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audio/oggdec: add -s SECONDS option to seek before decoding

--- a/sys/src/cmd/audio/oggdec/oggdec.c

+++ b/sys/src/cmd/audio/oggdec/oggdec.c

@@ -27,6 +27,9 @@

 #include <math.h>

 #include <vorbis/codec.h>

 #include <sys/wait.h>

+#define _PLAN9_SOURCE

+#include <utf.h>

+#include <lib9.h>

 static int ifd = -1;

@@ -95,7 +98,14 @@

 		write(ifd, buf, n);

 }

-int main(){

+void

+usage(void)

+{

+	fprintf(stderr, "usage: %s [-s SECONDS]\n", argv0);

+	exit(1);

+}

+

+int main(int argc, char **argv){

   ogg_sync_state   oy; /* sync and verify incoming physical bitstream */

   ogg_stream_state os; /* take physical pages, weld into a logical

 			  stream of packets */

@@ -110,8 +120,25 @@

   char *buffer;

   int  bytes;

-  int  status;

+  int  status, n;

+  long   seeking, seekoff = 4096;

+  double seek, left, right, time, lasttime;

+

+  seek = 0.0;

+  ARGBEGIN{

+  case 's':

+  	seek = atof(EARGF(usage()));

+  	seeking = 1;

+  	if(seek > 0.0)

+  	  break;

+  default:

+    usage();

+  }ARGEND;

+

+  lasttime = left = 0.0;

+  right = seek;

+

   /********** Decode setup ************/

   ogg_sync_init(&oy); /* Now we can read pages */

@@ -134,7 +161,6 @@

     if(ogg_sync_pageout(&oy,&og)!=1){

       /* have we simply run out of data?  If so, we're done. */

       if(bytes<4096)break;

-      

       /* error case.  Must not be Vorbis data */

       fprintf(stderr,"Input does not appear to be an Ogg bitstream.\n");

       exit(1);

@@ -241,7 +267,7 @@

 				       proceed in parallel.  We could init

 				       multiple vorbis_block structures

 				       for vd here */

-    

+

     /* The rest is just a straight decode loop until end of stream */

     while(!eos){

       while(!eos){

@@ -248,7 +274,8 @@

 	int result=ogg_sync_pageout(&oy,&og);

 	if(result==0)break; /* need more data */

 	if(result<0){ /* missing or corrupt data at this page position */

-	  fprintf(stderr,"Corrupt or missing data in bitstream; "

+	  if(!seeking)

+	    fprintf(stderr,"Corrupt or missing data in bitstream; "

 		  "continuing...\n");

 	}else{

 	  if(ogg_page_bos(&og)){ /* got new start of stream */

@@ -261,6 +288,7 @@

 	  }

 	  ogg_stream_pagein(&os,&og); /* can safely ignore errors at

 					 this point */

+

 	  while(1){

 	    result=ogg_stream_packetout(&os,&op);

@@ -268,6 +296,28 @@

 	    if(result<0){ /* missing or corrupt data at this page position */

 	      /* no reason to complain; already complained above */

 	    }else{

+	      if(seeking){

+	        time = vorbis_granule_time(&vd, ogg_page_granulepos(&og));

+	        if(time > left && time < right && time - lasttime > 0.1){

+	          if(time > seek)

+	            right = time;

+	          else

+	            left = time;

+    	      seekoff *= (seek - time)/(time - lasttime);

+	          if(fabs(right - left) > 1.0 && seekoff >= 4096){

+	            lasttime = time;

+                if((n = fseek(stdin, seekoff, SEEK_CUR)) < 0 && feof(stdin))

+                  n = fseek(stdin, -seekoff/2, SEEK_END);

+                if(n >= 0){

+	      	      ogg_sync_reset(&oy);

+	              ogg_stream_reset(&os);

+                  goto again;

+                }

+              }

+            }

+            seeking = 0;

+            fprintf(stderr, "time: %g\n", time);

+          }

 	      float **pcm;

 	      int samples;

 	      if(vorbis_synthesis(&vb,&op)==0) /* test for success! */

@@ -277,7 +327,7 @@

 		vorbis_synthesis_read(&vd,samples); /* tell libvorbis how

 						   many samples we

 						   actually consumed */

-	      }	    

+	      }

 	    }

 	  }

 	  if(ogg_page_eos(&og))eos=1;

@@ -284,6 +334,7 @@

 	}

       }

       if(!eos){

+again:

 	buffer=ogg_sync_buffer(&oy,4096);

 	bytes=fread(buffer,1,4096,stdin);

 	ogg_sync_wrote(&oy,bytes);