With URL Video Downloader, it's easy to download video from URL within your browser. If necessary, URL Video Converter can convert videos for use on your device directly like iPhone, iPad, or iPod. Of course, you can play it on your computer later, or whenever you want. Downloading video using url lets you benefits from watching video with no ads, no buffering and without Internet required.
I dont know, But many online video downloder helper are available.Assume if you cant download youtube videos from youtube,but you you dont worry,copy video URL and paste this type online video downloder helper website,and You can download different resolution and different size.Some this type wesite have extentions for chrome broser that can help or easily handle your video downloading.
And i suggest FDM(FreeDownloadManager)for youtube video downloading,this also have extension for chrome browser
Any video website has their own players and should special program for limit download data from them.
But with Internet Download Manager extention with chrome or Firefox browsers you can download the most whole of every sites that you want to download their videos.
Though I did not use such type of video downloader. But after a quick search on Google, I found this article, hope it will help you to find the best online video downloader. You can use the AceThinker, it's much better than others.