[backends] Fix image sqeuences with OpenCV 5.0

CAP_PROP_POS_MSEC returns -1 for image sequences with OpenCV 5.

Author: Breakthrough

scenedetect/backends/opencv.py

@@ -221,9 +221,10 @@ def timecode(self) -> Timecode:
     @property
     def position(self) -> FrameTimecode:
         timecode = self.timecode
-        # If PTS is 0 but we've read frames, derive from frame number.
-        # This handles image sequences and cases where CAP_PROP_POS_MSEC is unreliable.
-        if timecode.pts == 0 and self.frame_number > 0:
+        # If PTS is non-positive but we've read frames, derive from frame number. This handles
+        # image sequences and cases where CAP_PROP_POS_MSEC is unreliable. OpenCV 5 reports
+        # CAP_PROP_POS_MSEC as -1 (rather than 0) for image sequences on Windows, so check <= 0.
+        if timecode.pts <= 0 and self.frame_number > 0:
             fps = self.frame_rate
             time_base = Fraction(1, fps.numerator)
             pts = (self.frame_number - 1) * fps.denominator

website/pages/changelog.md

@@ -762,3 +762,4 @@ Development
  - [bugfix] The PyAV backend (`VideoStreamAv`) now skips corrupt frames during `read()` and continues decoding instead of failing, giving up only after 8 consecutive decode failures (matching the OpenCV backend's tolerance behavior)
  - [bugfix] The PyAV backend now normalizes presentation times by the stream start time, so files with a delayed start (e.g. from edit lists) report the first frame at `position` 0, consistent with other backends and with `seek()`
  - [bugfix] Comparisons between two `FrameTimecode` objects that both carry exact presentation times (e.g. positions from VFR videos) and share the same frame rate are now performed exactly using `pts` and `time_base` instead of rounded frame numbers. Previously, distinct frames in VFR sections could compare equal or fail strict ordering when their times rounded to the same approximate frame number. Comparisons involving frame- or seconds-based timecodes, plain values (`int`/`float`/`str`), or differing frame rates are unchanged
+ - [bugfix] Fix image sequence inputs when using OpenCV 5.0