First, verify that the mod_rewrite module is installed. Then, be careful to understand how it works, many people get it backwards.
You don't hide URLs or extensions. What you do is create a NEW URL that directs to the old one, for example
The URL to put on your web site will be yoursite.example/play?m=asdf
or better yet
yoursite.example/asdf
Even though the directory asdf doesn't exist. Then with mod_rewrite installed you put this in .htaccess. Basically it says, if the requested URL is NOT a file and is NOT a directory, direct it to my script:
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ /play.php [L]
Almost done - now you just have to write some stuff into your PHP script to parse out the new URL. You want to do this so that the OLD ones work too - what you do is maintain a system by which the variable is always exactly the same OR create a database table that correlates the "SEO friendly URL" with the product id. An example might be
/Some-Cool-Video (which equals product ID asdf)
The advantage to this? Search engines will index the keywords "Some Cool Video." asdf? Who's going to search for that?
I can't give you specifics of how to program this, but take the query string, strip off the end
yoursite.example/Some-Cool-Video
turns into "asdf"
Then set the m variable to m=asdf
.
So both URLs will still go to the same product
yoursite.example/play.php?m=asdf
yoursite.example/Some-Cool-Video
mod_rewrite can do lots of other important stuff too, Google for it and get it activated on your server (it's probably already installed.)