There are two ways for you:
1. Use a PC software, like Gihosoft TubeGet, a free yet practical YouTube downloader. You use it to download YouTube videos to your computer, then transfer the videos to your memory card.
2. If you are using a mobile device, like Android or iPhone, you can use the app such as TubeMate to download the videos directly to your smartphone.
You can use NoteBurner YouTube Video Downloader, a handy tool that helps you save youtube videos in MP4 or MKV format. After the video has been saved in MP4/MKV format, you can transfer it to your memory card.
teach me how to download
Download it to your computer and then save into the memory card
A video card or video adapter translates binary data into images.
just Graphic memory (GDDR)
Not usually. Video card memory generally consists of ROM chips soldered directly to the card, so if the graphics card goes bad, it's best to replace it.
no you can't
moose!
A video card is hardware, and as such cannot be downloaded because it is a physical thing. Perhaps you meant to ask about video card drivers, which certainly are available for download.
Memory card adapters are designed to be used with a personal computer, so that they can, indeed, download pictures to your PC.
This will depend on the resolution of your video, and the format of the video. On average, about 4 hours of 720p HD video can be held on an 8GB memory card.
the memory between the video card and the mother board DO NOT need to match. the memory on the vid card CANNOT be upgraded.