/* I don't know what's the License for this file, I sent Michiel Bronswijk a email,
                       but I didn't get any response yet. */

               /* This file is taken from the program mp3studio
                   by Sander Steffann & Michiel Bronswijk ! */

/* *** mpeg_format ***
   *** Filename: mpeg_format.c
   *** History: 19980111 Ver 1.00 | Michiel Bronswijk
   ***          19980112 Ver 1.01 | Michiel Bronswijk
   ***          19980115 Ver 1.02 | Michiel Bronswijk
   ***          19980225 Release version 1.00
   *** Description: MPEG audio bitstream identification
   *** Remarks: Ver 1.00 Rev A : The definitions below are not based
   ***          on the official documents so there could be some hidden
   ***          problems if MPEG decides to change things.
   ***          MPEG 1 and 2 will be detected correctly, the special
   ***          Fraunhofer MPEG "2.5" or MPEG 3 will cause 
   ***          incorrect results
   ***          Ver 1.01 : since I use the ISO source now there
   ***          should be no problems for MPEG 1 and 2
   ***          Ver 1.02 : haven't calculated frame size for layer II
   ***          yet, also haven't considered crc-checking and ancillary
   ***          data, dual_channel could also be a problem
   *** Changes: Ver 1.01 : used ISO source for frame header
   ***          Ver 1.02 : added framesize determination, added tables
 */

#include <string.h>
#include <stdio.h>

#include "mpeg_format.h"

struct mpegFrameHeader
  {
    unsigned char synch;
    unsigned char synch_v_l_e;
    unsigned char bri_sf_p_x;
    unsigned char mo_mx_c_o_em;
  };
/* The exact frame header looks like this:

   |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         SYNCH         |V| L |E|  BRI  | SF|P|X| MO| MX|C|O| EM|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   SYNCH        = synchronisation (all 1's)
   V            = MPEG version (1=MPEG 1, 0=MPEG 2)
   L            = layer (11=I, 10=II, 01=III)
   E            = use error-protection
   BRI          = bitrate index
   SF           = sample frequency
   P            = padding
   X            = extension
   MO           = mode (11=single_channel, 10=dual_channel,
   01=joint_stereo, 00=stereo)
   MX           = mode extension
   C            = copyright
   O            = original
   EM           = emphasis   
 */

/* table with samplesrates */
int samplerates[2][4] =
{				/* MPEG 2 */
  {22050, 24000, 16000, 0},
	  /* MPEG 1 */
  {44100, 48000, 32000, 0}
};

/* table with bitrates */
int bitrates[2][3][15] =
{
  {				/* MPEG 2 */
    {0, 32, 48, 56, 64, 80, 96, 112, 128, 144, 160, 176, 192, 224, 256},
    {0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160},
    {0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160}
  },
  {				/* MPEG 1 */
    {0, 32, 64, 96, 128, 160, 192, 224, 256, 288, 320, 352, 384, 416, 448},
    {0, 32, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, 384},
    {0, 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320}
  }};

/* *** mpegGetFormat ***
   *** History: 19980111 Ver 1.00 | Michiel Bronswijk
   ***          19980112 Ver 1.01 | Michiel Bronswijk
   ***          19980115 Ver 1.02 | Michiel Bronswijk
   *** Description: Returns format information for the MPEG bitstream
   ***              that should be present in buf
   *** Remarks: Fraunhofer MPEG 2.5 causes problems
   ***          Ver 1.02 : calculating frame size is not complete
   *** Changes: Ver 1.01 : using ISO source for frame header
   ***          Ver 1.02 : now using tables and calculating frame size
 */
void
mpegGetFormat (const void *buf, struct mpegformat_t *returnformat)
{
  struct mpegFrameHeader workheader;
/*   int temp, temp2; */
  int h_version, h_layer, h_bitrate, h_samplerate;

  memcpy (&workheader, buf, sizeof (struct mpegFrameHeader));

  /* determine MPEG version */
  h_version = (workheader.synch_v_l_e & 0x08) >> 3;
  returnformat->version = 2 - h_version;
  if ((returnformat->version != 1) &&
      (returnformat->version != 2))
    returnformat->version = -1;

  /* determine layer */
  h_layer = 3 - ((workheader.synch_v_l_e & 0x06) >> 1);
  returnformat->layer = 1 + h_layer;
  if ((returnformat->layer < 1) ||
      (returnformat->layer > 3))
    returnformat->version = -1;

  /* determine channels */
  returnformat->channels = (workheader.mo_mx_c_o_em >> 6) & 0x03;

  /* determine original samplerate */
  h_samplerate = (workheader.bri_sf_p_x & 0x0C) >> 2;
  returnformat->samplerate = samplerates[h_version][h_samplerate];

  /* determine kilobits per second */
  h_bitrate = (workheader.bri_sf_p_x >> 4) & 0x0f;
  returnformat->kilobitrate =
    bitrates[h_version][h_layer][h_bitrate];

  /* determine framesize in bytes */
  /* !!! NOT COMPLETE !!! */
  switch (returnformat->layer)
    {
    case 1:
      returnformat->framesize =
	bitrates[h_version][h_layer][h_bitrate] * 12000;
      returnformat->framesize /=
	samplerates[h_version][h_samplerate];
      returnformat->framesize /=
	(returnformat->version);
      break;
    case 3:
      returnformat->framesize =
	bitrates[h_version][h_layer][h_bitrate] * 144000;
      returnformat->framesize /=
	samplerates[h_version][h_samplerate];
      returnformat->framesize /=
	(returnformat->version);
      break;
    default:
      returnformat->framesize = 0;
    };

  /* finally, check for valid synch (don't force it) */
  if (workheader.synch != 255)
    returnformat->version = -1;
};