diff --git a/utils/datasets.py b/utils/datasets.py
index 8d5fbb6a4a16..86a63786e17e 100755
--- a/utils/datasets.py
+++ b/utils/datasets.py
@@ -276,7 +276,7 @@ def __init__(self, sources='streams.txt', img_size=640, stride=32):
             # Start the thread to read frames from the video stream
             print(f'{i + 1}/{n}: {s}... ', end='')
             url = eval(s) if s.isnumeric() else s
-            if 'youtube.com/' in url or 'youtu.be/' in url:
+            if 'youtube.com/' in url or 'youtu.be/' in url:  # if source is YouTube video
                 check_requirements(file=None, include=('pafy', 'youtube_dl'))
                 import pafy
                 url = pafy.new(url).getbest(preftype="mp4").url