Opus: Read output gain (#1320)

Author: felipdsa21

taglib/ogg/opus/opusproperties.cpp

@@ -45,6 +45,7 @@ class Opus::Properties::PropertiesPrivate
   int inputSampleRate { 0 };
   int channels { 0 };
   int opusVersion { 0 };
+  int outputGain { 0 };
 };
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -93,6 +94,11 @@ int Opus::Properties::opusVersion() const
   return d->opusVersion;
 }
 
+int Opus::Properties::outputGain() const
+{
+  return d->outputGain;
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // private members
 ////////////////////////////////////////////////////////////////////////////////
@@ -122,9 +128,10 @@ void Opus::Properties::read(File *file)
 
   // *Input Sample Rate* (32 bits, unsigned, little endian)
   d->inputSampleRate = data.toUInt(pos, false);
-  // pos += 4;
+  pos += 4;
 
   // *Output Gain* (16 bits, signed, little endian)
+  d->outputGain = data.toShort(pos, false);
   // pos += 2;
 
   // *Channel Mapping Family* (8 bits, unsigned)

taglib/ogg/opus/opusproperties.h

@@ -80,7 +80,7 @@ namespace TagLib {
          * Returns the sample rate in Hz.
          *
          * \note Always returns 48000, because Opus can decode any stream at a
-         * sample rate of 8, 12, 16, 24, or 48 kHz,
+         * sample rate of 8, 12, 16, 24, or 48 kHz.
          */
         int sampleRate() const override;
 
@@ -101,6 +101,13 @@ namespace TagLib {
          */
         int opusVersion() const;
 
+        /*!
+         * Returns the output gain in signed Q7.8 fixed-point format.
+         *
+         * To convert the value to dB, divide it by 256.0.
+         */
+        int outputGain() const;
+
       private:
         void read(File *file);
 

tests/test_opus.cpp

@@ -58,6 +58,7 @@ class TestOpus : public CppUnit::TestFixture
     CPPUNIT_ASSERT_EQUAL(48000, f.audioProperties()->sampleRate());
     CPPUNIT_ASSERT_EQUAL(48000, f.audioProperties()->inputSampleRate());
     CPPUNIT_ASSERT_EQUAL(1, f.audioProperties()->opusVersion());
+    CPPUNIT_ASSERT_EQUAL(-17920, f.audioProperties()->outputGain());
   }
 
   void testReadComments()