shithub: sox

Info  •  Files  •  Log  •  Branches

mp3: fix duration calculation

Avoid rounding errors as much as possible.  It is still possible for
the CBR extrapolation to be slightly off.

--- a/src/mp3-util.h

+++ b/src/mp3-util.h

@@ -249,22 +249,16 @@

   return 0;

 }

-static void mad_timer_mult(mad_timer_t * t, double d)

+static size_t mp3_duration(sox_format_t * ft)

 {

-  t->seconds = (signed long)(d *= (t->seconds + t->fraction * (1. / MAD_TIMER_RESOLUTION)));

-  t->fraction = (unsigned long)((d - t->seconds) * MAD_TIMER_RESOLUTION + .5);

-}

-

-static size_t mp3_duration_ms(sox_format_t * ft)

-{

   priv_t              * p = (priv_t *) ft->priv;

   struct mad_stream   mad_stream;

   struct mad_header   mad_header;

   struct mad_frame    mad_frame;

-  mad_timer_t         time = mad_timer_zero;

   size_t              initial_bitrate = 0; /* Initialised to prevent warning */

   size_t              tagsize = 0, consumed = 0, frames = 0;

   sox_bool            vbr = sox_false, depadded = sox_false;

+  size_t              num_samples = 0;

   p->mad_stream_init(&mad_stream);

   p->mad_header_init(&mad_header);

@@ -309,7 +303,7 @@

         continue; /* Not an audio frame */

       }

-      p->mad_timer_add(&time, mad_header.duration);

+      num_samples += MAD_NSBSAMPLES(&mad_header) * 32;

       consumed += mad_stream.next_frame - mad_stream.this_frame;

       lsx_debug_more("bitrate=%lu", mad_header.bitrate);

@@ -324,7 +318,7 @@

             break;

           }

         if ((frames = xing_frames(p, mad_stream.anc_ptr, mad_stream.anc_bitlen))) {

-          p->mad_timer_multiply(&time, (signed long)frames);

+          num_samples *= frames;

           lsx_debug("got exact duration from XING frame count (%" PRIuPTR ")", frames);

           break;

         }

@@ -333,7 +327,9 @@

       /* If not VBR, we can time just a few frames then extrapolate */

       if (++frames == 25 && !vbr) {

-        mad_timer_mult(&time, (double)(lsx_filelength(ft) - tagsize) / consumed);

+        double frame_size = (double) consumed / frames;

+        size_t num_frames = (lsx_filelength(ft) - tagsize) / frame_size;

+        num_samples = num_samples / frames * num_frames;

         lsx_debug("got approx. duration by CBR extrapolation");

         break;

       }

@@ -344,7 +340,8 @@

   mad_header_finish(&mad_header);

   p->mad_stream_finish(&mad_stream);

   lsx_rewind(ft);

-  return p->mad_timer_count(time, MAD_UNITS_MILLISECONDS);

+

+  return num_samples;

 }

 #endif /* HAVE_MAD_H */

--- a/src/mp3.c

+++ b/src/mp3.c

@@ -391,7 +391,7 @@

     if (!ft->signal.length)

 #endif

       if (!ignore_length)

-        ft->signal.length = mp3_duration_ms(ft);

+        ft->signal.length = mp3_duration(ft);

   }

   p->mad_stream_init(&p->Stream);

@@ -466,7 +466,6 @@

   if (ignore_length)

     ft->signal.length = SOX_UNSPEC;

   else {

-    ft->signal.length = (uint64_t)(ft->signal.length * .001 * ft->signal.rate + .5);

     ft->signal.length *= ft->signal.channels;  /* Keep separate from line above! */

   }