Extract specific frames of youtube video without downloading video

Question

I need to extract specific frames of an online video to work on an algorithm but I don't want to download the whole video because that would make it highly inefficient.

For starters, I tried working with youtube videos. I can download whole of the video using youtube-dl in this way:

ydl_opts = {'outtmpl': r'OUTPUT_DIRECTORY_HERE',}
with youtube_dl.YoutubeDL(ydl_opts) as ydl:
    ydl.download([url])

And then I can capture individual frames.

I need to avoid downloading the whole video. After some research, I have found that ffmpeg might help me do this. I found no way to download just the frames so if this is not possible, the second option is that I can download specific portions of the video. One such example in linux is here but I couldn't find any solution for python.

What is a good way to download just the frames, or portions of videos (in python) without downloading the entire thing?

Answer 1

Just to add on to the current answer, performance can further be enhanced using multiprocessing. For example, if you wanted to split up the video into frames and process them independently in num_cpu processes:

import os
from functools import partial
from multiprocessing.pool import Pool

import cv2
import youtube_dl

def process_video_parallel(url, skip_frames, process_number):
    cap = cv2.VideoCapture(url)
    num_processes = os.cpu_count()
    frames_per_process = int(cap.get(cv2.CAP_PROP_FRAME_COUNT)) // num_processes
    cap.set(cv2.CAP_PROP_POS_FRAMES, frames_per_process * process_number)
    x = 0
    count = 0
    while x < 10 and count < frames_per_process:
        ret, frame = cap.read()
        if not ret:
            break
        filename =r"PATH\shot"+str(x)+".png"
        x += 1
        cv2.imwrite(filename.format(count), frame)
        count += skip_frames  # Skip 300 frames i.e. 10 seconds for 30 fps
        cap.set(1, count)
    cap.release()



video_url = "..."  # The Youtube URL
ydl_opts = {}
ydl = youtube_dl.YoutubeDL(ydl_opts)
info_dict = ydl.extract_info(video_url, download=False)

formats = info_dict.get('formats', None)

print("Obtaining frames")
for f in formats:
    if f.get('format_note', None) == '144p':
        url = f.get('url', None)
        cpu_count = os.cpu_count()
        with Pool(cpu_count) as pool:
            pool.map(partial(process_video_parallel, url, 300), range(cpu_count))

For the purposes of this application, since images are just being saved from the video, this may not result in a huge improvement (maybe a few seconds), but if additional algorithms needed to be applied on the frames, it could be beneficial.