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/*---- 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
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