/* 
 * stripsil.c (c) 2001 Petr Tomasek <tomasek@etf.cuni.cz>
 * (See http://www.etf.cuni.cz/~tomasek/)
 *
 * Strips silence from .wav stream (I use it for digitialize some old
 * tapes into mp3)..
 *
 *  usage:  stripsil < in.wav > out.wav
 *
 *  compile: gcc stripsil.c -o stripsil -lm
 *
 */

#include <stdio.h>
#include <string.h>
#include <math.h>

const int fr=10; /*  1/fr s ->> rsm */
const int tt=20; /* in frames */
const int trh=750; /* treshhold */
const int trhd=150; /* diference treshhold */

void print_time (FILE *f,long x,long rate)
{
long a,b,c;
a=x/rate;
b=a/60;a=a%60;
c=b/60;c=c%60;
fprintf(f,"%02d:%02d:%02d.%d",c,b,a,(int)(10*(x%rate)/rate));
}

int main () {
#define HEADRLEN 46
unsigned char head[HEADRLEN];
signed char buff[655360];
char h1[5],type[5],ID[5],h2[5];
unsigned long lena,lenh,lend;
unsigned int ftag,ch,samp,bps,balign,spec,bytes,bits;
int byts;

signed long a1,a2,m1,m2,mm1,mm2,md1,md2;
double sum1,sum2,sumd1,sumd2;
int i,n=0;
int nn,ii,nx;
signed long b1,b2,d1,d2;

size_t rd;

int silent=1,sc=0;

fprintf(stderr,"Stripsil: (c) 2001 Petr Tomasek <tomasek@etf.cuni.cz>\n");

#define _GI(q) head[q]+256*head[q+1]
#define _GL(q) head[q]+256*(head[q+1]+256*(head[q+2]+256*head[q+3]))
#define _SS(s,n) \
	s[0]=head[n]; \
	s[1]=head[n+1]; \
	s[2]=head[n+2]; \
	s[3]=head[n+3]; \
	s[4]='\0';

fread(head,1,HEADRLEN,stdin);

_SS(h1,0) _SS(type,8) _SS(ID,12) _SS(h2,36) 
lena=_GL(4); lenh=_GL(16); lend=_GL(40); 
ftag=_GI(20); ch=_GI(22); samp=_GI(24); bps=_GI(26); balign=_GI(28);
	spec=_GI(30); bytes=_GI(32); bits=_GI(34);
byts=bits/8;

if (	(strcmp((char *)h1,"RIFF")) ||
   	(strcmp((char *)type,"WAVE")) ||
	(strcmp((char *)ID,"fmt ")) ||
	(strcmp((char *)h2,"data")) ||
	(lenh!=16) ||
	(!byts) || (byts>2) ||
	(!ch) || (ch>2) ||
	(byts*ch!=bytes) ||
	(ftag!=1) ||
	(samp>48000)
   ) 	{
    fprintf(stderr,"Error: unsupported audio format!!\n");
    exit(-1);

     	}

nn=samp/fr;

fprintf(stderr,"# %u / %d bits / %s /",samp,bits,(ch==1)?"mono":"stereo");
fprintf(stderr,"/ chunk=%u / tt=%u / diff-treshh=%u / treshh=%u \n"
	,nn,tt,trhd,trh);

/*FIXME: set lenght to endless... */
fwrite(head,1,HEADRLEN,stdout);

nx=0;mm1=0;mm2=0;b1=0;b2=0;
rd=1;
while(rd)
{
rd=fread(buff,1,samp*bytes/fr,stdin);
//fprintf(stderr,"<Read : %lu>\n",rd);
 nx+=n;n=0;
 sum1=0;sum2=0;sumd1=0;sumd2=0;
 for (ii=0;ii<nn;ii++)
 {
 a1=buff[n];n++;
  if (byts-1) {a1+=256*buff[n];n++;}
 // else a1=a1-127;
 d1=a1-b1; b1=a1;
 sum1+=a1*a1;
 sumd1+=d1*d1;
 a2=0; if (ch-1)
  {
  a2=buff[n];n++;
   if (byts-1) {a2+=256*buff[n];n++;}
//   else a2=a2-127;
  d2=a2-b2; b2=a2;
  sum2+=a2*a2;
  sumd2+=d2*d2;
  }
 }
 m1=(signed long)sqrt(sum1/nn);
 m2=(signed long)sqrt(sum2/nn);
 md1=(signed long)sqrt(sumd1/nn);
 md2=(signed long)sqrt(sumd2/nn);
// md1=abs(m1-mm1); mm1=m1;
// md2=abs(m2-mm2); mm2=m2;
// printf(" >>%ld %ld <-> %ld %ld\n",m1,m2,md1,md2);
 if (silent)
  {
  if ((m1>=trh) || (m2>=trh) || (md1>=trhd) || (md2>=trhd))
    {
    fprintf(stderr,"Silence END at ");
    print_time(stderr,nx,samp*bytes);
    fprintf(stderr," (%08lx)\n",nx);
    silent=0;sc=0;
    }
  }
else
  if ((md1<trhd) && (md2<trhd))
   {
   sc++;
   if  (sc==tt) 
     {
	fprintf(stderr,"Silence Detected at ");
	print_time(stderr,nx,samp*bytes);
	fprintf(stderr," (%08lx)\n",nx);
	silent=1;
     }
   }
 else sc=0;
if (!silent) fwrite(buff,1,rd,stdout);
}


return  0;
}