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 cba37a452b78662f3304120741f1ad840046010c..c2065622518d51611228d7226675d0e9bb48d304 100644
--- a/net/base/mime_util.cc
+++ b/net/base/mime_util.cc
@@ -69,6 +69,11 @@ class MimeUtil : public PlatformMimeUtil {
     VP8,
     VP9,
     THEORA
+#if defined(ENABLE_AC3_EAC3_AUDIO_DEMUXING)
+    ,
+    AC3,
+    EAC3
+#endif
   };
 
   bool GetMimeTypeFromExtension(const base::FilePath::StringType& ext,
@@ -491,6 +496,12 @@ 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:
+      return false;
+#endif
+
     case MimeUtil::VP9:
       // VP9 is supported only in KitKat+ (API Level 19).
       return base::android::BuildInfo::GetInstance()->sdk_int() >= 19;
@@ -541,6 +552,9 @@ 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,mp4a.a5,mp4a.a6,"

[ddorwin, 2015/02/26 20:49:32]

You only need one each for AC3 and EAC3.

[servolk, 2015/02/26 22:00:59]

Why? I believe these are just two different ways to indicate the same codec. For
example for EAC3, the ec-3 corresponds to the standard ETSI TS 102 366 v1.2.1,
while mp4a.a6 corresponds to the preferred way to specify codec according to RFC
6381. I think we should support both. I know for sure that, for example, Netflix
is using mp4a.a6, whereas I've seen other content providers using ec-3.

[ddorwin, 2015/02/26 22:06:18]

Because this doesn't do what you think it does. (That code is at line 606.) See
the comment in this area in tip of tree.

[servolk, 2015/02/26 22:29:20]

Could you elaborate? As far as I can see this adds those codecs to
format_codec_mappings for audio/mp4 and audio/x-m4a types, which leads to those
codecs being added to strict_format_map_ and consequently properly recognized in
IsSupportedStrictMediaMimeType, which is probably something that we want to do
in order to fully support those codecs on all code paths. Am I missing something
here?

[ddorwin, 2015/02/26 22:34:15]

Yes, but format_codec_mappings is converted to enums during initialization. See
https://codereview.chromium.org/952673002/diff/1/net/base/mime_util.cc#newcod...

[servolk, 2015/02/26 22:43:54]

Ah, ok, you are right, I missed the fact that they are converted into enums
instead of being registered as strings. So we should be good with adding just
one of the variants here, as long as we have all the variations in
format_codec_mappings. Working on it.

+#endif
     "mp4a.40.05,mp4a.40.29";
 static const char kMP4VideoCodecsExpression[] =
     "avc1.42E00A,avc1.4D400A,avc1.64000A,"
@@ -588,6 +602,12 @@ static const CodecIDMappings kUnambiguousCodecIDs[] = {
     {"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},

[ddorwin, 2015/02/26 20:49:32]

Please add browser tests.

[servolk, 2015/02/27 01:21:14]

Done.

+    {"ec-3", MimeUtil::EAC3},
+    {"mp4a.a5", MimeUtil::AC3},
+    {"mp4a.a6", MimeUtil::EAC3},
+#endif
     {"vorbis", MimeUtil::VORBIS},
     {"opus", MimeUtil::OPUS},
     {"vp8", MimeUtil::VP8},
@@ -887,6 +907,13 @@ 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.

[ddorwin, 2015/02/26 20:49:32]

Why is stripping okay? I don't think that is the intent of strip. Instead, you
should check whether the entire string is valid as we do for AVC levels.

[servolk, 2015/02/26 22:00:59]

Actually I'm not sure about that myself, that just a piece of code that we had
in downstream (Chromecast) code, that was added by somebody else, so I assumed
it was needed. I'll look into this some more.
Btw, note that this actually prevents the stripping.

+    // 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);
@@ -1059,6 +1086,10 @@ 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: