add reversing videos tutorial

Author: x4nth055

Diff for: README.md

@@ -173,6 +173,7 @@ This is a repository of all the tutorials of [The Python Code](https://www.thepy
     - [How to Concatenate Video Files in Python](https://www.thepythoncode.com/article/concatenate-video-files-in-python). ([code](python-for-multimedia/combine-video))
     - [How to Concatenate Audio Files in Python](https://www.thepythoncode.com/article/concatenate-audio-files-in-python). ([code](python-for-multimedia/combine-audio))
     - [How to Extract Frames from Video in Python](https://www.thepythoncode.com/article/extract-frames-from-videos-in-python). ([code](python-for-multimedia/extract-frames-from-video))
+    - [How to Reverse Videos in Python](https://www.thepythoncode.com/article/reverse-video-in-python). ([code](python-for-multimedia/reverse-video))
 
 
 For any feedback, please consider pulling requests.

Diff for: python-for-multimedia/reverse-video/README.md

@@ -0,0 +1,7 @@
+# [How to Reverse Videos in Python](https://www.thepythoncode.com/article/reverse-video-in-python)
+To run this:
+- `pip3 install -r requirements.txt`
+- 
+    ```
+    $ python reverse_video.py Tenet-the-breach-scene-in-forward.mp4
+    ```

Diff for: python-for-multimedia/reverse-video/Tenet-the-breach-scene-in-forward.mp4

@@ -0,0 +1,3 @@
+tqdm
+moviepy
+numpy

Diff for: python-for-multimedia/reverse-video/requirements.txt

@@ -0,0 +1,76 @@
+from moviepy.editor import VideoFileClip, ImageSequenceClip
+import numpy as np
+import os
+from datetime import timedelta, datetime
+from glob import glob
+from tqdm import tqdm
+import shutil
+
+# i.e if video of duration 30 seconds, saves 10 frame per second = 300 frames saved in total
+SAVING_FRAMES_PER_SECOND = 30
+
+def format_timedelta(td):
+    """Utility function to format timedelta objects in a cool way (e.g 00:00:20.05) 
+    omitting microseconds and retaining milliseconds"""
+    result = str(td)
+    try:
+        result, ms = result.split(".")
+    except ValueError:
+        return result + ".00".replace(":", "-")
+    ms = int(ms)
+    ms = round(ms / 1e4)
+    return f"{result}.{ms:02}".replace(":", "-")
+
+
+def extract_frames(video_file, verbose=1):
+    # load the video clip
+    video_clip = VideoFileClip(video_file)
+    # make a folder by the name of the video file
+    filename, _ = os.path.splitext(video_file)
+    if not os.path.isdir(filename):
+        os.mkdir(filename)
+    # if the SAVING_FRAMES_PER_SECOND is above video FPS, then set it to FPS (as maximum)
+    saving_frames_per_second = min(video_clip.fps, SAVING_FRAMES_PER_SECOND)
+    # if SAVING_FRAMES_PER_SECOND is set to 0, step is 1/fps, else 1/SAVING_FRAMES_PER_SECOND
+    step = 1 / video_clip.fps if saving_frames_per_second == 0 else 1 / saving_frames_per_second
+    iteration = np.arange(0, video_clip.duration, step)
+    if verbose:
+        iteration = tqdm(iteration, desc="Extracting video frames")
+    # iterate over each possible frame
+    for current_duration in iteration:
+        # format the file name and save it
+        frame_duration_formatted = format_timedelta(timedelta(seconds=current_duration)).replace(":", "-")
+        frame_filename = os.path.join(filename, f"frame{frame_duration_formatted}.jpg")
+        # save the frame with the current duration
+        video_clip.save_frame(frame_filename, current_duration)
+    return filename, video_clip.fps
+
+
+
+def reverse_video(frames_path, video_fps, remove_extracted_frames=True):
+    frame_files = glob(os.path.join(frames_path, "*"))
+    # sort by duration in descending order
+    frame_files = sorted(frame_files, key=lambda d: datetime.strptime(d.split("frame")[1], "%H-%M-%S.%f.jpg"), reverse=True)
+    # calculate the FPS, getting the minimum between the original FPS and the parameter we set
+    saving_frames_per_second = min(video_fps, SAVING_FRAMES_PER_SECOND)
+    if saving_frames_per_second == 0:
+        # if the parameter is set to 0, automatically set it to the original video fps
+        saving_frames_per_second = video_fps
+    print("Saving the video with FPS:", saving_frames_per_second)
+    # load the frames into a image sequence clip (MoviePy)
+    image_sequence_clip = ImageSequenceClip(frame_files, fps=saving_frames_per_second)
+    # write the video file to disk
+    output_filename = f"{frames_path}-inverted.mp4"
+    image_sequence_clip.write_videofile(output_filename)
+    if remove_extracted_frames:
+        # if set to True, then remove the folder that contain the extracted frames
+        shutil.rmtree(frames_path)
+
+
+
+if __name__ == "__main__":
+    import sys
+    video_file = sys.argv[1]
+    frames_folder_path, video_fps = extract_frames(video_file)
+    reverse_video(frames_folder_path, video_fps=video_fps)
+