How can I insert my own video into the campaign prologue?

How do I insert my own video into the campaign prologue? I have Heroes 3 Shades of Darkness, and there are many standard videos and music files there, but I couldn't find any media files using the file explorer. I tried using ffmpeg – it's complete garbage! It only creates FLV files, and it can't even create MP4 files, let alone SMK files. A regular converter works better.