AudioFrame: refactor how to get a default number of samples

Clement Champetier · Clement Champetier · commit 249bcfbc67b4 · 2016-11-02T09:39:33.000+01:00
* Add a private method.
* Add doc about this tricky case.
diff --git a/src/AvTranscoder/data/decoded/AudioFrame.cpp b/src/AvTranscoder/data/decoded/AudioFrame.cpp
@@ -49,7 +49,7 @@ AudioFrame::AudioFrame(const AudioFrameDesc& desc, const bool forceDataAllocatio
     av_frame_set_channels(_frame, desc._nbChannels);
     av_frame_set_channel_layout(_frame, av_get_default_channel_layout(desc._nbChannels));
     _frame->format = desc._sampleFormat;
-    _frame->nb_samples = desc._sampleRate / 25.; // cannot be known before calling avcodec_decode_audio4
+    _frame->nb_samples = getDefaultNbSamples();
 
     if(forceDataAllocation)
         allocateData();
@@ -103,7 +103,7 @@ void AudioFrame::allocateData()
     av_frame_set_channels(_frame, _desc._nbChannels);
     av_frame_set_channel_layout(_frame, av_get_default_channel_layout(_desc._nbChannels));
     _frame->format = _desc._sampleFormat;
-    _frame->nb_samples = _desc._sampleRate / 25.; // cannot be known before calling avcodec_decode_audio4
+    _frame->nb_samples = getDefaultNbSamples();
 
     // Allocate data
     const int align = 0;
@@ -143,4 +143,10 @@ void AudioFrame::assignBuffer(const unsigned char* ptrValue)
         throw std::runtime_error(os.str());
     }
 }
+
+size_t AudioFrame::getDefaultNbSamples() const
+{
+    return _desc._sampleRate / 25.;
+}
+
 }
diff --git a/src/AvTranscoder/data/decoded/AudioFrame.hpp b/src/AvTranscoder/data/decoded/AudioFrame.hpp
@@ -67,6 +67,17 @@ class AvExport AudioFrame : public IFrame
 
     void assignBuffer(const unsigned char* ptrValue);
 
+private:
+    /**
+     * @brief The number of samples of a frame cannot be known before calling avcodec_decode_audio4,
+     * and can be variable in a same stream. Because we need to allocate some frames without knowing this parameter,
+     * we access here a default number of samples.
+     * @note This value depends on the sample rate (excample: 1920 samples at 48kHz).
+     * @return the number of samples of our default AudioFrame.
+     * @see setNbSamplesPerChannel
+     */
+    size_t getDefaultNbSamples() const;
+
 private:
     /**
      * @brief Description of the frame to allocate.
