1 files changed, 36 insertions, 1 deletions
diff --git a/taglib/mp4/mp4properties.cpp b/taglib/mp4/mp4properties.cpp
index faa43c27..6c6976fa 100644
--- a/taglib/mp4/mp4properties.cpp
+++ b/taglib/mp4/mp4properties.cpp
@@ -31,6 +31,27 @@
 
 using namespace TagLib;
 
+namespace
+{
+  // Calculate the total bytes used by audio data, used to calculate the bitrate
+  long long calculateMdatLength(const MP4::AtomList &list)
+  {
+    long long totalLength = 0;
+    for(MP4::AtomList::ConstIterator it = list.begin(); it != list.end(); ++it) {
+      long length = (*it)->length;
+      if(length == 0)
+        return 0; // for safety, see checkValid() in mp4file.cpp
+
+      if((*it)->name == "mdat")
+        totalLength += length;
+
+      totalLength += calculateMdatLength((*it)->children);
+    }
+
+    return totalLength;
+  }
+}
+
 class MP4::Properties::PropertiesPrivate
 {
 public:
@@ -213,7 +234,14 @@ MP4::Properties::read(File *file, Atoms *atoms)
           pos += 3;
         }
         pos += 10;
-        d->bitrate = static_cast<int>((data.toUInt(pos) + 500) / 1000.0 + 0.5);
+        const unsigned int bitrateValue = data.toUInt(pos);
+        if(bitrateValue != 0 || d->length <= 0) {
+          d->bitrate = static_cast<int>((bitrateValue + 500) / 1000.0 + 0.5);
+        }
+        else {
+          d->bitrate = static_cast<int>(
+                (calculateMdatLength(atoms->atoms) * 8) / d->length);
+        }
       }
     }
   }
@@ -224,6 +252,13 @@ MP4::Properties::read(File *file, Atoms *atoms)
       d->channels      = data.at(73);
       d->bitrate       = static_cast<int>(data.toUInt(80U) / 1000.0 + 0.5);
       d->sampleRate    = data.toUInt(84U);
+
+      if(d->bitrate == 0 && d->length > 0) {
+        // There are files which do not contain a nominal bitrate, e.g. those
+        // generated by refalac64.exe. Calculate the bitrate from the audio
+        // data size (mdat atoms) and the duration.
+        d->bitrate = (calculateMdatLength(atoms->atoms) * 8) / d->length;
+      }
     }
   }