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/* this file is a part of amp software, (C) tomislav uzelac 1996,1997
*/
/* layer3.c layer3 audio decoding
*
* Created by: tomislav uzelac Mar 1 97
* Last modified by:
*/
#include "amp.h"
#include "audio.h"
#include "dump.h"
#include "getbits.h"
#include "getdata.h"
#include "huffman.h"
#include "misc2.h"
#include "rtbuf.h"
#include "transform.h"
#define LAYER3
#include "layer3.h"
/* this function decodes one layer3 audio frame, except for the header decoding
* which is done in main() [audio.c]. returns 0 if everything is ok.
*/
int layer3_frame(struct AUDIO_HEADER *header,int cnt)
{
static struct SIDE_INFO info;
int gr,ch,sb,i;
int mean_frame_size,bitrate,fs,hsize,ssize;
/* we need these later, hsize is the size of header+side_info
*/
if (header->ID)
if (header->mode==3) {
nch=1;
hsize=21;
} else {
nch=2;
hsize=36;
}
else
if (header->mode==3) {
nch=1;
hsize=13;
} else {
nch=2;
hsize=21;
}
/* crc increases hsize by 2
*/
if (header->protection_bit==0) hsize+=2;
/* read layer3 specific side_info
*/
getinfo(header,&info);
/* MPEG2 only has one granule
*/
bitrate=t_bitrate[header->ID][3-header->layer][header->bitrate_index];
fs=t_sampling_frequency[header->ID][header->sampling_frequency];
if (header->ID) mean_frame_size=144000*bitrate/fs;
else mean_frame_size=72000*bitrate/fs;
/* check if mdb is too big for the first few frames. this means that
* a part of the stream could be missing. We must still fill the buffer
*
* don't forget to (re)initialise bclean_bytes to 0, and f_bdirty to FALSE!!!
*/
if (f_bdirty)
if (info.main_data_begin > bclean_bytes) {
fillbfr(mean_frame_size + header->padding_bit - hsize);
bclean_bytes+=mean_frame_size + header->padding_bit - hsize;
/* warn(" frame %d discarded, incomplete main_data\n",cnt); */
return 0;
} else {
/* re-initialise */
f_bdirty=FALSE;
bclean_bytes=0;
}
/* now update the data 'pointer' (counting in bits) according to
* the main_data_begin information
*/
data = 8 * ((append - info.main_data_begin) & (BUFFER_SIZE-1));
/* read into the buffer all bytes up to the start of next header
*/
fillbfr(mean_frame_size + header->padding_bit - hsize);
/* these two should go away
*/
t_l=&t_b8_l[header->ID][header->sampling_frequency][0];
t_s=&t_b8_s[header->ID][header->sampling_frequency][0];
/* debug/dump stuff
*/
if (A_DUMP_BINARY) dump((int *)info.part2_3_length);
/* decode the scalefactors and huffman data
* this part needs to be enhanced for error robustness
*/
for (gr=0;gr < ((header->ID) ? 2 : 1);gr++) {
for (ch=0;ch<nch;ch++) {
ssize=decode_scalefactors(&info,header,gr,ch);
decode_huffman_data(&info,gr,ch,ssize);
}
/* requantization, stereo processing, reordering(shortbl)
*/
if (A_DOWNMIX && nch==2) requantize_downmix(gr,&info,header);
else
if (header->mode!=1 || (header->mode==1 && header->mode_extension==0))
for (ch=0;ch<nch;ch++) requantize_mono(gr,ch,&info,header);
else requantize_ms(gr,&info,header);
/* just which window?
*/
/* this is a very temporary, very ugly hack.
*/
if (A_DOWNMIX) nch=1;
for (ch=0; ch < (A_DOWNMIX ? 1:nch) ;ch++) {
int win_type; /* same as in the standard, long=0, start=1 ,.... */
int window_switching_flag = info.window_switching_flag[gr][ch];
int block_type = info.block_type[gr][ch];
int mixed_block_flag = info.mixed_block_flag[gr][ch];
/* antialiasing butterflies
*/
if (!(window_switching_flag &&
block_type==2))
alias_reduction(ch);
if (window_switching_flag &&
block_type==2 &&
mixed_block_flag)
win_type=0;
else
if (!window_switching_flag) win_type=0;
else win_type=block_type;
/* imdct ...
*/
for (sb=0;sb<2;sb++)
imdct(win_type,sb,ch);
if (window_switching_flag &&
block_type==2 &&
mixed_block_flag)
win_type=2;
/* no_of_imdcts tells us how many subbands from the top are all zero
* it is set by the requantize functions in misc2.c
*/
for (sb=2;sb<no_of_imdcts[ch];sb++)
imdct(win_type,sb,ch);
for (;sb<32;sb++)
for (i=0;i<18;i++) {
res[sb][i]=s[ch][sb][i];
s[ch][sb][i]=0.0f;
}
/* polyphase filterbank
*/
/* if (nch == 2) this was a bug, tomislav */
for (i=0;i<18;i++)
poly(ch,i);
}
printout();
/* this is part2 of a particularily ugly hack. this should vanish as soon as nch isn't
a global variable anymore
*/
if (A_DOWNMIX && header->mode!=3) nch=2;
} /* for (gr... */
/* return status: 0 for ok, errors will be added
*/
return 0;
}
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