Clean up outdated references to "period-relative"

Segment times and positions are no longer period-relative.

Issue #1339

Change-Id: If2b1b7d56ac49d50439598403f681a2da88ce605

lib/media/segment_reference.js

@@ -81,17 +81,16 @@ shaka.media.InitSegmentReference = class {
  */
 shaka.media.SegmentReference = class {
   /**
-   * @param {number} position The segment's position within a particular Period.
-   *   The following should hold true between any two SegmentReferences from the
-   *   same Period, r1 and r2:
+   * @param {number} position The segment's position.
+   *   The following should hold true between any two SegmentReferences r1 and
+   *   r2:
    *   IF r2.position > r1.position THEN
    *     [ (r2.startTime > r1.startTime) OR
    *       (r2.startTime == r1.startTime AND r2.endTime >= r1.endTime) ]
-   * @param {number} startTime The segment's start time in seconds, relative to
-   *   the start of a particular Period.
-   * @param {number} endTime The segment's end time in seconds, relative to
-   *   the start of a particular Period.  The segment ends the instant before
-   *   this time, so |endTime| must be strictly greater than |startTime|.
+   * @param {number} startTime The segment's start time in seconds.
+   * @param {number} endTime The segment's end time in seconds.  The segment
+   *   ends the instant before this time, so |endTime| must be strictly greater
+   *   than |startTime|.
    * @param {function():!Array.<string>} uris
    *   A function that creates the URIs of the resource containing the segment.
    * @param {number} startByte The offset from the start of the resource to the
@@ -104,12 +103,16 @@ shaka.media.SegmentReference = class {
    *   are self-initializing.
    * @param {number} timestampOffset
    *   The amount of time, in seconds, that must be added to the segment's
-   *   internal timestamps to align it to the presentation timeline.  This
-   *   value should equal the Period start time minus the first presentation
-   *   timestamp of the first frame/sample in the Period.  For example, for MP4
-   *   based streams, this value should equal Period start minus the first
-   *   segment's tfdt box's 'baseMediaDecodeTime' field (after it has been
-   *   converted to seconds).
+   *   internal timestamps to align it to the presentation timeline.
+   *   <br>
+   *   For DASH, this value should equal the Period start time minus the first
+   *   presentation timestamp of the first frame/sample in the Period.  For
+   *   example, for MP4 based streams, this value should equal Period start
+   *   minus the first segment's tfdt box's 'baseMediaDecodeTime' field (after
+   *   it has been converted to seconds).
+   *   <br>
+   *   For HLS, this value should be 0 to keep the presentation time at the most
+   *   recent discontinuity minus the corresponding media time.
    * @param {number} appendWindowStart
    *   The start of the append window for this reference, relative to the
    *   presentation.  Any content from before this time will be removed by
@@ -160,7 +163,7 @@ shaka.media.SegmentReference = class {
   }
 
   /**
-   * Returns the segment's position within a particular Period.
+   * Returns the segment's position.
    *
    * @return {number} The segment's position.
    * @export
@@ -170,8 +173,7 @@ shaka.media.SegmentReference = class {
   }
 
   /**
-   * Returns the segment's start time in seconds, relative to
-   * the start of a particular Period.
+   * Returns the segment's start time in seconds.
    *
    * @return {number}
    * @export
@@ -181,8 +183,7 @@ shaka.media.SegmentReference = class {
   }
 
   /**
-   * Returns the segment's end time in seconds, relative to
-   * the start of a particular Period.
+   * Returns the segment's end time in seconds.
    *
    * @return {number}
    * @export