[Fix] Fix#306

mmaction/datasets/pipelines/loading.py

@@ -417,28 +417,11 @@ def __init__(self, clip_len, frame_interval=2, test_mode=False):
         super().__init__(clip_len, frame_interval, test_mode=test_mode)
 
     def _get_clips(self, center_index, skip_offsets, shot_info):
-        frame_inds = list()
-        ori_clip_len = self.clip_len * self.frame_interval
-
-        cur = center_index - self.frame_interval
-        length = len(
-            range(-self.frame_interval,
-                  -(ori_clip_len + 1) // self.frame_interval,
-                  -self.frame_interval))
-
-        for i in range(length):
-            frame_inds.append(cur + skip_offsets[i])
-            if cur - self.frame_interval >= shot_info[0]:
-                cur -= self.frame_interval
-
-        cur = center_index
-        length = len(
-            range(0, (ori_clip_len + 1) // self.frame_interval,
-                  self.frame_interval))
-        for i in range(length):
-            frame_inds.append(cur + skip_offsets[i])
-            if cur + self.frame_interval < shot_info[1]:
-                cur += self.frame_interval
+        start = center_index - (self.clip_len // 2) * self.frame_interval
+        end = center_index + ((self.clip_len + 1) // 2) * self.frame_interval
+        frame_inds = list(range(start, end, self.frame_interval))
+        frame_inds = frame_inds + skip_offsets
+        frame_inds = np.clip(frame_inds, shot_info[0], shot_info[1] - 1)
 
         return frame_inds
 
@@ -449,8 +432,10 @@ def __call__(self, results):
         shot_info = results['shot_info']
 
         center_index = fps * (timestamp - timestamp_start) + 1
+
         skip_offsets = np.random.randint(
-            self.frame_interval, size=self.clip_len)
+            -self.frame_interval // 2, (self.frame_interval + 1) // 2,
+            size=self.clip_len)
         frame_inds = self._get_clips(center_index, skip_offsets, shot_info)
 
         results['frame_inds'] = np.array(frame_inds, dtype=np.int)

tests/test_data/test_loading.py

@@ -642,6 +642,15 @@ def test_sample_ava_frames(self):
         assert ava_result['frame_interval'] == 2
         assert len(ava_result['frame_inds']) == 32
 
+        # add test case in Issue #306
+        config = dict(clip_len=8, frame_interval=8)
+        sample_ava_dataset = SampleAVAFrames(**config)
+        ava_result = sample_ava_dataset(results=self.ava_results)
+        assert self.check_keys_contain(ava_result.keys(), target_keys)
+        assert ava_result['clip_len'] == 8
+        assert ava_result['frame_interval'] == 8
+        assert len(ava_result['frame_inds']) == 8
+
     def test_sample_proposal_frames(self):
         target_keys = [
             'frame_inds', 'clip_len', 'frame_interval', 'num_clips',