If you reference the same external file from several places in your document, you can dedicate a hotspot character format to this purpose. You assign property MacroHot to the character format, and provide a definition for the macro. For example:
[HelpMacroStyles]
ShowAvi=EF('yourname.avi')
DITA2Go provides a predefined WinHelp macro. For example:
[HelpStyles]
FarTarget=MacroHot
[HelpMacroStyles]
; Topic Macro and MacroHot have a required macro content
FarTarget=EF(http://www.omsys.com/)