Revert "Revert "Add a tool to inspect audio files, only MP4 is implemented for now""

This reverts commit c6f7ad3e83.

taglib/audioproperties.h

@@ -27,6 +27,7 @@
 #define TAGLIB_AUDIOPROPERTIES_H
 
 #include "taglib_export.h"
+#include "tstring.h"
 
 namespace TagLib {
 
@@ -86,6 +87,8 @@ namespace TagLib {
      */
     virtual int channels() const = 0;
 
+    String toString() const;
+
   protected:
 
     /*!