Scripting with VirtualDubMod - Google it, but if your files are flv, then it would take you two extra steps;
I used to use scripting with VirtualDubMod to strip a single frame from videos when I was P2P spamming back in the day; I would load one video watermarked with my URL, then clone it to hundreds of vids by removing a single frame each time, then batch renaming them with some kinky titles and finally leaving them in a folder that was shared by 5-6 P2P programs that I was running