The upload uses is just a multipart HTTP post; just as you would get from
a web form with a file upload field.

In the settings, set Upload/Publish UrlBase to your cgi-bin directory
(including the slash) and the Upload/Publish script to the script name
(e.g., put20.pl).

Log files are uploaded as a single file; media include the media file and
a metadata chunk, encoded in XML.

put20.pl shows how to just store the files

vcput.pl shows how to parse metadata chunks