Windows Snippet To Use Built-in ACM MP3 Decoder

mp3acm.c

#include <windows.h>
#include <stdio.h>
#include <assert.h>
#include <mmreg.h>
#include <msacm.h>

#define MP3_BLOCK_SIZE 522
#define SOURCE_MP3 "C:\\audiograbber\\At The Club Last Night\\At_The_Club_Last_Night_-_Haven't_You_Heard.mp3"
#define OUTPUT_PCM_FILE "c:\\dump.pcm"

int g_mp3Drivers = 0;

BOOL CALLBACK acmDriverEnumCallback( HACMDRIVERID hadid, DWORD dwInstance, DWORD fdwSupport ){
  if( fdwSupport & ACMDRIVERDETAILS_SUPPORTF_CODEC ) {
    MMRESULT mmr;

    ACMDRIVERDETAILS details;
    details.cbStruct = sizeof(ACMDRIVERDETAILS);
    mmr = acmDriverDetails( hadid, &details, 0 );

    HACMDRIVER driver;
    mmr = acmDriverOpen( &driver, hadid, 0 );

    int i;
    for(i = 0; i < details.cFormatTags; i++ ){
      ACMFORMATTAGDETAILS fmtDetails;
      ZeroMemory( &fmtDetails, sizeof(fmtDetails) );
      fmtDetails.cbStruct = sizeof(ACMFORMATTAGDETAILS);
      fmtDetails.dwFormatTagIndex = i;
      mmr = acmFormatTagDetails( driver, &fmtDetails, ACM_FORMATTAGDETAILSF_INDEX );
      if( fmtDetails.dwFormatTag == WAVE_FORMAT_MPEGLAYER3 ){
	OutputDebugString( L"Found an MP3-capable ACM codec: " );
	OutputDebugString( details.szLongName );
	OutputDebugString( L"\n" );
	g_mp3Drivers++;
      }
    }
    mmr = acmDriverClose( driver, 0 );
  }
  return true;
}

HACMSTREAM g_mp3stream = NULL;



convertMP3(){
  
  MMRESULT mmr;
  
  // try to find an MP3 codec
  acmDriverEnum( acmDriverEnumCallback, 0, 0 );
  if(g_mp3Drivers == 0){
    OutputDebugString( L"No MP3 decoders found!\n" );
    return E_FAIL;
  }
  
  // find the biggest format size
  DWORD maxFormatSize = 0;
  mmr = acmMetrics( NULL, ACM_METRIC_MAX_SIZE_FORMAT, &maxFormatSize );
  
  // define desired output format
  LPWAVEFORMATEX waveFormat = (LPWAVEFORMATEX) LocalAlloc( LPTR, maxFormatSize );
  waveFormat->wFormatTag = WAVE_FORMAT_PCM;
  waveFormat->nChannels = 2; // stereo
  waveFormat->nSamplesPerSec = 44100; // 44.1kHz
  waveFormat->wBitsPerSample = 16; // 16 bits
  waveFormat->nBlockAlign = 4; // 4 bytes of data at a time are useful (1 sample)
  waveFormat->nAvgBytesPerSec = 4 * 44100; // byte-rate
  waveFormat->cbSize = 0; // no more data to follow
  
  
  // define MP3 input format
  LPMPEGLAYER3WAVEFORMAT mp3format = (LPMPEGLAYER3WAVEFORMAT) LocalAlloc( LPTR, maxFormatSize );
  mp3format->wfx.cbSize = MPEGLAYER3_WFX_EXTRA_BYTES;
  mp3format->wfx.wFormatTag = WAVE_FORMAT_MPEGLAYER3;
  mp3format->wfx.nChannels = 2;
  mp3format->wfx.nAvgBytesPerSec = 128 * (1024 / 8);  // not really used but must be one of 64, 96, 112, 128, 160kbps
  mp3format->wfx.wBitsPerSample = 0;                  // MUST BE ZERO
  mp3format->wfx.nBlockAlign = 1;                     // MUST BE ONE
  mp3format->wfx.nSamplesPerSec = 44100;              // 44.1kHz
  mp3format->fdwFlags = MPEGLAYER3_FLAG_PADDING_OFF;
  mp3format->nBlockSize = MP3_BLOCK_SIZE;             // voodoo value #1
  mp3format->nFramesPerBlock = 1;                     // MUST BE ONE
  mp3format->nCodecDelay = 1393;                      // voodoo value #2
  mp3format->wID = MPEGLAYER3_ID_MPEG;
  
  g_mp3stream = NULL;
  mmr = acmStreamOpen( &g_mp3stream,               // open an ACM conversion stream
  		     NULL,                       // querying all ACM drivers
  		     (LPWAVEFORMATEX) mp3format, // converting from MP3
  		     waveFormat,                 // to WAV
  		     NULL,                       // with no filter
  		     0,                          // or async callbacks
  		     0,                          // (and no data for the callback)
  		     0                           // and no flags
  		     );
  
  LocalFree( mp3format );
  LocalFree( waveFormat );
  
  switch( mmr ) {
   case MMSYSERR_NOERROR:
     break; // success!
   case MMSYSERR_INVALPARAM:
     assert( !"Invalid parameters passed to acmStreamOpen" );
     return E_FAIL;
   case ACMERR_NOTPOSSIBLE:
     assert( !"No ACM filter found capable of decoding MP3" );
     return E_FAIL;
   default:
     assert( !"Some error opening ACM decoding stream!" );
     return E_FAIL;
  }
  
  // MP3 stream converter opened correctly
  // now, let's open a file, read in a bunch of MP3 data, and convert it!
  
  // open file
  FILE *fpIn = fopen( SOURCE_MP3, "rb" );
  if( fpIn == NULL ){
    assert( !"can't open MP3 file!" );
    return E_FAIL;
  }
  
  // find out how big the decompressed buffer will be
  unsigned long rawbufsize = 0;
  mmr = acmStreamSize( g_mp3stream, MP3_BLOCK_SIZE, &rawbufsize, ACM_STREAMSIZEF_SOURCE );
  assert( mmr == 0 );
  assert( rawbufsize > 0 );
  
  // allocate our I/O buffers
  LPBYTE mp3buf = (LPBYTE) LocalAlloc( LPTR, MP3_BLOCK_SIZE );
  LPBYTE rawbuf = (LPBYTE) LocalAlloc( LPTR, rawbufsize );
  
  // prepare the decoder
  ACMSTREAMHEADER mp3streamHead;
  ZeroMemory( &mp3streamHead, sizeof(ACMSTREAMHEADER ) );
  mp3streamHead.cbStruct = sizeof(ACMSTREAMHEADER );
  mp3streamHead.pbSrc = mp3buf;
  mp3streamHead.cbSrcLength = MP3_BLOCK_SIZE;
  mp3streamHead.pbDst = rawbuf;
  mp3streamHead.cbDstLength = rawbufsize;
  mmr = acmStreamPrepareHeader( g_mp3stream, &mp3streamHead, 0 );
  assert( mmr == 0 );
  
  // let's dump this data off to disk (for debug checking!)
  FILE *fpOut = fopen( OUTPUT_PCM_FILE, "wb" );
  if( fpOut == NULL ){
    assert( !"can't output output PCM!" );
    return E_FAIL;
  }
  
  while(1) {
    // suck in some MP3 data
    int count = fread( mp3buf, 1, MP3_BLOCK_SIZE, fpIn );
    if( count != MP3_BLOCK_SIZE )
      break;
  
    // convert the data
    mmr = acmStreamConvert( g_mp3stream, &mp3streamHead, ACM_STREAMCONVERTF_BLOCKALIGN );
    assert( mmr == 0 );
  
    // write the decoded PCM to disk
    count = fwrite( rawbuf, 1, mp3streamHead.cbDstLengthUsed, fpOut );
    assert( count == mp3streamHead.cbDstLengthUsed );
  };
  
  // clean up after yourself like a good little boy
  fclose( fpIn );
  fclose( fpOut );
  mmr = acmStreamUnprepareHeader( g_mp3stream, &mp3streamHead, 0 );
  assert( mmr == 0 );
  LocalFree(rawbuf);
  LocalFree(mp3buf);
  mmr = acmStreamClose( g_mp3stream, 0 );
  assert( mmr == 0 );
  
  return S_OK;
}