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AMR file duration

--- a/src/amr.h

+++ b/src/amr.h

@@ -90,6 +90,7 @@

 {

   int open_library_result;

+  (void)encoding;

 #ifdef AMR_OPENCORE

   if (AMR_OPENCORE_ENABLE_ENCODE || !encoding)

   {

@@ -151,6 +152,24 @@

 #endif

 }

+static size_t amr_duration_frames(sox_format_t * ft)

+{

+  off_t      frame_size, data_start_offset = lsx_tell(ft);

+  size_t     frames;

+  uint8_t    coded;

+

+  for (frames = 0; lsx_readbuf(ft, &coded, (size_t)1) == 1; ++frames) {

+    frame_size = amr_block_size[coded >> 3 & 15];

+    if (lsx_seeki(ft, frame_size - 1, SEEK_CUR)) {

+      lsx_fail("seek");

+      break;

+    }

+  }

+  lsx_debug("frames=%lu", (unsigned long)frames);

+  lsx_seeki(ft, data_start_offset, SEEK_SET);

+  return frames;

+}

+

 static int startread(sox_format_t * ft)

 {

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

@@ -180,6 +199,8 @@

   ft->signal.rate = AMR_RATE;

   ft->encoding.encoding = AMR_ENCODING;

   ft->signal.channels = 1;

+  ft->signal.length = ft->signal.length != SOX_IGNORE_LENGTH && ft->seekable?

+    (size_t)(amr_duration_frames(ft) * .02 * ft->signal.rate +.5) : SOX_UNSPEC;

   return SOX_SUCCESS;

 }