youtube4kdownloader, the famous online video download service, boasts itself as the best tool to fast yet conveniently download 4K Ultra HD videos from multiple video sites. And it offers you with 3 options: browser extension, bookmark and online website.
I've tried browser extension, which is the most convenient way to free download video (4K), indeed. When you find a video resource, the green download video button appears. Currently, it supports YouTube, facebook, etc. 7 video sites. But the downside is that it keeps loading and gets stuck on downloading video at 4K 3840x2160p videos, though no problem in downloading 1080p or 720p videos. The same issue also occurs to bookmark and online website, with error saying "network error". Well, the bandwidth network is actually running normally in speed.
On top of that, there are also other issues, including constantly pop up commercial ads banner, porn ad banner even though you close them, webpage re-direction, etc.
Finally, I'm worn out. Chuck this online service. Instead, resort to a professional 4K video downloader for PC program to free download 4K ultra HD videos in bulk without network error or fake 4K download issue.
Read more details if you're interested in: https://www.winxdvd.com/streaming-video/best-free-4k-video-downloader.htm