Handle duration a little more intelligently

- If the playlist hasn't been loaded yet, use 0.
- If the playlist duration is Infinity, use the playlist duration.
- If the mediaSource doesn't exist, use the playlist duration.
- In all other cases, use the mediaSource's duration.

@@ -506,11 +506,23 @@ videojs.HlsHandler.prototype.setCurrentTime = function(currentTime) {
 };
 
 videojs.HlsHandler.prototype.duration = function() {
-  var playlists = this.playlists;
+  var
+    playlists = this.playlists,
+    playlistDuration;
+
   if (playlists) {
-    return videojs.Hls.Playlist.duration(playlists.media());
+    playlistDuration = videojs.Hls.Playlist.duration(playlists.media());
+  } else {
+    return 0;
+  }
+
+  if (playlistDuration === Infinity) {
+    return playlistDuration;
+  } else if (this.mediaSource) {
+    return this.mediaSource.duration;
+  } else {
+    return playlistDuration;
   }
-  return 0;
 };
 
 videojs.HlsHandler.prototype.seekable = function() {