nessViewer media presentation extensions
External extension are used for the various video formats which can be displayed in a media presentation.


Adobe Flash

The "Flash Player" displays internet videos based on the "FLV" (Flash video) and "SWF" (Shockwave Flash): for example videos of YouTube.
→ Adobe Flash web page

Apple QuickTime

"QuickTime" displays many internet videos and local media in various file formats.
QuickTime is usually integrated in all macOS versions.
→ Apple support web page


Telestream Flip4Mac

"Flip4Mac" is an "QuickTime" extension to display "WMV" (Windows media) videos.
→ Flip4Mac web page (up-to-date)
→ Download Flip4Mac (free of charge)

Perian

"Perian" is an "QuickTime" extension to display video formats like AVI, DivX, MKV.
→ Perian web page
→ Download Perian

Each extension must be installed after the download.
Flip4Mac is only free of charge up to version 3.2.x. If the link redirects to a newer version, then it might be recommendable to search for a older version.