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wav: get sample count from fact chunk if present

--- a/src/wav.c

+++ b/src/wav.c

@@ -824,6 +824,20 @@

             goto next;

         }

+        if (!memcmp(magic, "fact", 4)) {

+            uint32_t val;

+

+            if (clen < 4) {

+                lsx_fail_errno(ft, SOX_EHDR, "fact chunk too small");

+                return SOX_EOF;

+            }

+

+            lsx_readdw(ft, &val);

+            wav->numSamples = val;

+

+            goto next;

+        }

+

         if (!memcmp(magic, "data", 4)) {

             if (isRF64 && clen == UINT32_MAX)

                 clen = ds64_data_size;

@@ -875,7 +889,12 @@

     if (ft->seekable)

         lsx_seeki(ft, wav->dataStart, SEEK_SET);

-    if (qwDataLength == UINT32_MAX || qwDataLength == MS_UNSPEC) {

+    /* some files wrongly report total samples across all channels */

+    if (wav->numSamples * wav->blockAlign == qwDataLength * ft->signal.channels)

+        wav->numSamples /= ft->signal.channels;

+

+    if ((qwDataLength == UINT32_MAX && !wav->numSamples) ||

+        qwDataLength == MS_UNSPEC) {

         lsx_warn("WAV data length is magic value or UINT32_MAX, ignoring");

         wav->ignoreSize = 1;

     }

@@ -911,7 +930,8 @@

         break;

     default:

-        wav->numSamples = div_bits(qwDataLength, ft->encoding.bits_per_sample) / ft->signal.channels;

+        if (!wav->numSamples)

+            wav->numSamples = div_bits(qwDataLength, ft->encoding.bits_per_sample) / ft->signal.channels;

         ft->signal.length = wav->numSamples * ft->signal.channels;

     }