In tests, I had to make a switch from MP4 to MKV format to get my test video to download in 4K. 4KVD snagged the 579.4MB file in about 43 seconds. It defaults back to 1080p HD, so I made the same switch when downloading an Ultra High Definition (8K) playlist. If you enable the Smart Mode and its pre-sets, 4K Video Downloader can then do one-click downloads to your favorite format. If you want to download more than 25 videos at a time or subscribe to YouTube channels to instantly download the latest, that requires the $15 paid version. Playback of the MKV file via VLC Media Player was flawless.
Using a strong password is a good way to protect your YouTube channel and Google account, but it's often not enough. The best way to secure your YouTube and Google account from hackers is to use Google's 2-Step Verification, which utilizes something you know (your password) and something you have (your phone). To login to your account, you'll need to enter both your password and a temporary code that Google sends you via text message or voice call on the phone. I highly recommend you enable 2-Step Verification for your Google account. Here's a step-by-step tutorial on how to enable and setup 2-Step Verification on your Google account and YouTube channel.