Calculate preciseDuration correctly around discontinuities

Don't use previous segment timestamps to calculate the precise duration of a segment so that we don't have to worry about timestamp discontinuities. Update to contrib-media-sources 1.0.

@@ -44,7 +44,7 @@
   },
   "dependencies": {
     "pkcs7": "^0.2.2",
-    "videojs-contrib-media-sources": "^0.3.0",
+    "videojs-contrib-media-sources": "^1.0.0",
     "videojs-swf": "^4.6.0"
   }
 }

+/**
+ * An object that stores the bytes of an FLV tag and methods for
+ * querying and manipulating that data.
+ * @see http://download.macromedia.com/f4v/video_file_format_spec_v10_1.pdf
+ */
 (function(window) {
 
 window.videojs = window.videojs || {};
@@ -358,4 +363,26 @@ hls.FlvTag.frameTime = function(tag) {
   return pts;
 };
 
+/**
+ * Calculate the media timeline duration represented by an array of
+ * tags. This function assumes the tags are already pre-sorted by
+ * presentation timestamp (PTS), in ascending order. Returns zero if
+ * there are less than two FLV tags to inspect.
+ * @param tags {array} the FlvTag objects to query
+ * @return the number of milliseconds between the display time of the
+ * first tag and the last tag.
+ */
+hls.FlvTag.durationFromTags = function(tags) {
+  if (tags.length < 2) {
+    return 0;
+  }
+
+  var first = tags[0], last = tags[tags.length - 1], frameDuration;
+
+  // use the interval between the last two tags or assume 24 fps
+  frameDuration = last.pts - tags[tags.length - 2].pts || (1/24);
+
+  return (last.pts - first.pts) + frameDuration;
+};
+
 })(this);

@@ -714,7 +714,6 @@ videojs.Hls.prototype.drainBuffer = function(event) {
     tags,
     bytes,
     segment,
-    durationOffset,
     decrypter,
     segIv,
     ptsTime,
@@ -788,23 +787,11 @@ videojs.Hls.prototype.drainBuffer = function(event) {
     tags.push(this.segmentParser_.getNextTag());
   }
 
-  // This block of code uses the presentation timestamp of the ts segment to calculate its exact duration, since this
-  // may differ by fractions of a second from what is reported. Using the exact, calculated 'preciseDuration' allows
-  // for smoother seeking and calculation of the total playlist duration, which previously (especially in short videos)
-  // was reported erroneously and made the play head overrun the end of the progress bar.
+  // Use the presentation timestamp of the ts segment to calculate its
+  // exact duration, since this may differ by fractions of a second
+  // from what is reported in the playlist
   if (tags.length > 0) {
-    segment.preciseTimestamp = tags[tags.length - 1].pts;
-
-    if (playlist.segments[mediaIndex - 1]) {
-      if (playlist.segments[mediaIndex - 1].preciseTimestamp) {
-        durationOffset = playlist.segments[mediaIndex - 1].preciseTimestamp;
-      } else {
-        durationOffset = (playlist.targetDuration * (mediaIndex - 1) + playlist.segments[mediaIndex - 1].duration) * 1000;
-      }
-      segment.preciseDuration = (segment.preciseTimestamp - durationOffset) / 1000;
-    } else if (mediaIndex === 0) {
-      segment.preciseDuration = segment.preciseTimestamp / 1000;
-    }
+    segment.preciseDuration = videojs.Hls.FlvTag.durationFromTags(tags) * 0.001;
   }
 
   this.updateDuration(this.playlists.media());

@@ -57,4 +57,32 @@ test('writeBytes grows the internal byte array dynamically', function() {
   }
 });
 
+test('calculates the duration of a tag array from PTS values', function() {
+  var tags = [], count = 20, i;
+
+  for (i = 0; i < count; i++) {
+    tags[i] = new FlvTag(FlvTag.VIDEO_TAG);
+    tags[i].pts = i * 1000;
+  }
+
+  equal(FlvTag.durationFromTags(tags), count * 1000, 'calculated duration from PTS values');
+});
+
+test('durationFromTags() assumes 24fps if the last frame duration cannot be calculated', function() {
+  var tags = [
+    new FlvTag(FlvTag.VIDEO_TAG),
+    new FlvTag(FlvTag.VIDEO_TAG),
+    new FlvTag(FlvTag.VIDEO_TAG)
+  ];
+  tags[0].pts = 0;
+  tags[1].pts = tags[2].pts = 1000;
+
+  equal(FlvTag.durationFromTags(tags), 1000 + (1/24) , 'assumes 24fps video');
+});
+
+test('durationFromTags() returns zero if there are less than two frames', function() {
+  equal(FlvTag.durationFromTags([]), 0, 'returns zero for empty input');
+  equal(FlvTag.durationFromTags([new FlvTag(FlvTag.VIDEO_TAG)]), 0, 'returns zero for a singleton input');
+});
+
 })(this);

@@ -1086,8 +1086,11 @@ test('flushes the parser after each segment', function() {
   strictEqual(flushes, 1, 'tags are flushed at the end of a segment');
 });
 
-test('calculates preciseTimestamp and preciseDuration for a new segment', function() {
-  var tags = [{ pts : 200000, bytes: new Uint8Array(1) }];
+test('calculates preciseDuration for a new segment', function() {
+  var tags = [
+    { pts : 200 * 1000, bytes: new Uint8Array(1) },
+    { pts : 300 * 1000, bytes: new Uint8Array(1) }
+  ];
   videojs.Hls.SegmentParser = mockSegmentParser(tags);
 
   player.src({
@@ -1099,11 +1102,40 @@ test('calculates preciseTimestamp and preciseDuration for a new segment', functi
   standardXHRResponse(requests[0]);
   strictEqual(player.duration(), 40, 'player duration is read from playlist on load');
   standardXHRResponse(requests[1]);
-  strictEqual(player.hls.playlists.media().segments[0].preciseTimestamp, 200000, 'preciseTimestamp is calculated and stored');
   strictEqual(player.hls.playlists.media().segments[0].preciseDuration, 200, 'preciseDuration is calculated and stored');
   strictEqual(player.duration(), 230, 'player duration is calculated using preciseDuration');
 });
 
+test('calculates preciseDuration correctly around discontinuities', function() {
+  var tags = [];
+  videojs.Hls.SegmentParser = mockSegmentParser(tags);
+  player.src({
+    src: 'manifest/media.m3u8',
+    type: 'application/vnd.apple.mpegurl'
+  });
+  openMediaSource(player);
+  requests.shift().respond(200, null,
+                           '#EXTM3U\n' +
+                           '#EXTINF:10,\n' +
+                           '0.ts\n' +
+                           '#EXT-X-DISCONTINUITY\n' +
+                           '#EXTINF:10,\n' +
+                           '1.ts\n' +
+                           '#EXT-X-ENDLIST\n');
+  tags.push({ pts: 10 * 1000, bytes: new Uint8Array(1) });
+  standardXHRResponse(requests.shift()); // segment 0
+  player.hls.checkBuffer_();
+
+  // the PTS value of the second segment is *earlier* than the first
+  tags.push({ pts: 0 * 1000, bytes: new Uint8Array(1) });
+  tags.push({ pts: 5 * 1000, bytes: new Uint8Array(1) });
+  standardXHRResponse(requests.shift()); // segment 1
+
+  equal(player.hls.playlists.media().segments[1].preciseDuration,
+        5 + 5, // duration includes the time to display the second tag
+        'duration is independent of previous segments');
+});
+
 test('exposes in-band metadata events as cues', function() {
   var track;
   player.src({