Increase HLS partial segment size

This increases the amount of data we fetch to get HLS segment start
times.  The presence of a large PSSH box in Widevine-encrypted content
was pushing the "tfdt" box past the 1kB mark, so we will now fetch
2kB.

Issue #1137
References FR in shaka-project/shaka-packager#294

Change-Id: I51a1407c4d992e42d07c3e6c6c501051100d1620

lib/hls/hls_parser.js

@@ -1298,6 +1298,12 @@ shaka.hls.HlsParser.prototype.getStartTime_ =
     shaka.log.debug('Unable to find segment start time in previous manifest!');
   }
 
+  // TODO: Introduce a new tag to extend HLS and provide the first segment's
+  // start time.  This will avoid the need for these fetches in content packaged
+  // with Shaka Packager.  This web-friendly extension to HLS can then be
+  // proposed to Apple for inclusion in a future version of HLS.
+  // See https://github.com/google/shaka-packager/issues/294
+
   shaka.log.v1('Fetching segment to find start time');
   return this.fetchPartialSegment_(segmentRef).then(function(response) {
     if (mimeType == 'video/mp4' || mimeType == 'audio/mp4') {
@@ -1977,7 +1983,7 @@ shaka.hls.HlsParser.TS_TIMESCALE_ = 90000;
  * @const {number}
  * @private
  */
-shaka.hls.HlsParser.PARTIAL_SEGMENT_SIZE_ = 1024;
+shaka.hls.HlsParser.PARTIAL_SEGMENT_SIZE_ = 2048;
 
 
 shaka.media.ManifestParser.registerParserByExtension(

test/hls/hls_live_unit.js

@@ -516,7 +516,7 @@ describe('HlsParser live', function() {
 
       it('gets start time of segments with byte range', function(done) {
         // Nit: this value is an implementation detail of the fix for #1106
-        var partialEndByte = expectedStartByte + 1024 - 1;
+        var partialEndByte = expectedStartByte + 2048 - 1;
 
         fakeNetEngine.setResponseMap({
           'test:/master': toUTF8(master),

test/hls/hls_parser_unit.js

@@ -1306,7 +1306,7 @@ describe('HlsParser', function() {
     var expectedStartByte = 616;
     var expectedEndByte = 121705;
     // Nit: this value is an implementation detail of the fix for #1106
-    var partialEndByte = expectedStartByte + 1024 - 1;
+    var partialEndByte = expectedStartByte + 2048 - 1;
 
     beforeEach(function() {
       // TODO: use StreamGenerator?