Making thumbnail mosaic from videos using Python and OpenCV

video_to_thumb_mosaic.py

from pathlib import Path
import cv2
import numpy as np

def make_mosaic(cap, n_rows=4, n_cols=5):
    n_frames = n_rows * n_cols
    cap_frames = int(cap.get(cv2.CAP_PROP_FRAME_COUNT))
    floor = int(cap_frames*0.05)
    ceil = int(cap_frames*0.95)
    frames_indexes = np.linspace(floor, ceil, n_frames).astype(int)
    frames = []
    for frame_index in frames_indexes:
        cap.set(cv2.CAP_PROP_POS_FRAMES, frame_index)
        success, frame = cap.read()
        if success:
            frames.append(frame)
    if n_frames != len(frames):
        raise Exception(f'Frame extraction error. Got {len(frames)}. Expected {n_frames}')
    rows_list = [frames[x:x+n_cols]
                 for x
                 in range(0, len(frames), n_cols)]
    rows = [np.hstack(row) for row in rows_list]
    mosaic = np.vstack(rows)
    return mosaic

def downscale(image, max_height=3500, max_width=3000):
    height, width = image.shape[:2]
    h_ratio, w_ratio = height/max_height, width/max_width
    ratio = max(h_ratio, w_ratio)
    if ratio <= 1.0:
        return image
    new_dim = int(width/ratio), int(height/ratio)
    return cv2.resize(image, new_dim, interpolation = cv2.INTER_CUBIC)

def save_mosaic(video_filepath, overwrite=True, **kwargs):
    video_filepath = Path(video_filepath)
    name = video_filepath.name
    base_name = '.'.join(name.split('.')[:-1])
    mosaic_name = f'{base_name}.jpg'
    mosaic_filepath = video_filepath.parent / mosaic_name
    if overwrite or not(mosaic_filepath.exists()):
        cap = cv2.VideoCapture(video_filepath.as_posix())
        mosaic = make_mosaic(cap, **kwargs)
        mosaic2 = downscale(mosaic, **kwargs)
        cv2.imwrite(mosaic_filepath.as_posix(), mosaic2) 
        
def batch_mosaic(folder,
                 video_suffixes=['.mp4', '.wmv', '.avi'],
                 **kwargs):
    folder = Path(folder)
    files = sorted(folder.glob('*'))
    video_files = [f for f in files
                   if f.suffix in video_suffixes]
#     video_files = video_files[0:2]
    for n, file in enumerate(video_files):
        print(f'Making mosaic {n+1}\n   {file.name}')
        try:
            save_mosaic(file, **kwargs)    
        except Exception as e:
            print(f'     {e}\n\n\n')
            
folder = Path().cwd()
batch_mosaic(folder, overwrite=False)