/*---- DXhead.h -------------------------------------------


decoder MPEG Layer III

handle Xing header


Copyright 1998 Xing Technology Corp.
-----------------------------------------------------------*/
// A Xing header may be present in the ancillary
// data field of the first frame of an mp3 bitstream
// The Xing header (optionally) contains
//      frames      total number of audio frames in the bitstream
//      bytes       total number of bytes in the bitstream
//      toc         table of contents

// toc (table of contents^) gives seek points
// for random access
// the ith entry determines the seek point for
// i-percent duration
// seek point in bytes = (toc[i]/256.0) * total_bitstream_bytes
// e.g. half duration seek point = (toc[50]/256.0) * total_bitstream_bytes

#ifndef __DXHEAD_H
#define __DXHEAD_H

#define FRAMES_FLAG     0x0001
#define BYTES_FLAG      0x0002
#define TOC_FLAG        0x0004
#define VBR_SCALE_FLAG  0x0008

#define FRAMES_AND_BYTES (FRAMES_FLAG | BYTES_FLAG)

// structure to receive extracted header
// toc may be NULL

typedef struct XHEADDATA_s {
    int h_id;       // from MPEG header, 0=MPEG2, 1=MPEG1
    int samprate;   // determined from MPEG header
    int flags;      // from Xing header data
    int frames;     // total bit stream frames from Xing header data
    int bytes;      // total bit stream bytes from Xing header data
    int vbr_scale;  // encoded vbr scale from Xing header data
    unsigned char *toc;  // pointer to unsigned char toc_buffer[100]
                         // may be NULL if toc not desired
} XHEADDATA;

int GetXingHeader(XHEADDATA *X,  unsigned char *buf);

// return 0=fail, 1=success
// X   structure to receive header data (output)
// buf bitstream input 


int SeekPoint(unsigned char TOC[100], int file_bytes, float percent);
// return seekpoint in bytes (may be at eof if percent=100.0)
// TOC = table of contents from Xing header
// file_bytes = number of bytes in mp3 file
// percent = play time percentage of total playtime. May be
//           fractional (e.g. 87.245)


#endif


