Fix wrong timing calculation for client/server clock drift. (#3759)

* Fix wrong timing calculation for client/server clock drift.

Author: dsilhavy

src/dash/utils/SegmentsUtils.js

@@ -164,8 +164,8 @@ function isSegmentAvailable(timelineConverter, representation, segment, isDynami
         // SAST = Period@start + seg@presentationStartTime + seg@duration
         // ASAST = SAST - ATO
         // SAET = SAST + TSBD + seg@duration
-
-        const refTime = timelineConverter.getAvailabilityWindowAnchorTime();
+        // refTime serves as an anchor time to compare the availability time of the segments against. Note that we already compensated for the client/server drift when calculating the availability time of a segment. Thats why we do not subtract clientServerTimeShift here again.
+        const refTime = Date.now() - ((timelineConverter.getTimelineAnchorAvailabilityOffset()) * 1000);
         return segment.availabilityStartTime.getTime() <= refTime && (!isFinite(segment.availabilityEndTime) || segment.availabilityEndTime.getTime() >= refTime);
     }
 

src/dash/utils/TimelineConverter.js

@@ -67,7 +67,7 @@ function TimelineConverter() {
         clientServerTimeShift = value;
     }
 
-    function calcAvailabilityTimeFromPresentationTime(presentationEndTime, representation, isDynamic, calculateAvailabilityEndTime) {
+    function _calcAvailabilityTimeFromPresentationTime(presentationEndTime, representation, isDynamic, calculateAvailabilityEndTime) {
         let availabilityTime;
         let mpd = representation.adaptation.period.mpd;
         const availabilityStartTime = mpd.availabilityStartTime;
@@ -99,15 +99,15 @@ function TimelineConverter() {
     }
 
     function calcAvailabilityStartTimeFromPresentationTime(presentationEndTime, representation, isDynamic) {
-        return calcAvailabilityTimeFromPresentationTime.call(this, presentationEndTime, representation, isDynamic);
+        return _calcAvailabilityTimeFromPresentationTime(presentationEndTime, representation, isDynamic);
     }
 
     function calcAvailabilityEndTimeFromPresentationTime(presentationEndTime, representation, isDynamic) {
-        return calcAvailabilityTimeFromPresentationTime.call(this, presentationEndTime, representation, isDynamic, true);
+        return _calcAvailabilityTimeFromPresentationTime(presentationEndTime, representation, isDynamic, true);
     }
 
     function calcPresentationTimeFromWallTime(wallTime, period) {
-        return ((wallTime.getTime() - period.mpd.availabilityStartTime.getTime() - clientServerTimeShift * 1000) / 1000);
+        return ((wallTime.getTime() - period.mpd.availabilityStartTime.getTime() + clientServerTimeShift * 1000) / 1000);
     }
 
     function calcPresentationTimeFromMediaTime(mediaTime, representation) {
@@ -138,10 +138,6 @@ function TimelineConverter() {
         return wallTime;
     }
 
-    function getAvailabilityWindowAnchorTime() {
-        return Date.now() - ((timelineAnchorAvailabilityOffset + clientServerTimeShift) * 1000);
-    }
-
     /**
      * Calculates the timeshiftbuffer range. This range might overlap multiple periods and is not limited to period boundaries. However, we make sure that the range is potentially covered by period.
      * @param {Array} streams
@@ -272,6 +268,10 @@ function TimelineConverter() {
         timelineAnchorAvailabilityOffset = now - range.end;
     }
 
+    function getTimelineAnchorAvailabilityOffset() {
+        return timelineAnchorAvailabilityOffset;
+    }
+
     function _adjustTimeBasedOnPeriodRanges(streams, time, isEndOfDvrWindow = false) {
         try {
             let i = 0;
@@ -360,7 +360,7 @@ function TimelineConverter() {
         initialize,
         getClientTimeOffset,
         setClientTimeOffset,
-        getAvailabilityWindowAnchorTime,
+        getTimelineAnchorAvailabilityOffset,
         calcAvailabilityStartTimeFromPresentationTime,
         calcAvailabilityEndTimeFromPresentationTime,
         calcPresentationTimeFromWallTime,