Javascript regular expression for extracting Youtube video ids

Question

The following code is used to get Youtube video ids in order to get a thumbnail image.

What is the reasoning behind the first regular expression and what is it doing

Answer 1

"[\\?&]v=([^&#]*)"

explained (after reduction from a JavaScript string to a regex):

[\?&]   # Match a ? or a & (the backslash is unnecessary here!)
v=      # Match the literal text "v="
(       # Capture the following into backreference no. 1:
 [^&#]* # Zero or more characters except & or #
)       # End of capturing group.

The second regex [^http://youtu.be/](.*)[^?hd=1] is very wrong.

It probably should read

"^http://youtu.be/(.*)(?=hd=1)"