Moving data from the_content() to postmeta

This is more of a MySQL question, and I apologize if this is not the right forum, but here’s what I need help doing:

Take a variable string that appears in many (but not all) of the posts:

e.g. flv=”http://mysite.com/filename.flv”

extracting just the filename.flv part

placing it into a row in the postmeta table that includes a meta id, post id, a custom field name, and the filename. This would cover the four columns in postmeta:

meta_id post_id meta_key meta_value