I\'m having a hard time, searching how to play a video file from a TMemoryStream (or a similar buffer in memory) using FFMpeg. I\'ve seen many things, including UltraStarDX,
You can waste your time rewriting FFMPEG from C++ to Delphi, or mess with wrapper libraries.
Or if you're just interested in playing a video in Delphi, then check out Mitov's VideoLab components.
http://www.mitov.com/products/videolab#components