Fix channel layout reporting for implicit signalling of AAC parametric stereo

media/mp4/aac.cc

Index: media/mp4/aac.cc
diff --git a/media/mp4/aac.cc b/media/mp4/aac.cc
index f7826363b80d8b0f92631676ecfbee1a83e67da7..f92dd2feb928b9fc69cf1e9c6337c1bb19f513dd 100644
--- a/media/mp4/aac.cc
+++ b/media/mp4/aac.cc
@@ -19,7 +19,7 @@ static const int kFrequencyMap[] = {
 
 namespace media {
 
-static ChannelLayout GetChannelLayout(uint8 channel_config) {
+static ChannelLayout ConvertChannelConfigToLayout(uint8 channel_config) {
   switch (channel_config) {
     case 1:
       return CHANNEL_LAYOUT_MONO;
@@ -130,9 +130,9 @@ bool AAC::Parse(const std::vector<uint8>& data) {
 
   // When Parametric Stereo is on, mono will be played as stereo.
   if (ps_present && channel_config_ == 1)
-    channel_layout_ = GetChannelLayout(2);
+    channel_layout_ = CHANNEL_LAYOUT_STEREO;
   else
-    channel_layout_ = GetChannelLayout(channel_config_);
+    channel_layout_ = ConvertChannelConfigToLayout(channel_config_);
 
   return frequency_ != 0 && channel_layout_ != CHANNEL_LAYOUT_UNSUPPORTED &&
       profile_ >= 1 && profile_ <= 4 && frequency_index_ != 0xf &&
@@ -154,7 +154,13 @@ int AAC::GetOutputSamplesPerSecond(bool sbr_in_mimetype) const {
   return std::min(2 * frequency_, 48000);
 }
 
-ChannelLayout AAC::channel_layout() const {
+ChannelLayout AAC::GetChannelLayout(bool sbr_in_mimetype) const {
+  // Check for implicit signalling of HE-AAC and indicate stereo output
+  // if the mono channel configuration is signalled.
+  // See ISO-14496-3 Section 1.6.6.1.2 for details about this special casing.
+  if (sbr_in_mimetype && channel_config_ == 1)
+    return CHANNEL_LAYOUT_STEREO;
+
   return channel_layout_;
 }