Open VBA editor (Alt-F11). In the immediate window, type the following code, replacing ‘x’ with the appropriate Slide and Shape indices:

? Application _
.ActivePresentation _
.Slides(x) _
.Shapes(x) _
.LinkFormat _
.SourceFullName

This will output the full path information to the linked media file. To change the path, such as in the case of removing full path information and leaving just the filename, use the following syntax:

Application _
.ActivePresentation _
.Slides(x) _
.Shapes(x) _
.LinkFormat _
.SourceFullName = "mediafile.mpg"