Un fichier asx n'est pas un fichier vidéo (ni audio) mais:
"Goal: Create a simple ASX file to play Windows Media in the external
Windows Media Player.
A simple, yet effective method of playing Windows Media, is to simply
reference an ASF Stream Redirector file (ASX). An ASX file is an
eXtensible Markup Language (XML) based text file which references a
Uniform Resource Locator (URL) for a piece of media content. Simply
put, an ASX file is a shortcut to Media Content."