuffer Produce convertedDataLength = %d, space = %d, head = %p", convertedDataLength, space, ptr);
                     NSLog(@"AudioMonitor convertBuffer - produce bytes failed, convertedDataLength = %d", convertedDataLength);
                 }
@@ -662,7 +692,7 @@ - (void)logDescription:(AudioStreamBasicDescription *)asbd withName:(NSString *)
     NSLog(@"AudioStreamBasicDescription %@", name);
     NSLog(@"   %@.mSampleRate=%f", name, asbd->mSampleRate);
     NSLog(@"   %@.mFormatID=%c4", name, asbd->mFormatID);
-    NSLog(@"   %@.AudioFormatFlags=%u", name, (unsigned int)asbd->mFormatFlags);
+    NSLog(@"   %@.mFormatFlags=%u", name, (unsigned int)asbd->mFormatFlags);
     NSLog(@"   %@.mBytesPerPacket=%u", name, (unsigned int)asbd->mBytesPerPacket);
     NSLog(@"   %@.mFramesPerPacket=%u", name, (unsigned int)asbd->mFramesPerPacket);
     NSLog(@"   %@.mBytesPerFrame=%u", name, (unsigned int)asbd->mBytesPerFrame);

LocalRadio/Info.plist

@@ -17,9 +17,9 @@
 	<key>CFBundlePackageType</key>
 	<string>APPL</string>
 	<key>CFBundleShortVersionString</key>
-	<string>1.11</string>
+	<string>1.12</string>
 	<key>CFBundleVersion</key>
-	<string>12</string>
+	<string>13</string>
 	<key>LSApplicationCategoryType</key>
 	<string>public.app-category.entertainment</string>
 	<key>LSMinimumSystemVersion</key>

LocalRadio/SDRController.m

@@ -545,7 +545,8 @@ - (void)dispatchedStartRtlsdrTasksForFrequencies:(NSArray *)frequenciesArray cat
         // configure rtl_fm_localradio for output to UDPSender (then to EZStream/Icecast)
 
         [soxArgsArray addObject:@"-r"];
-        [soxArgsArray addObject:tunerSampleRateNumber];
+        //[soxArgsArray addObject:tunerSampleRateNumber];
+        [soxArgsArray addObject:@"48000"];      // assume input from AudioMonitor already resampled to 48000 Hz
 
         [soxArgsArray addObject:@"-e"];
         [soxArgsArray addObject:@"signed-integer"];
@@ -606,7 +607,8 @@ - (void)dispatchedStartRtlsdrTasksForFrequencies:(NSArray *)frequenciesArray cat
         // input args
 
         [soxArgsArray addObject:@"-r"];
-        [soxArgsArray addObject:tunerSampleRateNumber];
+        //[soxArgsArray addObject:tunerSampleRateNumber];
+        [soxArgsArray addObject:@"48000"];      // assume input from AudioMonitor already resampled to 48000 Hz
 
         [soxArgsArray addObject:@"-e"];
         [soxArgsArray addObject:@"signed-integer"];

README.md

@@ -7,7 +7,7 @@
 
 <hr>
 
-### The latest pre-release alpha versions of the LocalRadio app are [avaiable for download at this link](https://github.com/dsward2/LocalRadio/releases).
+### The latest pre-release alpha versions of the LocalRadio app are [available for download at this link](https://github.com/dsward2/LocalRadio/releases).
 
 <hr>