Re-add AC3/EAC3 audio demuxing support

net/base/mime_util.cc

Index: net/base/mime_util.cc
diff --git a/net/base/mime_util.cc b/net/base/mime_util.cc
index e4901277c3f8c12e9207a83deddfeee0fa09ad71..d8a714c00cec2522ad7b6c89a93c1237a1a5ecfe 100644
--- a/net/base/mime_util.cc
+++ b/net/base/mime_util.cc
@@ -48,6 +48,11 @@ class MimeUtil : public PlatformMimeUtil {
     VP8,
     VP9,
     THEORA
+#if defined(ENABLE_AC3_EAC3_AUDIO_DEMUXING)
+    ,
+    AC3,
+    EAC3
+#endif
   };
 
   bool GetMimeTypeFromExtension(const base::FilePath::StringType& ext,
@@ -472,6 +477,13 @@ static bool IsCodecSupportedOnAndroid(MimeUtil::Codec codec) {
       // MPEG-2 variants of AAC are not supported on Android.
       return false;
 
+#if defined(ENABLE_AC3_EAC3_AUDIO_DEMUXING)
+    case MimeUtil::AC3:
+    case MimeUtil::EAC3:
+      // TODO(servolk): Revisit this for AC3/EAC3 support on AndroidTV
+      return false;
+#endif
+
     case MimeUtil::VP9:
       // VP9 is supported only in KitKat+ (API Level 19).
       return base::android::BuildInfo::GetInstance()->sdk_int() >= 19;
@@ -521,6 +533,11 @@ struct MediaFormatStrict {
 //   avc1.6400xx - H.264 High
 static const char kMP4AudioCodecsExpression[] =
     "mp4a.66,mp4a.67,mp4a.68,mp4a.69,mp4a.6B,mp4a.40.2,mp4a.40.02,mp4a.40.5,"
+#if defined(ENABLE_AC3_EAC3_AUDIO_DEMUXING)
+    "ac-3,ec-3,"  // Note: only one variant of eac codec string is sufficient
+                  // here since these are converted into enums in
+                  // InitializeMimeTypeMaps
+#endif
     "mp4a.40.05,mp4a.40.29";
 static const char kMP4VideoCodecsExpression[] =
     // This is not a complete list of supported avc1 codecs. It is simply used
@@ -530,6 +547,11 @@ static const char kMP4VideoCodecsExpression[] =
     // kUnambiguousCodecStringMap/kAmbiguousCodecStringMap should be the only
     // mapping from strings to codecs. See crbug.com/461009.
     "avc1.42E00A,avc1.4D400A,avc1.64000A,"
+#if defined(ENABLE_AC3_EAC3_AUDIO_DEMUXING)
+    "ac-3,ec-3,"  // Note: only one variant of eac codec string is sufficient
+                  // here since these are converted into enums in
+                  // InitializeMimeTypeMaps
+#endif
     "mp4a.66,mp4a.67,mp4a.68,mp4a.69,mp4a.6B,mp4a.40.2,mp4a.40.02,mp4a.40.5,"
     "mp4a.40.05,mp4a.40.29";
 
@@ -583,6 +605,12 @@ static const CodecIDMappings kUnambiguousCodecStringMap[] = {
     {"mp4a.40.5", MimeUtil::MPEG4_AAC_SBR_v1},
     {"mp4a.40.05", MimeUtil::MPEG4_AAC_SBR_v1},
     {"mp4a.40.29", MimeUtil::MPEG4_AAC_SBR_PS_v2},
+#if defined(ENABLE_AC3_EAC3_AUDIO_DEMUXING)
+    {"ac-3", MimeUtil::AC3},
+    {"ec-3", MimeUtil::EAC3},
+    {"mp4a.a5", MimeUtil::AC3},
+    {"mp4a.a6", MimeUtil::EAC3},
+#endif
     {"vorbis", MimeUtil::VORBIS},
     {"opus", MimeUtil::OPUS},
     {"vp8", MimeUtil::VP8},
@@ -908,6 +936,13 @@ void MimeUtil::ParseCodecString(const std::string& codecs,
   for (std::vector<std::string>::iterator it = codecs_out->begin();
        it != codecs_out->end();
        ++it) {
+#if defined(ENABLE_AC3_EAC3_AUDIO_DEMUXING)
+    // We need to know the codec subtype to properly support AC3/EAC3.
+    // Do not strip the first '.' for mp4a.a5 and mp4a.a6.
+    if (it->compare("mp4a.a5") == 0 || it->compare("mp4a.a6") == 0) {
+      continue;
+    }
+#endif
     size_t found = it->find_first_of('.');
     if (found != std::string::npos)
       it->resize(found);
@@ -1084,6 +1119,10 @@ bool MimeUtil::IsCodecProprietary(Codec codec) const {
     case H264_BASELINE:
     case H264_MAIN:
     case H264_HIGH:
+#if defined(ENABLE_AC3_EAC3_AUDIO_DEMUXING)
+    case AC3:
+    case EAC3:
+#endif
       return true;
 
     case PCM: