CODEWITHSUNDEEP
c#iosaudioxamarinstreaming
user6196834
user6196834

Reputation: 33

Recording live Audio Streams on iOS

//Declare string for application temp path and tack on the file extension
string fileName = string.Format ("Myfile{0}.wav", DateTime.Now.ToString ("yyyyMMddHHmmss"));
string audioFilePath = Path.Combine (Path.GetTempPath (), fileName);

Console.WriteLine("Audio File Path: " + audioFilePath);

url = NSUrl.FromFilename(audioFilePath);
//set up the NSObject Array of values that will be combined with the keys to make the NSDictionary
NSObject[] values = new NSObject[]
{
    NSNumber.FromFloat (44100.0f), //Sample Rate
    NSNumber.FromInt32 ((int)AudioToolbox.AudioFormatType.LinearPCM), //AVFormat
    NSNumber.FromInt32 (2), //Channels
    NSNumber.FromInt32 (16), //PCMBitDepth
    NSNumber.FromBoolean (false), //IsBigEndianKey
    NSNumber.FromBoolean (false) //IsFloatKey
};

//Set up the NSObject Array of keys that will be combined with the values to make the NSDictionary
NSObject[] keys = new NSObject[]
{
    AVAudioSettings.AVSampleRateKey,
    AVAudioSettings.AVFormatIDKey,
    AVAudioSettings.AVNumberOfChannelsKey,
    AVAudioSettings.AVLinearPCMBitDepthKey,
    AVAudioSettings.AVLinearPCMIsBigEndianKey,
    AVAudioSettings.AVLinearPCMIsFloatKey
};

//Set Settings with the Values and Keys to create the NSDictionary
settings = NSDictionary.FromObjectsAndKeys (values, keys);

//Set recorder parameters
recorder = AVAudioRecorder.Create(url, new AudioSettings(settings), out error);

//Set Recorder to Prepare To Record
recorder.PrepareToRecord();

This code works well, but how can you keep a record from a microphone directly to stream? I did not find any information in the Internet, i hope you can help me

Upvotes: 3

Views: 1552

Answers (1)

SushiHangover
SushiHangover

Reputation: 74209

You are looking for buffered access to the audio stream (recording or playback), iOS provides it via Audio Queue Services (AVAudioRecorder is too high level), so then as audio buffers are filled, iOS calls your callback with a filled buffer from the queue, you do something with it (save it to disk, write it to a C#-based Stream, send to a playback audio queue [speakers], etc...) and, normally, place it back into the queue for reuse.

Something like this starts recording to queue of audio buffers:

var recordFormat = new AudioStreamBasicDescription() {
    SampleRate = 8000,
    Format = AudioFormatType.LinearPCM,
    FormatFlags = AudioFormatFlags.LinearPCMIsSignedInteger | AudioFormatFlags.LinearPCMIsPacked,
    FramesPerPacket = 1,
    ChannelsPerFrame = 1,
    BitsPerChannel = 16,
    BytesPerPacket = 2,
    BytesPerFrame = 2,
    Reserved = 0
};

recorder = new InputAudioQueue (recordFormat);

for (int count = 0; count < BufferCount; count++) {
    IntPtr bufferPointer;
    recorder.AllocateBuffer(AudioBufferSize, out bufferPointer);
    recorder.EnqueueBuffer(bufferPointer, AudioBufferSize, null);
}
recorder.InputCompleted += HandleInputCompleted;
recorder.Start ();

So assuming a AudioBufferSize of 8k and a BufferCount of 3 in this example, so once the first of three buffers is filled, our handler HandleInputCompleted is called (since there are 2 buffers still in the queue recording continues to them.

Our InputCompleted handler:

private void HandleInputCompleted (object sender, InputCompletedEventArgs e)
{
    // We received a new buffer of audio, do something with it....

    // Some unsafe code will be required to rip the buffer...

    // Place the buffer back into the queue so iOS knows you are done with it
    recorder.EnqueueBuffer(e.IntPtrBuffer, AudioBufferSize, null);

    // At some point you need to call `recorder.Stop();`  ;-)
}

(I ripped out our code from the handler as it is a custom audio-2-text learning neutral network as we use really small buffers in a very large queue to reduce feedback latency and load that audio data within single TCP/UDP packets for cloud processing (think Siri ;-)

In this handler you have access to the Pointer to the buffer that is currently filled via InputCompletedEventArgs.IntPtrBuffer, Using that pointer you could peek each byte in the buffer and poke them to your C#-based Stream if that is your goal.

Apple has a great tech article concerning Audio Queue: https://developer.apple.com/library/ios/documentation/MusicAudio/Conceptual/AudioQueueProgrammingGuide/AboutAudioQueues/AboutAudioQueues.html

Upvotes: 4

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