Youtube urls and other video sites urls, why that way ?

[eluser]Twisted1919[/eluser]
As the title say, i am trying to understand, what's the reason why, for example youtube uses urls like :

Code:

http://www.youtube.com/watch?v=uelHwf8o7_U

instead of :

Code:

http://www.youtube.com/watch?v=1234567

I mean, what's the real reason why they are not using the database ID of the video, and they are using a random string ?

On the other hand, vimeo uses something like : http://vimeo.com/15261921 , so it's the database id .

[eluser]CroNiX[/eluser]
you have infinitely more possibilities using upper/lowercase letters in addition to numbers. Also, who is to say that the random upper/lowercase letters+numbers isn't a unique db ID field? It is after all, unique.

[eluser]Jônatan fróes[/eluser]
it works like short url systems:

Code:

ex:
1 = a
2 = b
...
10 = j
25 = z
26 = A

This way the urls won't be so large.

[eluser]Twisted1919[/eluser]
Thank you both, while waiting for the reply here i made a some research and i found this article:
http://kevin.vanzonneveld.net/techblog/a...r_tinyurl/
which explains why these are used and of course how to create and use them.
Basically is like Jonatan says, the database id is converted into a string then you can convert the string back so that you can use the database id .
Another advantage is that if you use them , the urls won't be predictable anymore so this stops automated crawlers/boots/harvesters to look into your site.