Playing PCM data using Audio Queues - ios

Question

I have reffered to this to play a PCM file using Audio Queues.
The code is as follows:
#import "PlayPCM.h"
AudioFileID audioFile;
SInt64 inStartingPacket = 0;
AudioQueueRef audioQueue;
#implementation PlayPCM
void AudioOutputCallback(
void* inUserData,
AudioQueueRef outAQ,
AudioQueueBufferRef outBuffer)
{
AudioStreamPacketDescription* packetDescs;
UInt32 bytesRead;
UInt32 numPackets = 8000;
OSStatus status;
status = AudioFileReadPackets(audioFile,
false,
&bytesRead,
packetDescs,
inStartingPacket,
&numPackets,
outBuffer->mAudioData);
if(numPackets)
{
outBuffer->mAudioDataByteSize = bytesRead;
status = AudioQueueEnqueueBuffer(audioQueue,
outBuffer,
0,
packetDescs);
inStartingPacket += numPackets;
}
else
{
NSLog(#"number of packets = null ") ;
AudioQueueFreeBuffer(audioQueue, outBuffer);
}
}
-(id)init{
if (self = [super init]) {
}
return self;
}
- (void)setupAudioFormat
{
NSLog(#"setting format");
format.mFormatID = kAudioFormatLinearPCM;
format.mSampleRate = 44100;
format.mFramesPerPacket = 1;
format.mChannelsPerFrame = 1;
format.mBytesPerFrame = 2;
format.mBytesPerPacket = 2;
format.mBitsPerChannel = 16;
format.mFormatFlags = kLinearPCMFormatFlagIsBigEndian |
kLinearPCMFormatFlagIsSignedInteger |
kLinearPCMFormatFlagIsPacked;
}
- (void)startPlayback
{
int counter = 0;
[self setupAudioFormat];
OSStatus status;
NSString *documentsDirectory = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
NSString *filePath = [documentsDirectory stringByAppendingPathComponent:# "test1.wav"];
NSLog(#"file path = %#",filePath);
//fUrl = [NSURL URLWithPath:#"file:///Users/Inscripts/Desktop/test1.wav"];
fUrl = [NSURL fileURLWithPath:filePath];
//CFURLRef fileURL = (__bridge CFURLRef)(fUrl);
CFURLRef fileURL = CFURLCreateWithString(NULL, (CFStringRef) filePath, NULL);
status = AudioFileOpenURL(fileURL, kAudioFileReadPermission, 0,&audioFile);
NSLog(#"file opening status = %d",(int)status);
if(status == 0)
{ NSLog(#"file opened");
status = AudioQueueNewOutput(&(format),
AudioOutputCallback,
(__bridge void *)(self),
CFRunLoopGetCurrent(),
kCFRunLoopCommonModes,
0,
&audioQueue);
NSLog(#"audio queue create status = %d",(int)status);
if(status == 0)
{
AudioQueueAllocateBuffer(audioQueue, 1600000, &audioQueueBuffer);
AudioOutputCallback((__bridge void *)(self), audioQueue, audioQueueBuffer);
[self performSelector:#selector(startQueue) withObject:self afterDelay:50];
}
}
if(status != 0)
{
NSLog(#"failed");
// labelStatus.text = #"Play failed";
}
}
-(void)startQueue{
NSLog(#"start queue called");
OSStatus status = AudioQueueStart(audioQueue, NULL);
if(status == 0)
{
NSLog(#"ok");
// labelStatus.text = #"Playing";
}
}
test1.wav file is PCM encoded 16 bits per sample, sampling rate 44100 Hertz, stereo.
I can successfully create audio queue and read the file but all I can hear is crackling noise.
Can someone tell me what's the issue?

Answer 1

Is the sound really big endian data - i doubt with WAVE files.
See your format flags, and change them to use little endian data, so: !kLinearPCMFormatFlagIsBigEndian
Also consider using AudioFileOpenURLor related since that will read the actual wave format and you don't have to rely on your audio stream description.

Answer 2

After preparing more audio queue buffers, no more crackling noise.
please refer to apple's doc
...
/* AudioQueueAllocateBuffer(audioQueue, 1600000, &audioQueueBuffer);
AudioOutputCallback((__bridge void *)(self), audioQueue, audioQueueBuffer);*/
/* add more audio queue buffers, ex:3 */
int kNumberOfBuffers = 3;
AudioQueueBufferRef audioQueueBuffer[kNumberOfBuffers];
for (int i = 0; i<kNumberOfBuffers; i++) {
AudioQueueAllocateBuffer(audioQueue, 1600000, &audioQueueBuffer[i]);
AudioOutputCallback((__bridge void *)(self), audioQueue, audioQueueBuffer[i]);
}
[self performSelector:#selector(startQueue) withObject:self afterDelay:50];
...