Adds support for mp4a.40.34 mp3 in HLS

When including mp3 files in an HLS stream, the officially supported
codec is mp4a.40.34, according to the HLS FAQ (https://goo.gl/11ZdLh).
This codec string, unfortunately, is not recognized by MSE
implementations on platforms other than Safari.
Therefore, this change omits that codec string.

This change also modifies the start time code in the parser to assume
that mp3 files have a start time of 0.

Closes #1210

Change-Id: I5ccad3f8713fdcafecceff923a4d16ce8fb3ace3

lib/hls/hls_parser.js

@@ -447,6 +447,14 @@ shaka.hls.HlsParser.prototype.createVariantsForTag_ = function(tag, playlist) {
     height = resBlocks[1];
   }
 
+  codecs = codecs.filter(function(codec) {
+    // mp4a.40.34 is a nonstandard codec string that is sometimes used in HLS
+    // for legacy reasons. It is not recognized by non-Apple MSE.
+    // See https://bugs.chromium.org/p/chromium/issues/detail?id=489520
+    // Therefore, ignore this codec string.
+    return codec != 'mp4a.40.34';
+  });
+
   // After filtering, this is a list of the media tags we will process to
   // combine with the variant tag (EXT-X-STREAM-INF) we are working on.
   var mediaTags = Utils.filterTagsByName(playlist.tags, 'EXT-X-MEDIA');
@@ -1293,6 +1301,10 @@ shaka.hls.HlsParser.prototype.getStartTime_ =
   return this.fetchPartialSegment_(segmentRef).then(function(response) {
     if (mimeType == 'video/mp4' || mimeType == 'audio/mp4') {
       return this.getStartTimeFromMp4Segment_(response.data);
+    } else if (mimeType == 'audio/mpeg') {
+      // There is no standard way to embed a timestamp in an mp3 file, so the
+      // start time is presumably 0.
+      return 0;
     } else if (mimeType == 'video/mp2t') {
       return this.getStartTimeFromTsSegment_(response.data);
     } else if (mimeType == 'application/mp4' ||