Record audio to NSData

Question

I have set up a TCP connection between two iPhones and I am able to send NSData packages between the two. I would like to talk into the microphone and get the recording as an NSData object and send this to the other iPhone. I have successfulyl used Audio Queue Services to record audio and play it but I have not managed to get the recording as NSData. I posted a question about converting the recording to NSData when using Audio Queue Services but it has not got me any further.

Therefore I would like to hear if there is any other approach I can take to speak into the microphone of an iPhone and have the input as raw data?

Update:

I need to send the packages continuous while recording. E.g. every second while recording I will send the data recorded during that second.

Strutting

Answer 1

Both Audio Queues and the RemoteIO Audio Unit will give you buffers of raw audio in real-time with fairly low latency. You can take the buffer pointer and the byte length given in each audio callback to create a new block of NSData. RemoteIO will provide the lowest latency, but may require the network messaging to be done outside the callback thread.

Microcline

If I understand you correctly I should be able to use my current Audio Queues and in my AudioInputCallback do the following? NSUInteger length = inNumberPacketDescriptions * 2; NSData *packet = [NSData dataWithBytes:inBuffer->mAudioData length:length];. Is that right? I multiply by two because this should be the amount of bytes in each of my packets (this is set in the AudioStreamBasicDescription) According to idevhub.com/exploring-iphone-audio-part-1 EDIT: It seems that I cannot call self in my callback, though. – Strutting

Call self outside the audio callback. Set a flag inside the callback, and poll it from the outside that self needs to be called with some data. – Microcline

It seems to work now. You don't happen to have an idea how I would play the received data when the data comes continous? – Strutting

The data doesn't really come over the network continuously. You need a strategy to deal with network latency jitter and non-synchronous audio sample rates. Those are two large separate questions. – Microcline

I guess sending the NSData packets and adding those to a queue for playing is not an option then. – Strutting

It is an option, but expect some possible problems, depending on the queue size and other factors. – Microcline

Answer 2

Using AVAudioRecorder like this:

NSURL *filePath = //Your desired path for the file
NSDictionary *settings; //The settings for the recorded file
NSError *error = nil;
AVAudioRecorder *recorder = [[AVAudioRecorder alloc] initWithURL:filePath settings:recordSetting error:&error];
....
[recorder record];
....
[recorder stop];
....

And the retrieve the NSData from the file:

NSData *audioData = [[NSData alloc] initWithContentsOfFile:filePath];

AVAudioRecorder reference, here.

Edit:

In order to retrieve chunks of the recorded audio you could use the subdataWithRange: method in the NSData class. Keep an offset from which you wish to retrieve the bytes. You can have a NSTimer getting fired every second so you can collect the bytes and send them. You will need to find out how many bytes are getting recorded every second.

Gildea

I need to send the packages continuous while recording. E.g. every second while recording I will send the data recorded during that second. Will that be possible with the solution you mention? I'm sorry that I didn't clarify that in my question. – Strutting

Answer 3

This is what I did on the recording iphone:

void AudioInputCallback(void * inUserData,
                    AudioQueueRef inAQ,
                    AudioQueueBufferRef inBuffer,
                    const AudioTimeStamp * inStartTime,
                    UInt32 inNumberPacketDescriptions,
                    const AudioStreamPacketDescription * inPacketDescs)
{
RecordState * recordState = (RecordState*)inUserData;
if (!recordState->recording)
{
    printf("Not recording, returning\n");
}

// if (inNumberPacketDescriptions == 0 && recordState->dataFormat.mBytesPerPacket != 0)
// {
//     inNumberPacketDescriptions = inBuffer->mAudioDataByteSize / recordState->dataFormat.mBytesPerPacket;
// }

printf("Writing buffer %lld\n", recordState->currentPacket);

OSStatus status = AudioFileWritePackets(recordState->audioFile,
                                        false,
                                        inBuffer->mAudioDataByteSize,
                                        inPacketDescs,
                                        recordState->currentPacket,
                                        &inNumberPacketDescriptions,
                                        inBuffer->mAudioData);
NSLog(@"DATA = %@",[NSData dataWithBytes:inBuffer->mAudioData length:inBuffer->mAudioDataByteSize]);

[[NSNotificationCenter defaultCenter] postNotificationName:@"Recording" object:[NSData dataWithBytes:inBuffer->mAudioData length:inBuffer->mAudioDataByteSize]];

if (status == 0)
{
    recordState->currentPacket += inNumberPacketDescriptions;
}

AudioQueueEnqueueBuffer(recordState->queue, inBuffer, 0, NULL);
}

I have called upon a notification which help to send data packets to the other iPhone in the network.

But I do not know how to read the data on the other side. I am still trying to figure out how that works. I will surely update once I do that.

Neelon

Don't ask question in an answer. Please, edit question, add comment to make problem more clear, but not put an question in an answer – Hilltop