AudioDecoder: improved perf if all channels of the stream are extracted

Clement Champetier · Clement Champetier · commit eb1e9af2bcfa · 2016-07-19T10:09:26.000+02:00
This is the common case of the audio decoding.
diff --git a/src/AvTranscoder/decoder/AudioDecoder.cpp b/src/AvTranscoder/decoder/AudioDecoder.cpp
@@ -118,17 +118,19 @@ bool AudioDecoder::decodeNextFrame(Frame& frameBuffer)
 
 bool AudioDecoder::decodeNextFrame(Frame& frameBuffer, const std::vector<size_t> channelIndexArray)
 {
-    AudioFrame& audioBuffer = static_cast<AudioFrame&>(frameBuffer);
-
-    // decode all data of the next frame
-    AudioFrame allDataOfNextFrame(audioBuffer);
-    if(!decodeNextFrame(allDataOfNextFrame))
-        return false;
-
     AVCodecContext& avCodecContext = _inputStream->getAudioCodec().getAVCodecContext();
     const size_t srcNbChannels = avCodecContext.channels;
     const size_t bytePerSample = av_get_bytes_per_sample((AVSampleFormat)frameBuffer.getAVFrame().format);
 
+    // if all channels of the stream are extracted
+    if(srcNbChannels == channelIndexArray.size())
+        return decodeNextFrame(frameBuffer);
+
+    // else decode all data in an intermediate buffer
+    AudioFrame allDataOfNextFrame(frameBuffer);
+    if(!decodeNextFrame(allDataOfNextFrame))
+        return false;
+
     const int dstNbChannels = 1;
     const int noAlignment = 0;
     const size_t decodedSize = av_samples_get_buffer_size(NULL, dstNbChannels, frameBuffer.getAVFrame().nb_samples,
@@ -153,6 +155,7 @@ bool AudioDecoder::decodeNextFrame(Frame& frameBuffer, const std::vector<size_t>
     }
 
     // copy frame properties of decoded frame
+    AudioFrame& audioBuffer = static_cast<AudioFrame&>(frameBuffer);
     audioBuffer.copyProperties(allDataOfNextFrame);
     av_frame_set_channels(&audioBuffer.getAVFrame(), channelIndexArray.size());
     av_frame_set_channel_layout(&audioBuffer.getAVFrame(), av_get_default_channel_layout(channelIndexArray.size()));
