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104 lines
3 KiB
C++
104 lines
3 KiB
C++
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/* this file is a part of amp software, (C) tomislav uzelac 1996,1997
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*/
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/* position.c ffwd/rew within a stream
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*
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* Creted by: Tomislav Uzelac, May 10 1997
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*/
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#include <stdlib.h>
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#include <string.h>
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#include "amp.h"
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#include "audio.h"
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#include "getbits.h"
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#define POSITION
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#include "position.h"
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/* Returns the number of frames actually skipped, -1 on error.
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*
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* Values in header are not changed if retval!=nframes.
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* This is not necessary because gethdr() doesn't clobber
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* the contents of header, but I don't want to rely on that.
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*/
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int ffwd(struct AUDIO_HEADER *header, int nframes)
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{
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int cnt=0,g;
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int hsize,bitrate,fs,mean_frame_size;
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struct AUDIO_HEADER tmp;
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memcpy(&tmp,header,sizeof(tmp));
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while (cnt < nframes) {
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if (tmp.ID)
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if (tmp.mode==3) hsize=21;
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else hsize=36;
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else
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if (tmp.mode==3) hsize=13;
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else hsize=21;
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if (tmp.protection_bit==0) hsize+=2;
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if ((g=dummy_getinfo(hsize))) /* dummy_getinfo: reads hsize-4 bytes */
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switch (g) {
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case GETHDR_EOF: return cnt;
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case GETHDR_ERR:
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default: return -1;
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}
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bitrate=t_bitrate[tmp.ID][3-tmp.layer][tmp.bitrate_index];
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fs=t_sampling_frequency[tmp.ID][tmp.sampling_frequency];
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if (tmp.ID) mean_frame_size=144000*bitrate/fs;
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else mean_frame_size=72000*bitrate/fs;
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fillbfr(mean_frame_size + tmp.padding_bit - hsize);
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if ((g=gethdr(&tmp)))
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switch (g) {
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case GETHDR_EOF: return cnt;
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case GETHDR_ERR:
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default: return -1;
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}
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cnt++;
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}
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memcpy(header,&tmp,sizeof(tmp));
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return cnt;
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}
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/* Mostly the same as ffwd. Some streams might be 'tough', i.e.
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* the ones switching bitrates.
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*/
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int rew(struct AUDIO_HEADER *header, int nframes)
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{
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int cnt=0;
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int bitrate,fs,mean_frame_size;
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struct AUDIO_HEADER tmp;
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memcpy(&tmp,header,sizeof(tmp));
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while (cnt < nframes) {
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/* ffwd/rew functions are to be called right after the header has been parsed
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* so we have to go back one frame + 4 bytes + 1 byte (in case padding was used).
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*/
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bitrate=t_bitrate[tmp.ID][3-tmp.layer][tmp.bitrate_index];
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fs=t_sampling_frequency[tmp.ID][tmp.sampling_frequency];
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if (tmp.ID) mean_frame_size=144000*bitrate/fs;
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else mean_frame_size=72000*bitrate/fs;
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if (rewind_stream(mean_frame_size) !=0) {
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memcpy(header,&tmp,sizeof(tmp));
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return cnt;
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}
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if ((gethdr(&tmp))) return -1;
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cnt++;
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}
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/* We have to make sure that the bit reservoir contains enough data.
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* Hopefully, layer3_frame will take care of that.
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*/
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f_bdirty=TRUE;
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bclean_bytes=0;
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memcpy(header,&tmp,sizeof(tmp));
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return cnt;
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}
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/* TODO: after the gethdr function is enhanced with the counter to count
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* the number of bytes to search for the next syncword, make the call to
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* gethdr() from rew() have that counter something like (frame_size-1) so
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* that we don't go back again and again to the same header. (not very important)
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*/
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