monitor: Improve jump detection

Earlier, we used to simply calc the delta of file progress % between the
prev and cur states. If too much delta from last update, send scrobble.
But for small files (like, 2 minute duration), with a polling monitor
running every 10 seconds, we would hit this condition after each check.
Because, the progress delta in 10s is a significant chunk of the total
time. This would result in spurious "start" scrobbles every 10s.

Now we also estimate the "expected" progress between the two states,
based on their "updated_at" times as a % of total duration. Now, if
this "expected" progress is too far from the measured progress, we send
the scrobble. This assumes that the file is being played at 1x speed.

Author: iamkroot

trakt_scrobbler/player_monitors/monitor.py

@@ -57,6 +57,31 @@ def progress(self) -> float:
     def abs_progress(self) -> float:
         return abs(self.progress)
 
+    @property
+    def expected_progress_delta(self) -> float:
+        """Calculate expected % of file played between the two states.
+        Example: duration=50seconds, prev.upd_at=5, cur.upd_at=12
+        Here, elapsed time=7s; we expect (12-5)/50=7/50=14% of progress delta
+        """
+        if self.prev['duration'] != self.current['duration'] or self.current['state'] != State.Playing:
+            # doesn't make sense to have an expected progress in these cases.
+            return 0
+        return 100 * self.elapsed_realtime / self.current['duration']
+
+    @property
+    def progress_skipped(self) -> float:
+        """Compare the progress with the expected progress based on real time.
+        
+        Continuing above example, if prev.prog=8%, and expected_prog_delta=14%, 
+        cur.prog _should be_ 8+14 = 22%.
+        We calculate ((cur.prog - prev.prog) - exp_delta), should be close to 0.
+        """
+        return self.progress - self.expected_progress_delta
+
+    @property
+    def abs_progress_skipped(self) -> float:
+        return abs(self.progress_skipped)
+
 
 class Monitor(Thread):
     """Generic base class that polls the player for state changes,
@@ -185,6 +210,7 @@ def parse_status(status):
         progress = min(round(status['position'] * 100 / status['duration'], 2), 100)
         return {
             'state': status['state'],
+            'duration': status['duration'],
             'progress': progress,
             'media_info': media_info,
             'updated_at': time.time(),
@@ -218,10 +244,10 @@ def decide_action(self, prev, current):
                     not prev 
                     or not transition.is_same_media
                     or transition.state_changed
-                    or transition.abs_progress > self.skip_interval
+                    or transition.abs_progress_skipped > self.skip_interval
                 ):
                     yield 'scrobble'
-        elif transition.state_changed or transition.abs_progress > self.skip_interval:
+        elif transition.state_changed or transition.abs_progress_skipped > self.skip_interval:
             # state changed
             if self.preview:
                 if current['state'] == State.Stopped:
@@ -235,7 +261,7 @@ def decide_action(self, prev, current):
             elif self.fast_pause:
                 if (
                     current['state'] == State.Stopped
-                    or transition.abs_progress > self.skip_interval
+                    or transition.abs_progress_skipped > self.skip_interval
                 ):
                     yield 'scrobble'
                     yield 'exit_fast_pause'