Youtube Regex

This is the regular expression
^(http(s)??\:\/\/)?(www\.|m\.)?((youtube\.com\/watch\?v=)|(youtu.be\/))([a-zA-Z0-9\-_]+)$
This could also work since all youtube video id is 11 character
^(http(s)??\:\/\/)?(www\.|m\.)?((youtube\.com\/watch\?v=)|(youtu.be\/))([a-zA-Z0-9\-_]{11})$

It matches the following
https://www.youtube.com/watch?v=DFYRQ_zQ-gk
http://www.youtube.com/watch?v=DFYRQ_zQ-gk
www.youtube.com/watch?v=DFYRQ_zQ-gk
https://youtube.com/watch?v=DFYRQ_zQ-gk
http://youtube.com/watch?v=DFYRQ_zQ-gk
youtube.com/watch?v=DFYRQ_zQ-gk
https://m.youtube.com/watch?v=DFYRQ_zQ-gk
http://m.youtube.com/watch?v=DFYRQ_zQ-gk
m.youtube.com/watch?v=DFYRQ_zQ-gk
https://youtu.be/DFYRQ_zQ-gk
http://youtu.be/DFYRQ_zQ-gk
youtu.be/DFYRQ_zQ-gk

Note.
Get the video id and create yours.
try this

function extractVideoID(url){
    var regExp = /^.*((youtu.be\/)|(v\/)|(\/u\/\w\/)|(embed\/)|(watch\?))\??v?=?([^#\&\?]*).*/;
    var match = url.match(regExp);
    if ( match && match[7].length == 11 ){
        return match[7];
    }else{
        alert("Could not extract video ID.");
    }
}

https://ctrlq.org/code/19797-regex-youtube-id

Remember to match before editing: https://regexr.com/3ppe2

Use the following link to get the img of a youtube video
https://stackoverflow.com/questions/2068344/how-do-i-get-a-youtube-video-thumbnail-from-the-youtube-api

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

https://img.youtube.com/vi/<insert-youtube-video-id-here>/0.jpg
https://img.youtube.com/vi/<insert-youtube-video-id-here>/1.jpg
https://img.youtube.com/vi/<insert-youtube-video-id-here>/2.jpg
https://img.youtube.com/vi/<insert-youtube-video-id-here>/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:

https://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:

https://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:

https://img.youtube.com/vi/<insert-youtube-video-id-here>/mqdefault.jpg
For the standard definition version of the thumbnail, use a url similar to this:

https://img.youtube.com/vi/<insert-youtube-video-id-here>/sddefault.jpg
For the maximum resolution version of the thumbnail use a url similar to this:

https://img.youtube.com/vi/<insert-youtube-video-id-here>/maxresdefault.jpg
All of the above urls are available over http too. Additionally, the slightly shorter hostname i3.ytimg.com works in place of img.youtube.com in the example urls above.

Alternatively, you can use the YouTube Data API (v3) to get thumbnail images.