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130 lines
2.7 KiB
130 lines
2.7 KiB
15 years ago
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/*---- DXhead.c --------------------------------------------
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decoder MPEG Layer III
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handle Xing header
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mod 12/7/98 add vbr scale
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Copyright 1998 Xing Technology Corp.
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-----------------------------------------------------------*/
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#include <stdlib.h>
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#include <stdio.h>
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#include <float.h>
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#include <math.h>
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#include "dxHead.h"
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// 4 Xing
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// 4 flags
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// 4 frames
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// 4 bytes
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// 100 toc
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/*-------------------------------------------------------------*/
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static int ExtractI4(unsigned char *buf)
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{
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int x;
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// big endian extract
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x = buf[0];
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x <<= 8;
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x |= buf[1];
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x <<= 8;
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x |= buf[2];
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x <<= 8;
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x |= buf[3];
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return x;
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}
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/*-------------------------------------------------------------*/
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int GetXingHeader(XHEADDATA *X, unsigned char *buf)
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{
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int i, head_flags;
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int h_id, h_mode, h_sr_index;
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static const int sr_table[4] = { 44100, 48000, 32000, 99999 };
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// get Xing header data
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X->flags = 0; // clear to null incase fail
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// get selected MPEG header data
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h_id = (buf[1] >> 3) & 1;
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h_sr_index = (buf[2] >> 2) & 3;
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h_mode = (buf[3] >> 6) & 3;
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// determine offset of header
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if( h_id ) { // mpeg1
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if( h_mode != 3 ) buf+=(32+4);
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else buf+=(17+4);
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}
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else { // mpeg2
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if( h_mode != 3 ) buf+=(17+4);
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else buf+=(9+4);
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}
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if( buf[0] != 'X' ) return 0; // fail
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if( buf[1] != 'i' ) return 0; // header not found
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if( buf[2] != 'n' ) return 0;
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if( buf[3] != 'g' ) return 0;
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buf+=4;
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X->h_id = h_id;
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X->samprate = sr_table[h_sr_index];
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if( h_id == 0 ) X->samprate >>= 1;
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head_flags = X->flags = ExtractI4(buf); buf+=4; // get flags
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if( head_flags & FRAMES_FLAG ) {X->frames = ExtractI4(buf); buf+=4;}
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if( head_flags & BYTES_FLAG ) {X->bytes = ExtractI4(buf); buf+=4;}
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if( head_flags & TOC_FLAG ) {
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if( X->toc != NULL ) {
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for(i=0;i<100;i++) X->toc[i] = buf[i];
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}
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buf+=100;
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}
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X->vbr_scale = -1;
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if( head_flags & VBR_SCALE_FLAG ) {X->vbr_scale = ExtractI4(buf); buf+=4;}
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//if( X->toc != NULL ) {
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//for(i=0;i<100;i++) {
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// if( (i%10) == 0 ) printf("\n");
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// printf(" %3d", (int)(X->toc[i]));
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//}
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//}
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return 1; // success
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}
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/*-------------------------------------------------------------*/
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int SeekPoint(unsigned char TOC[100], int file_bytes, float percent)
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{
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// interpolate in TOC to get file seek point in bytes
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int a, seekpoint;
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float fa, fb, fx;
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if( percent < 0.0f ) percent = 0.0f;
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if( percent > 100.0f ) percent = 100.0f;
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a = (int)percent;
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if( a > 99 ) a = 99;
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fa = TOC[a];
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if( a < 99 ) {
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fb = TOC[a+1];
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}
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else {
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fb = 256.0f;
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}
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fx = fa + (fb-fa)*(percent-a);
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//printf("%f ....... %f ...... %f\n",fa,fb,fx);
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seekpoint = (int)((1.0f/256.0f)*fx*file_bytes);
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return seekpoint;
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}
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/*-------------------------------------------------------------*/
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