Play aac audio from RTMP stream ios - ios

Question

I'm trying to play audio I'm receiving from an RTMP stream (I have managed to play the video part). The audio comes in .aac format. I have the NSData coming. Then I'm putting it into a CMAudiSampleBuffer and enqueing it into a AVSampleBufferAudioRenderer. (Basically I'm doing the same thing that I have done for the video packets).
Everything is going fine except that I get no sound. Now I'm pretty new to objective-c and iOS programming so the issue ight come from somewhere else, all ideas are welcome.
Here is the code I use to make the format description
-(void)createFormatDescription:(NSData*)payload
{
OSStatus status;
NSData* data = [NSData dataWithData:[payload subdataWithRange:NSMakeRange(2, [payload length]-2)]];
const uint8_t* bytesBuffer = [data bytes];
_type = bytesBuffer[0]>>3;
_frequency = [self getSampleRate:(bytesBuffer[0] & 0b00000111) << 1 | (bytesBuffer[1] >> 7)];
_channel = (bytesBuffer[1] & 0b01111000) >> 3;
AudioStreamBasicDescription audioFormat;
audioFormat.mFormatID = kAudioFormatMPEG4AAC;
audioFormat.mSampleRate = _frequency;
audioFormat.mFormatFlags = _type;
audioFormat.mBytesPerPacket = 0;
audioFormat.mFramesPerPacket = 1024;
audioFormat.mBytesPerFrame = 0;
audioFormat.mChannelsPerFrame = _channel;
audioFormat.mBitsPerChannel = 0;
audioFormat.mReserved = 0;
status = CMAudioFormatDescriptionCreate(kCFAllocatorDefault, &audioFormat, 0, nil, 0, nil, nil, &_formatDesc);
}
Here is the code that I use the add the adts data in front of the packets and create the buffers :
- (NSData*) adts:(int)length
{
int size = 7;
int fullSize =length + size;
uint8_t adts[size];
adts[0] = 0xFF;
adts[1] = 0xF9;
adts[2] = (_type - 1) << 6 | (_frequency << 2) | (_channel >> 2);
adts[3] = (_channel & 3) << 6 | (fullSize >> 11);
adts[4] = (fullSize & 0x7FF) >> 3;
adts[5] = ((fullSize & 7) << 5) + 0x1F;
adts[6] = 0xFC;
NSData* result = [NSData dataWithBytes:adts length:size];
return result;
}
-(void)enqueueBuffer:(RTMPMessage*)message {
OSStatus status;
NSData* payloadData = [NSData dataWithData:[message.payloadData
subdataWithRange:NSMakeRange(2, [message.payloadData length]-2)]];
NSData* adts = [NSData dataWithData:[self adts:(int)[payloadData length]]];
NSMutableData* data = [NSMutableData dataWithData:adts];
[data appendData:payloadData];
uint8_t* bytesBuffer[[data length]];
[data getBytes:bytesBuffer length:[data length]];
const size_t sampleSize = [data length];
AudioStreamPacketDescription packetDescription;
packetDescription.mDataByteSize = (int)sampleSize;
packetDescription.mStartOffset = 0;
packetDescription.mVariableFramesInPacket = 0;
CMBlockBufferRef blockBuffer = NULL;
CMSampleBufferRef sampleBuffer = NULL;
CMTime time = CMTimeMake(5, _frequency);
status = CMBlockBufferCreateWithMemoryBlock(NULL, bytesBuffer, [data length], kCFAllocatorNull, NULL, 0, [data length], 0, &blockBuffer);
status = CMAudioSampleBufferCreateWithPacketDescriptions(kCFAllocatorDefault, blockBuffer, true, NULL, NULL, _formatDesc, 1, time, &packetDescription, &sampleBuffer);
CFArrayRef attachments = CMSampleBufferGetSampleAttachmentsArray(sampleBuffer, YES);
CFMutableDictionaryRef dict = (CFMutableDictionaryRef)CFArrayGetValueAtIndex(attachments, 0);
CFDictionarySetValue(dict, kCMSampleAttachmentKey_DisplayImmediately, kCFBooleanTrue);
[_audioRenderer enqueueSampleBuffer:sampleBuffer];
}
Thanks in advance for any help

Answer 1

ADTS header is not required. AVAudioSampleRenderer just need naked aac compressed packet for playing. But the precondition is that you set the correct formatDescription, and correct parameters for samplebuffer creation.
You need aware that, HE-AAC(LC+SBR) packed like a AAC-LC, but has 22050 sample rate. HE-V2(LC+SBR+PS) packed like a AAC-LC, but has 22050 sample rate, and one channel per sample.
And all HE-AAC(v1,v2), samplesPerFrame always 2048, not like LC's 1024.
That's all I know how to play aac stream with AVAudioSampleRenderer correctly. It's a long way succeed..