Fix channel layout reporting for implicit signalling of AAC parametric stereo

media/mp4/aac.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "media/mp4/aac.h"
 
 #include <algorithm>
 
 #include "base/logging.h"
 #include "media/base/bit_reader.h"
 #include "media/mp4/rcheck.h"
 
 // The following conversion table is extracted from ISO 14496 Part 3 -
 // Table 1.16 - Sampling Frequency Index.
 static const int kFrequencyMap[] = {
   96000, 88200, 64000, 48000, 44100, 32000, 24000,
   22050, 16000, 12000, 11025, 8000, 7350
 };
 
 namespace media {
 
-static ChannelLayout GetChannelLayout(uint8 channel_config) {
+static ChannelLayout ConvertChannelConfigToLayout(uint8 channel_config) {
   switch (channel_config) {
     case 1:
       return CHANNEL_LAYOUT_MONO;
     case 2:
       return CHANNEL_LAYOUT_STEREO;
     case 3:
       return CHANNEL_LAYOUT_SURROUND;
     case 4:
       return CHANNEL_LAYOUT_4_0;
     case 5:
@@ skipping 90 matching lines @@
     frequency_ = kFrequencyMap[frequency_index_];
   }
 
   if (extension_frequency_ == 0 && extension_frequency_index != 0xff) {
     RCHECK(extension_frequency_index < arraysize(kFrequencyMap));
     extension_frequency_ = kFrequencyMap[extension_frequency_index];
   }
 
   // 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 &&
       channel_config_ <= 7;
 }
 
 int AAC::GetOutputSamplesPerSecond(bool sbr_in_mimetype) const {
   if (extension_frequency_ > 0)
     return extension_frequency_;
 
   if (!sbr_in_mimetype)
     return frequency_;
 
   // The following code is written according to ISO 14496 Part 3 Table 1.11 and
   // Table 1.22. (Table 1.11 refers to the capping to 48000, Table 1.22 refers
   // to SBR doubling the AAC sample rate.)
   // TODO(acolwell) : Extend sample rate cap to 96kHz for Level 5 content.
   DCHECK_GT(frequency_, 0);
   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_;
 }
 
 bool AAC::ConvertEsdsToADTS(std::vector<uint8>* buffer) const {
   size_t size = buffer->size() + kADTSHeaderSize;
 
   DCHECK(profile_ >= 1 && profile_ <= 4 && frequency_index_ != 0xf &&
          channel_config_ <= 7);
 
   // ADTS header uses 13 bits for packet size.
@@ skipping 89 matching lines @@
 
     RCHECK(bit_reader->ReadBits(1, &dummy));  // extensionFlag3
   }
 
   return true;
 }
 
 }  // namespace mp4
 
 }  // namespace media