parse_url doesn't works if the protocol doesn't specified. This seems like sandard, even the youtube doesn't gives the protocol name when generates code for embedding which have a look like "//youtube.com/etc".

So, to avoid bug, you must always check, whether the provided url has the protocol, and if not (starts with 2 slashes) -- add the "http:" prefix.