fix(HLS): Fix interpretation of DEFAULT and AUTOSELECT

Previously, we treated the mere presense of either the DEFAULT or
AUTOSELECT attributes as an indication of a primary language.
However, AUTOSELECT should not be used in this way at all, and both
attributes can have a value of NO, so mere presence or absence is not
enough.

Instead, we must check for DEFAULT=YES to indicate a primary language.

Fixes shaka-project#2880

Change-Id: Ie107f079c06beb89ee5a6a51375af7a72fdd9021

lib/hls/hls_parser.js

@@ -1108,9 +1108,16 @@ shaka.hls.HlsParser = class {
 
     const language = this.getLanguage_(tag);
     const name = tag.getAttributeValue('NAME');
-    const defaultAttr = tag.getAttribute('DEFAULT');
-    const autoselectAttr = tag.getAttribute('AUTOSELECT');
-    const primary = !!defaultAttr || !!autoselectAttr;
+
+    // NOTE: According to the HLS spec, "DEFAULT=YES" requires "AUTOSELECT=YES".
+    // However, we don't bother to validate "AUTOSELECT", since we don't
+    // actually use it in our streaming model, and we treat everything as
+    // "AUTOSELECT=YES".  A value of "AUTOSELECT=NO" would imply that it may
+    // only be selected explicitly by the user, and we don't have a way to
+    // represent that in our model.
+    const defaultAttrValue = tag.getAttribute('DEFAULT');
+    const primary = defaultAttrValue == 'YES';
+
     const channelsCount = type == 'audio' ? this.getChannelsCount_(tag) : null;
     const characteristics = tag.getAttributeValue('CHARACTERISTICS');
     // TODO: Should we take into account some of the currently ignored