UpdateCurrentDelay should update delay with rounding errors

Some of the timestamps input into UpdateCurrentDelay are not truncated
to milliseconds and thus a small negative delay can result. This means
the delay will not update when it should have.

Bug: webrtc:14168
Change-Id: I5293339b6a39201c680854e9596b717025ee8dc1
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/266370
Reviewed-by: Erik Språng <sprang@webrtc.org>
Commit-Queue: Evan Shrubsole <eshr@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#37657}

modules/video_coding/timing/timing.cc

@@ -157,7 +157,9 @@ void VCMTiming::UpdateCurrentDelay(Timestamp render_time,
   TimeDelta target_delay = TargetDelayInternal();
   TimeDelta delayed =
       (actual_decode_time - render_time) + RequiredDecodeTime() + render_delay_;
-  if (delayed < TimeDelta::Zero()) {
+
+  // Only consider `delayed` as negative by more than a few microseconds.
+  if (delayed.ms() < 0) {
     return;
   }
   if (current_delay_ + delayed <= target_delay) {

modules/video_coding/timing/timing_unittest.cc

@@ -316,4 +316,24 @@ TEST(ReceiverTimingTest, MaxWaitingTimeReturnsZeroIfTooManyFramesQueuedIsTrue) {
             TimeDelta::Zero());
 }
 
+TEST(ReceiverTimingTest, UpdateCurrentDelayCapsWhenOffByMicroseconds) {
+  test::ScopedKeyValueConfig field_trials;
+  SimulatedClock clock(0);
+  VCMTiming timing(&clock, field_trials);
+  timing.Reset();
+
+  // Set larger initial current delay.
+  timing.set_min_playout_delay(TimeDelta::Millis(200));
+  timing.UpdateCurrentDelay(Timestamp::Millis(900), Timestamp::Millis(1000));
+
+  // Add a few microseconds to ensure that the delta of decode time is 0 after
+  // rounding, and should reset to the target delay.
+  timing.set_min_playout_delay(TimeDelta::Millis(50));
+  Timestamp decode_time = Timestamp::Millis(1337);
+  Timestamp render_time =
+      decode_time + TimeDelta::Millis(10) + TimeDelta::Micros(37);
+  timing.UpdateCurrentDelay(render_time, decode_time);
+  EXPECT_EQ(timing.GetTimings().current_delay, timing.TargetVideoDelay());
+}
+
 }  // namespace webrtc