Question

I m building an iPhone Application that records sound. I make use of Audio Queue Services, and everything works great for the recording.

The thing is, I m using AudioFileWritePackets for file writing, and I m trying to put the same "AAC + ADTS" packets to a network socket.

The resulting file is different since some "headers" or "adts header" might be missing. I am searching for ideas on how to write the ADTS header and/or AAC header? Could the community assist me with this or refer me to a guide that demonstrated how to do this?

I currently have my Buffer Handler method:

void Recorder::MyInputBufferHandler(void inUserData,
    AudioQueueRefinAQ, AudioQueueBufferRefinBuffer,
    const AudioTimeStamp*inStartTime,
    UInt32 inNumPackets, 
    const AudioStreamPacketDescription*inPacketDesc) {
        AQRecorder *aqr = (AQRecorder *)inUserData;

        try {
            if (inNumPackets > 0) {
                // write packets to file
            XThrowIfError(AudioFileWritePackets(aqr->mRecordFile,
                    FALSE,
                    inBuffer->mAudioDataByteSize,
                    inPacketDesc,
                    aqr->mRecordPacket,
                    &inNumPackets,
                    inBuffer->mAudioData),
                    "AudioFileWritePackets failed");

                    fprintf(stderr, "Writing.");    

                // We write the Net Buffer.
                [aqr->socket_if writeData :(void *)(inBuffer->mAudioData)
                    :inBuffer->mAudioDataByteSize];

                aqr->mRecordPacket += inNumPackets;
            }

            // if we re not stopping, re-enqueue the buffe so that it gets filled again
            if (aqr->IsRunning()) {
            XThrowIfError(AudioQueueEnqueueBuffer(inAQ, inBuffer, 0, NULL),
                    "AudioQueueEnqueueBuffer failed");
            }

        } 

        catch (CAXException e) {
            char buf[256];
            fprintf(stderr, "Error: %s (%s)
", e.mOperation, e.FormatError(buf));
        }
    }

Answer 1

I ve found the solution for this:

I implemented the callback

  XThrowIfError(
                  AudioFileInitializeWithCallbacks(
                                                   this,
                                                   nil,
                                                   BufferFilled_callback,
                                                   nil,
                                                   nil,
                                                   //kAudioFileCAFType,
                                                   kAudioFileAAC_ADTSType,
                                                   &mRecordFormat,
                                                   kAudioFileFlags_EraseFile,
                                                   &mRecordFile),
                  "InitializeWithCallbacks failed");

... And voilá! The real callback you have to implement is BufferFilled_callback. Here is my implementation:

OSStatus AQRecorder::BufferFilled_callback(
                                           void *                               inUserData,
                                           SInt64                               inPosition,
                                           UInt32                               requestCount,
                                           const void *                         buffer,
                                           UInt32 *                             actualCount) {

    AQRecorder *aqr = (AQRecorder *)inUserData;

    // You can write these bytes to anywhere. 
    // You can build a streaming server 

    return 0;
}

If you want to see more about audio queue services, you can get some ideas from Flipzu for iPhone (ex-app for live broadcasting audio // we have to shut it down because we could not raise money).

https://github.com/lucaslain/Flipzu_iPhone

Best,

Lucas.

Answer 2

I ve recently encountered this issue with the iLBC codec, and arrived at the solution as follows:

Record the audio data you want and just write it to a file. Then, take that file and do an octal dump on it. You can use the -c flag to see ascii characters.

Then, create a separate file that you know doesn t contain the header. This is just your data from the buffers on the audio queue. Octal dump that, and compare.

From this, you should have the header and enough info on how to proceed. Hope this helps.

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