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251 lines
3.5 KiB
251 lines
3.5 KiB
/*---- 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 <unistd.h>
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#include <float.h>
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#include <math.h>
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#include "mpg123/mpg123.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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/*-------------------------------------------------------------*/
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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 mpg123_get_xing_header(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 int sr_table[4] =
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{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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X->toc = NULL;
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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)
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{ /* mpeg1 */
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if (h_mode != 3) {
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buf += (32 + 4);
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}
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else
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buf += (17 + 4);
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}
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else
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{ /* mpeg2 */
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if (h_mode != 3)
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buf += (17 + 4);
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else
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buf += (9 + 4);
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}
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if (buf[0] != 'X')
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return 0; /* fail */
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if (buf[1] != 'i')
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return 0; /* header not found */
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if (buf[2] != 'n')
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return 0;
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if (buf[3] != 'g')
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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)
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X->samprate >>= 1;
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head_flags = X->flags = ExtractI4(buf);
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buf += 4; /* get flags */
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if (head_flags & FRAMES_FLAG)
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{
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X->frames = ExtractI4(buf);
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buf += 4;
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}
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if (head_flags & BYTES_FLAG)
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{
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X->bytes = ExtractI4(buf);
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buf += 4;
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}
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if (head_flags & TOC_FLAG)
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{
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X->toc = malloc(100);
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if (X->toc != NULL)
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{
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for (i = 0; i < 100; i++)
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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)
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{
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X->vbr_scale = ExtractI4(buf);
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buf += 4;
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}
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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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*/
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return 1; /* success */
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}
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/*-------------------------------------------------------------*/
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int mpg123_seek_point(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)
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percent = 0.0f;
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if (percent > 100.0f)
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percent = 100.0f;
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a = (int) percent;
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if (a > 99)
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a = 99;
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fa = TOC[a];
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if (a < 99)
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{
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fb = TOC[a + 1];
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}
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else
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{
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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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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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int mpg123_stream_check_for_xing_header(struct frame *fr, XHEADDATA * xhead)
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{
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unsigned char *head_data;
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int ret;
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lseek(rd->filept, -(fr->framesize + 4), SEEK_CUR);
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head_data = malloc(fr->framesize + 4);
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read(rd->filept,head_data, fr->framesize +4); /* now read the rest */
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ret = mpg123_get_xing_header(xhead, head_data);
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free(head_data);
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return ret;
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}
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