Add a subdirectory redirect - .htaccess

Question

I am trying to add a new path level to my search, for example:
wwww.website.com/s/blablabla/2
becomes
www.website.com/s/videos/blablabla/2
2 being the page.
However, I can't get this to work with htaccess because it keeps looping (I think that since /s/videos/ contains /s/ it keeps doing the rewrite...)
So far, I tried these codes:
RewriteCond %{REQUEST_URI} !^/s/.*$
RewriteRule ^(.*)$ /s/videos/$1 [L]
This give me the following error:
The requested URL /s/videos/index.php was not found on this server.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.
This code:
RewriteCond %{REQUEST_URI} ^/s/.*$
RewriteRule ^(.*)$ /s/videos/$1 [L]
Gives me the following error:
Internal Server Error
The server encountered an internal error or misconfiguration and was
unable to complete your request.
Please contact the server administrator,
webmaster#website.com and inform them of the time the error
occurred, and anything you might have done that may have caused the
error.
More information about this error may be available in the server error
log.
I also tried
RewriteRule !^s(/|$) s/videos%{REQUEST_URI} [L]
and
RewriteRule ^s/(.*)$ /s/videos/$1 [R=301,NC,L]
But none seems to work...
EDIT:
RewriteRule ^s/([A-Za-z0-9-\s]+)/?$ /s/videos/$1 [R=301,NC,L]
Is working but only if there is no page after the search tag...
EDIT2:
I was able to get it working by adding multiple lines for the different scenarios:
RewriteRule ^s/([A-Za-z0-9-\s]+)/?$ /s/videos/$1 [R=301,NC,L]
RewriteRule ^s/([A-Za-z0-9-\s]+)/([0-9]+)/?$ /s/videos/$1/$2 [R=301,NC,L]
Not sure if it's the proper way to do it at all though
if I do
RewriteRule ^s/(.*)$ /s/videos/$1 [R=301,NC,L]
It gives me
/s/videos/videos/videos/videos/videos/videos/videos/videos/videos/videos/videos/videos/videos/videos/videos/videos/videos/videos/videos/videos/videos/searchtag
EDIT3:
RewriteCond %{REQUEST_URI} !^/s/(videos|members|photos)
RewriteRule ^s/(.*)$ /s/videos/$1 [R=301,NC,L]
This is working...

Answer 1

Try this code.
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^s/([^/]+)/([0-9]+)/?$ /s/videos/$1/$2 [L]