// Generate ADTS header (Fluendo)
//
// http://wiki.multimedia.cx/index.php?title=ADTS
// http://wiki.multimedia.cx/?title=Understanding_AAC
// http://wiki.multimedia.cx/index.php?title=MPEG-4_Audio
void GenerateADTS(int data_length)
{
  int obj_type = 2 - 1;  // AAC LC

  int length = data_length + 7;
  int rate_idx = 0;

  if (samplerate == 22050)
          rate_idx = 7;
  else if (samplerate == 44100)
          rate_idx = 4;
  else {
          fprintf(stderr, "[-] Unhandled sample rate %ld!\n", samplerate);
          exit(-1);
  }

  memset(adts_header, 0, 7);

  /* Sync point over a full byte */
  adts_header[0] = 0xFF;
  /* Sync point continued over first 4 bits + static 4 bits
   * (ID, layer, protection)*/
  adts_header[1] = 0xF1; // CRC is absent
  /* Object type over first 2 bits */
  adts_header[2] = obj_type << 6;
  /* rate index over next 4 bits */
  adts_header[2] |= (rate_idx << 2);
  /* channels over last 2 bits */
  adts_header[2] |= (channels & 0x4) >> 2;
  /* channels continued over next 2 bits + 4 bits at zero */
  adts_header[3] = (channels & 0x3) << 6;
  /* frame size over last 2 bits */
  adts_header[3] |= (length & 0x1800) >> 11;
  /* frame size continued over full byte */
  adts_header[4] = (length & 0x1FF8) >> 3;
  /* frame size continued first 3 bits */
  adts_header[5] = (length & 0x7) << 5;
  /* buffer fullness (0x7FF for VBR) over 5 last bits*/
  // adts_header[5] |= 0x1F;
  adts_header[5] |= 0x00;  // CBR
  /* buffer fullness (0x7FF for VBR) continued over 6 first bits + 2 zeros for
   * number of raw data blocks */
  // adts_header[6] = 0xFC;
  adts_header[6] = 0x00;  // CBR

}