YouTube – web-profile

download video from YouTube:

Add to YouTube link "ss" before word "youtube".
So: http://www.youtube.com/watch?v=pRpeEdMmmQ0 becomes http://www.ssyoutube.com/watch?v=pRpeEdMmmQ0

Flag Youtube video as inappropriate => Select reason => Spam => misleading thumbnail:

YouTube video with high quality

http://www.youtube.com/watch?v=pRpeEdMmmQ0_&hd=1
http://www.youtube.com/watch?v=pRpeEdMmmQ0_&vq=hd720
http://www.youtube.com/watch?v=pRpeEdMmmQ0_&vq=hd1080

240p: &vq=small 
360p: &vq=medium 
480p: &vq=large 
720p: &vq=hd720 
rel=0
fs=1
showinfo=0
autohide=1

YouTube video with autoplay

YouTube video with loop

YouTube video with time param

YouTube video with other params

https://youtube.com/watch?v=bvLQZVnz5WM%3Fshowinfo%3D0%26iv_load_policy%3D3%26modestbranding%3D1%26nologo%3D1%26vq%3Dlarge%26autoplay%3D1%26amp%3Bps%3Ddocs

YouTube thumbnails

Each YouTube video has 4 generated images. They are predictably formatted as follows:

http://img.youtube.com/vi/pRpeEdMmmQ0/0.jpg
http://img.youtube.com/vi/pRpeEdMmmQ0/1.jpg
http://img.youtube.com/vi/pRpeEdMmmQ0/2.jpg
http://img.youtube.com/vi/pRpeEdMmmQ0/3.jpg

The first one in the list is a full size image and others are thumbnail images. The default thumbnail image (ie. one of 1.jpg, 2.jpg, 3.jpg) is:

http://img.youtube.com/vi/<insert-youtube-video-id-here>/default.jpg

For the high quality version of the thumbnail use a url similar to this:

http://img.youtube.com/vi/<insert-youtube-video-id-here>/hqdefault.jpg

There is also a medium quality version of the thumbnail, using a url similar to the HQ:

http://img.youtube.com/vi/<insert-youtube-video-id-here>/mqdefault.jpg

For the maximum resolution version of the thumbnail use a url similar to this:

http://img.youtube.com/vi/<insert-youtube-video-id-here>/maxresdefault.jpg

All of the above urls are available over https too. Just change http to https in any of the above urls.

Video example:

Thumbnails from video: