minor code fixes for better input and error handling

Co-authored-by: Leonid Kostrykin <void@evoid.de>

Author: rmassei

tools/cv2/cv2_extract_frames.py

@@ -37,9 +37,14 @@ def extract_frames(output_dir: Union[str, Path], video_path: Union[str, Path], s
         frame_count = video.get(cv2.CAP_PROP_FRAME_COUNT)
         print('Total frames:', frame_count)
 
-        start_frame = int(start_time * fps)
-        end_frame = int(end_time * fps)
-        print(f'Starting extracting from frame {start_frame} until {end_frame}...')
+        start_frame = round(start_time * fps)
+        end_frame = round(end_time * fps)
+        if end_frame >= frame_count:
+            exit("End frame is beyond the end of the sequence.")
+        end_frame %= frame_count
+        if start_frame > end_frame:
+            exit("Start frame is beyond the end frame.")
+        print(f'Starting extracting from frame {start_frame} until {end_frame}...')
 
         video.set(cv2.CAP_PROP_POS_FRAMES, start_frame)
         current_frame = start_frame
@@ -62,7 +67,7 @@ def extract_frames(output_dir: Union[str, Path], video_path: Union[str, Path], s
         print('Extraction was successfully executed. Enjoy your frames.')
 
     except IOError:
-        print("Cannot open video file")
+        exit("Cannot open video file.")
 
 
 if __name__ == "__main__":

tools/cv2/cv2_extract_frames.xml

@@ -36,7 +36,7 @@
     </command>
     <inputs>
         <param name="video_path" type="data" optional="False" format="mp4,avi" label="Input video to convert"/>
-        <param name="start_time" type="float" value= "0" optional="False" label="Start time (seconds)" help="Start time in seconds"/>
+        <param name="start_time" type="float" value= "0" min="0" optional="False" label="Start time (seconds)" help="Start time in seconds"/>
         <param name="end_time" type="float" value= "-1" optional="False" label="End time (seconds)" help="End time in seconds"/>
         <param name="convert_to_grey" type="boolean" label="Convert output to single-channel grayscale?" help="Convert the file to grayscale (will be RGB otherwise)."/>
     </inputs>