MSE: Record counts of detected MSE audio, video and text tracks

media/formats/mp4/box_definitions.cc

Index: media/formats/mp4/box_definitions.cc
diff --git a/media/formats/mp4/box_definitions.cc b/media/formats/mp4/box_definitions.cc
index a95c78f9d163da7dbd052c74b3690b25cb46e7a3..f425fa9f8c6a0f163bf7150184f48fc87241b721 100644
--- a/media/formats/mp4/box_definitions.cc
+++ b/media/formats/mp4/box_definitions.cc
@@ -461,6 +461,9 @@ bool HandlerReference::Parse(BoxReader* reader) {
     type = kVideo;
   } else if (hdlr_type == FOURCC_SOUN) {
     type = kAudio;
+  } else if (hdlr_type == FOURCC_META || hdlr_type == FOURCC_SUBT ||

[wolenetz, 2016/03/23 01:45:50]

Note, this follows the logic in
https://dev.w3.org/html5/html-sourcing-inband-tracks/#mpeg4
Note also that 608/708 caption data inside a video track is not yet detected
(see also new https://crbug.com/597073 and new MSE spec bug
https://github.com/w3c/media-source/issues/58). tl;dr: we don't have enough
information in just an initialization segment to detect that caption data.
Discussion is ongoing in the spec bug to see how the spec might need to change
to support 608 / 708 caption data population into SourceBuffer.textTracks and
HTMLMediaElement.textTrcks.

[chcunningham, 2016/03/23 23:05:56]

Acknowledged.

+             hdlr_type == FOURCC_TEXT) {
+    type = kText;
   } else {
     type = kInvalid;
   }