How to analyze the BPM of AAC file or any library for converting AAC to MP3

Question

Hello Friends,

I am iphone developer and developing one mac application now. This is my first project ever in mac platform.

I have to analyze the BPM of the songs files. I have done this work for MP3 using FMOD and SoundTouch library.

But i have to analyze for AAC (M4A ) also but this library doesn't support to AAC format.

I tried to search library for AAC(M4A) and i did not get any thing for that. So we if could convert this AAC file to MP3 file by programatically in cocoa then we could analyze the bpm of that file.

I tried to search for converting AAC to Mp3 in cocoa and i got FAAC library but there is no any documentation for integrating with cocoa and its too complex.

Does anyone know about any other library for analyze BPM for AAC in cocoa project.

Many Many Thanks.

Answer 1

How are you currently using SoundTouch? Do you pass audio samples to the SoundTouch library as you read them? Or do you spawn the soundstretch utility and pass the audio as a file or though a pipe?

I'm not familiar with SoundTouch, but it looks like it wants PCM audio as input, so you're probably already converting to PCM. If you wanted to pass samples of audio to SoundTouch as you receive them, you could decode with FAAC using something like this

#include <stdio.h>
#include <inttypes.h>
#include <faac.h>
#include <neaacdec.h>

#define SAMPLE_SIZE 2 //2 bytes, or 16bits per samle.

int AACDecode(uint8_t *aacData, size_t aacBytes, uint32_t sampleRate, unsigned char channels)
{
    NeAACDecHandle decoder = NeAACDecOpen();
    NeAACDecConfigurationPtr config = NeAACDecGetCurrentConfiguration(decoder);
    NeAACDecFrameInfo info;
    uint8_t *decoded = NULL;
    uint8_t *readPtr = aacData;
    int consumed = 0;

    //If the AAC data is wrapped in ADTS, you don't need the next 2 lines
    //If it's not wrapped in ADTS, you need to know sampleRate, and object type
    //Object type is one of LOW, MAIN, SSR, LTP
    config->defObjectType = LOW;
    config->defSampleRate = sampleRate;
    //If SoundTouch wants it in something other than siged 16bit LE PCM, change this
    config->outputFormat = FAAD_FMT_16BIT;
    if (!NeAACDecSetConfiguration(decoder, config))
    {
        printf("unable to set config\n");
        return 0;
    }

    if (NeAACDecInit(decoder, (unsigned char *)aacData, aacBytes, &sampleRate, &channels) < 0)
    {
        printf("unable to init\n");
        return 0;
    }

    do
    {
        decoded = (char *)NeAACDecDecode(decoder, &info, readPtr, aacBytes);
        if (info.samples > 0)
        {
            size_t decodedBytes = (size_t)info.samples * SAMPLE_SIZE;
            //Pass <decodedBytes> of PCM data, pointed to by <decoded> to soundTouch
        }

        consumed += info.bytesconsumed;
        readPtr += info.bytesconsumed;
    } while (info.error == 0 && consumed < aacBytes);

    NeAACDecClose(decoder);
    return 1;
}

You'd need to link against the FAAD library

Or if you're going the command-line route, maybe something like this:

ffmpeg -i <input_file> raw.wav

raw.wav could then be passed to soundstretch