Video sites keep changing their coding and here are my current favorite methods for downloading a video from a stubborn website on my Windows 7 and 10 laptops.
I use the Opera browser on both laptops and 2 extensions which work together:
tampermonkey enables a convenient download arrow with format size options.
These two extensions also work together well on Chrome on my Windows 10 laptop but not my Windows 7 laptop.
More recently, the Chameleon Opera Add-on is an alternative for tampermonkey on both browsers:
(this combo worked on my Windows7)
A good substitute for this combo on either Chrome, Opera, or Firefox is the
Flash Video Downloader extension (FVD)
If all else fails, the last resort is Firefox Download Helper extension but I find Firefox very unstable on my laptops. Sometimes on FireFox, NetHunter produces a nice TS file from some sites
If your file does not play the audio, try playing the file on VLC
(if you hear the video on VLC, you can use VLC to convert the file to MP4 with audio)
Other extensions which may work nicely on some sites
Video Downloader Professional
Video Downloader Pro
For youtube, I still like the blue Freemake Video Downloader and gold Freemake Video Converter products but be careful when downloading and installing either to always choose custom options and uncheck any unwanted extra offers.
and always download from the official software sites!
Here are some sites that enable downloading by pasting a url:
http://en.savefrom.net/ (which also offers the nethelper extension)
to download from VK without any extension or software:
(1) go to the mobile VK site (type m.(dot) in front of vk.com or go to https://m.vk.com)
(2) play the video you want to download
(3) right click and choose "save video as"
(Note I work only with Windows Operating Systems and have not tried to download on MACs, etc)