count exact number of frames with ffprbe -count_frames

fiftyone/utils/video.py

@@ -6,6 +6,7 @@
 |
 """
 import itertools
+import json
 import logging
 import os
 
@@ -658,6 +659,33 @@ def concat_videos(input_paths, output_path, verbose=False):
             ffmpeg.run(input_list_path, output_path, verbose=verbose)
 
 
+def exact_frame_count(input_path):
+    """Returns the exact number of frames in the video.
+
+    This method uses -count_frames argument of ffprobe
+    which decodes the entire video to count the frames
+    and can be very slow.
+
+    Args:
+        input_path: the path to the video
+
+    Returns:
+        the number of frames in the video
+    """
+    opts = [
+        "-count_frames",
+        "-select_streams",
+        "v:0",
+        "-print_format",
+        "json",
+        "-show_streams",
+    ]
+    ffprobe = etav.FFprobe(opts=opts)
+    output = ffprobe.run(input_path)
+    output = json.loads(output.decode())
+    return int(output["streams"][0]["nb_read_frames"])
+
+
 def _transform_videos(
     sample_collection,
     frames=None,

tests/intensive/video_tests.py

@@ -15,6 +15,7 @@
 import fiftyone as fo
 import fiftyone.zoo as foz
 from fiftyone import ViewField as F
+import fiftyone.utils.video as fouv
 
 
 def test_to_clips():
@@ -458,6 +459,15 @@ def test_to_frame_eval_patches():
     print(patches.count_values("type"))
 
 
+def test_exact_frame_count():
+    dataset = foz.load_zoo_dataset("quickstart-video").clone()
+    dataset.limit(2).save()
+
+    for smp in dataset:
+        frame_count = fouv.exact_frame_count(smp.filepath)
+        assert frame_count == len(smp.frames)
+
+
 if __name__ == "__main__":
     fo.config.show_progress_bars = True
     unittest.main(verbosity=2)