EXC_BAD_ACCESS with AudioFileReadPackets - ios

Question

I've been trying to serialize a local audio file following the instructions here, only instead of feeding the packets directly to the AudioQueBuffer, I would like send it over bluetooth/wifi using GKSession. I'm getting an EXC_BAD_ACCESS error:
- (void)broadcastServerMusicWithSession:(GKSession *)session playerName:(NSString *)name clients: (NSArray *)clients
{
self.isServer = YES;
_session = session;
_session.available = NO;
_session.delegate = self;
[_session setDataReceiveHandler:self withContext:nil];
CFURLRef fileURL = (__bridge CFURLRef)[[NSBundle mainBundle] URLForResource:#"mozart" withExtension:#"mp3"]; // file URL
AudioFile *audioFile = [[AudioFile alloc] initWithURL:fileURL];
//no we start sending the data over
#define MAX_PACKET_COUNT 4096
SInt64 currentPacketNumber = 0;
UInt32 numBytes;
UInt32 numPacketsToRead;
AudioStreamPacketDescription packetDescriptions[MAX_PACKET_COUNT];
NSInteger bufferByteSize = 4096;
if (bufferByteSize < audioFile.maxPacketSize) bufferByteSize = audioFile.maxPacketSize;
numPacketsToRead = bufferByteSize/audioFile.maxPacketSize;
UInt32 numPackets = numPacketsToRead;
BOOL isVBR = ([audioFile audioFormatRef]->mBytesPerPacket == 0) ? YES : NO;
// this should be in a do while (numPackets < numPacketsToRead) loop..
// but i took it out just to narrow down the problem
NSMutableData *myBuffer = [[NSMutableData alloc] initWithCapacity:numPackets * audioFile.maxPacketSize];
AudioFileReadPackets (
audioFile.fileID,
NO,
&numBytes,
isVBR ? packetDescriptions : 0,
currentPacketNumber,
&numPackets,
&myBuffer
);
NSError *error;
if (![session sendDataToAllPeers:packetData withDataMode:GKSendDataReliable error:&error])
{
NSLog(#"Error sending data to clients: %#", error);
}
I know for a fact that it's the AudioFileReadPackets call that's breaking the code, since it runs fine if I comment that bit out
I've tried doing Zombies profiling using xcode 4.3, but it just crashes.. one useful debugging tip I got though was breaking when the code crashes and outputting the error code using gdb console.. this is what I get:
(lldb) po [$eax className] NSException
error: warning: receiver type 'unsigned int' is not 'id' or interface pointer, consider casting it to 'id'
warning: declaration does not declare anything
error: expected ';' after expression
error: 1 errors parsing expression
but I couldn't do much with it.. any help?

Answer 1

Turns out there are two problems with the above code:
[audioFile audioFormatRef]->mBytesPerPacket == 0
the compiler isn't happy with this one.. if you refer to the code that defines audioFormatRef, it returns a pointer to a format struct, which has a mBytesPerPacket field.. I donno why the above syntax isn't working though
I shouldn't be supplying myBuffer to the AudioFileReadPackets function (type mistmach).. rather I should do something like this:
NSMutableData *myBuffer = [[NSMutableData alloc] initWithCapacity:numPackets * audioFile.maxPacketSize];
const void *buffer = [myBuffer bytes];
AudioFileReadPackets (
audioFile.fileID,
NO,
&numBytes,
isVBR ? packetDescriptions : 0,
currentPacketNumber,
&numPackets,
buffer
);
this works too
void *buffer = [myBuffer mutablebytes];
read this post to explain the difference between those two options