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67 lines
2.0 KiB
67 lines
2.0 KiB
/*---- DXhead.h -------------------------------------------
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decoder MPEG Layer III
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handle Xing header
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Copyright 1998 Xing Technology Corp.
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-----------------------------------------------------------*/
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// A Xing header may be present in the ancillary
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// data field of the first frame of an mp3 bitstream
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// The Xing header (optionally) contains
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// frames total number of audio frames in the bitstream
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// bytes total number of bytes in the bitstream
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// toc table of contents
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// toc (table of contents^) gives seek points
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// for random access
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// the ith entry determines the seek point for
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// i-percent duration
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// seek point in bytes = (toc[i]/256.0) * total_bitstream_bytes
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// e.g. half duration seek point = (toc[50]/256.0) * total_bitstream_bytes
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#ifndef __DXHEAD_H
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#define __DXHEAD_H
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#define FRAMES_FLAG 0x0001
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#define BYTES_FLAG 0x0002
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#define TOC_FLAG 0x0004
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#define VBR_SCALE_FLAG 0x0008
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#define FRAMES_AND_BYTES (FRAMES_FLAG | BYTES_FLAG)
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// structure to receive extracted header
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// toc may be NULL
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typedef struct XHEADDATA_s {
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int h_id; // from MPEG header, 0=MPEG2, 1=MPEG1
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int samprate; // determined from MPEG header
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int flags; // from Xing header data
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int frames; // total bit stream frames from Xing header data
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int bytes; // total bit stream bytes from Xing header data
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int vbr_scale; // encoded vbr scale from Xing header data
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unsigned char *toc; // pointer to unsigned char toc_buffer[100]
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// may be NULL if toc not desired
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} XHEADDATA;
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int GetXingHeader(XHEADDATA *X, unsigned char *buf);
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// return 0=fail, 1=success
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// X structure to receive header data (output)
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// buf bitstream input
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int SeekPoint(unsigned char TOC[100], int file_bytes, float percent);
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// return seekpoint in bytes (may be at eof if percent=100.0)
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// TOC = table of contents from Xing header
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// file_bytes = number of bytes in mp3 file
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// percent = play time percentage of total playtime. May be
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// fractional (e.g. 87.245)
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#endif
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