Fix variant switching media index test

The original test was invoking the playlist reload callback which tested whether the media index was updating correctly after a refresh. Now, the test correctly triggers the a variant switch after downloading a segment. Consolidated media index update code and ensured state is properly updated after a switch.

src/videojs-hls.js

@@ -122,6 +122,42 @@ var
 
   },
 
+  /**
+   * Determine the media index in one playlist that corresponds to a
+   * specified media index in another. This function can be used to
+   * calculate a new segment position when a playlist is reloaded or a
+   * variant playlist is becoming active.
+   * @param mediaIndex {number} the index into the original playlist
+   * to translate
+   * @param original {object} the playlist to translate the media
+   * index from
+   * @param update {object} the playlist to translate the media index
+   * to
+   * @param {number} the corresponding media index in the updated
+   * playlist
+   */
+  findCorrespondingMediaIndex = function(mediaIndex, original, update) {
+    var
+      i = update.segments.length,
+      originalSegment;
+
+    // no segments have been loaded from the original playlist
+    if (mediaIndex === 0) {
+      return 0;
+    }
+
+    // try to sync based on URI
+    originalSegment = original.segments[mediaIndex - 1];
+    while (i--) {
+      if (originalSegment.uri === update.segments[i].uri) {
+        return i + 1;
+      }
+    }
+
+    // sync on media sequence
+    return (original.mediaSequence + mediaIndex) - update.mediaSequence;
+  },
+
   /**
    * Calculate the total duration for a playlist based on segment metadata.
    * @param playlist {object} a media playlist object
@@ -316,6 +352,10 @@ var
           mediaSequence > (playlist.mediaSequence || 0) + playlist.segments.length) {
         downloadPlaylist(resolveUrl(srcUrl, playlist.uri));
       } else {
+        player.hls.mediaIndex =
+          findCorrespondingMediaIndex(player.hls.mediaIndex,
+                                      player.hls.media,
+                                      playlist);
         player.hls.media = playlist;
 
         // update the duration
@@ -411,27 +451,7 @@ var
       var xhr = new window.XMLHttpRequest();
       xhr.open('GET', url);
       xhr.onreadystatechange = function() {
-        var i, parser, playlist, playlistUri, refreshDelay,
-          updateMediaIndex = function(original, update) {
-            var
-              i = update.segments.length,
-              updatedIndex = 0,
-              originalSegment;
-
-            // no segments have been loaded from the original playlist
-            if (player.hls.mediaIndex === 0) {
-              return;
-            }
-
-            originalSegment = original.segments[player.hls.mediaIndex - 1];
-            while (i--) {
-              if (originalSegment.uri === update.segments[i].uri) {
-                updatedIndex = i + 1;
-                break;
-              }
-            }
-            player.hls.mediaIndex = updatedIndex;
-          };
+        var i, parser, playlist, playlistUri, refreshDelay;
 
         // wait until the request completes
         if (xhr.readyState !== 4) {
@@ -487,7 +507,11 @@ var
 
               // determine the new mediaIndex if we're updating the
               // current media playlist
-              updateMediaIndex(playlist, parser.manifest);
+              player.hls.mediaIndex =
+                findCorrespondingMediaIndex(player.hls.mediaIndex,
+                                            playlist,
+                                            parser.manifest);
+              player.hls.media = parser.manifest;
             }
           }
         } else {

test/videojs-hls_test.js

@@ -991,7 +991,7 @@ test('updates the media index when a playlist reloads', function() {
     '3.ts\n';
   callback();
 
-  strictEqual(2, player.hls.mediaIndex, 'mediaIndex is updated after the reload');
+  strictEqual(player.hls.mediaIndex, 2, 'mediaIndex is updated after the reload');
 });
 
 test('mediaIndex is zero before the first segment loads', function() {
@@ -1012,42 +1012,39 @@ test('mediaIndex is zero before the first segment loads', function() {
 });
 
 test('reloads out-of-date live playlists when switching variants', function() {
-  var callback;
-  // capture timeouts
-  window.setTimeout = function(cb) {
-    callback = cb;
-  };
-
   player.hls('http://example.com/master.m3u8');
   videojs.mediaSources[player.currentSrc()].trigger({
     type: 'sourceopen'
   });
 
-  // playing segment 15 on playlist 0
   player.hls.master = {
     playlists: [{
       mediaSequence: 15,
-      segments: [{}, {}]
+      segments: [1, 1, 1]
     }, {
       uri: 'http://example.com/variant-update.m3u8',
       mediaSequence: 0,
-      segments: [{}, {}]
+      segments: [1, 1]
     }]
   };
+  // playing segment 15 on playlist zero
   player.hls.media = player.hls.master.playlists[0];
-  player.mediaIndex = 0;
+  player.mediaIndex = 1;
   window.manifests['variant-update'] = '#EXTM3U\n' +
     '#EXT-X-MEDIA-SEQUENCE:16\n' +
     '#EXTINF:10,\n' +
-    '16.ts\n';
+    '16.ts\n' +
+    '#EXTINF:10,\n' +
+    '17.ts\n';
 
   // switch playlists
   player.hls.selectPlaylist = function() {
     return player.hls.master.playlists[1];
   };
+  // timeupdate downloads segment 16 then switches playlists
   player.trigger('timeupdate');
 
-  ok(callback, 'reload is scheduled');
+  strictEqual(player.mediaIndex, 1, 'mediaIndex points at the next segment');
 });
 
 })(window, window.videojs);