Getting raw sample data of m4a file to draw waveform

Question

I'm using AudioToolbox to access m4a audio files with following code:

UInt32 packetsToRead = 1; //Does it makes difference?

void *buffer = malloc(maxPacketSize * packetsToRead);

for (UInt64 packetIndex = 0; packetIndex < packetCount; packetIndex++)
{
   ioNumberOfPackets = packetsToRead;
   ioNumberOfBytes = maxPacketSize * ioNumberOfPackets;

   AudioFileReadPacketData(audioFile, NO, &ioNumbersOfBytes, NULL, packetIndex, &ioNumberOFPackets, buffer);
    for (UInt32 batchPacketIndex = 0; batchPacketIndex < ioNumberOfPackets; batchPacketIndex++)
    {
    //What to do here to get amplitude value? How to get sample value?
    }
    packetIndex+=ioNumberOfPackets;
}

My audio format is: AppleM4A, 8000 Hz, 16 Bit, 4096 frames per packet

score 1 · Accepted Answer · edited May 23 '17 at 12:19

1

The solution was to use extended audio file services. You just have to set up transition between client format and PCM. Got the right way overthere Audio Processing: Playing with volume level.

edited May 23 '17 at 12:19

Community

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1

answered Sep 12 '11 at 01:50

Denis Mikhaylov

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hotpaw2 · Answer 2 · 2011-09-14T00:14:53.873

0

To get waveform data, you may first need to convert your compressed audio file into raw PCM samples, such as found inside a WAV file, or other non-compressed audio format. Try AVAssetReader, et.al.

edited Sep 14 '11 at 00:14

answered Sep 11 '11 at 05:32

hotpaw2

70,107
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AVAssetReader is way too slow for tge real time analisys. It was my first solution of this problem. – Denis Mikhaylov Sep 12 '11 at 01:51

Getting raw sample data of m4a file to draw waveform

2 Answers2