fix sample rate in mp4a box

Author: chemag

ISOBMFF/include/ISOBMFF/MP4A.hpp

@@ -58,11 +58,12 @@ namespace ISOBMFF
 
             uint16_t GetChannelCount() const;
             uint16_t GetSampleSize() const;
-            uint32_t GetSampleRate() const;
+            uint32_t GetSampleRateRaw() const;
+            float GetSampleRate() const;
 
             void SetChannelCount( uint16_t value );
             void SetSampleSize( uint16_t value );
-            void SetSampleRate( uint32_t value );
+            void SetSampleRateRaw( uint32_t value );
 
             void                                  AddBox( std::shared_ptr< Box > box ) override;
             std::vector< std::shared_ptr< Box > > GetBoxes() const override;

ISOBMFF/source/MP4A.cpp

@@ -111,8 +111,7 @@ namespace ISOBMFF
         stream.ReadUInt16();
 
         // template unsigned int(32) samplerate = { default samplerate of media } << 16;
-        uint32_t sampleRateFixed =  stream.ReadBigEndianUInt32();
-        SetSampleRate( (sampleRateFixed >> 16) + ((sampleRateFixed & 0xFFFF) / 65536) );
+        SetSampleRateRaw( stream.ReadBigEndianUInt32() );
 
         container.ReadData( parser, stream );
         this->impl->_boxes = container.GetBoxes();
@@ -124,6 +123,7 @@ namespace ISOBMFF
 
         props.push_back( { "Channel Count", std::to_string(this->GetChannelCount()) } );
         props.push_back( { "Sample Size", std::to_string(this->GetSampleSize()) } );
+        props.push_back( { "Sample Rate (raw)", std::to_string(this->GetSampleRateRaw()) } );
         props.push_back( { "Sample Rate", std::to_string(this->GetSampleRate()) } );
 
         return props;
@@ -145,11 +145,25 @@ namespace ISOBMFF
         return this->impl->_samplesize;
     }
 
-    uint32_t MP4A::GetSampleRate() const
+    uint32_t MP4A::GetSampleRateRaw() const
     {
         return this->impl->_samplerate;
     }
 
+    float MP4A::GetSampleRate() const
+    {
+        uint32_t sampleRateFixed =  this->GetSampleRateRaw();
+        // Read Sample Rate:
+        // The sample rate is stored as a 16.16 fixed-point number (32 bits).
+        // The integer part is obtained by shifting the value right by 16 bits
+        // (>> 16).
+        float sampleRate = (sampleRateFixed >> 16);
+        // The fractional part is obtained by masking the lower 16 bits
+        // (& 0xFFFF) and dividing by 65536.0.
+        sampleRate += ((sampleRateFixed & 0xffff) / 65536.0);
+        return sampleRate;
+    }
+
     void MP4A::SetChannelCount( uint16_t channelcount )
     {
         this->impl->_channelcount = channelcount;
@@ -160,7 +174,7 @@ namespace ISOBMFF
         this->impl->_samplesize = samplesize;
     }
 
-    void MP4A::SetSampleRate( uint32_t samplerate )
+    void MP4A::SetSampleRateRaw( uint32_t samplerate )
     {
         this->impl->_samplerate = samplerate;
     }