It works

According to Karoliina:

"As a matter of fact the hildon-welcome is fully configurable.
You don't need to remove/replace the Nokia hands animation file to add your own animation or sound to the startup. Hildon-welcome supports unlimited number of "logo animations" (either video or image+sound) in sequence. It reads all configuration files in the hildon-welcome.d folder and interprets them in alphabetical order. "

Instructions:

1- Copy the video to /usr/share/hildon-welcome/media
2- Go to /etc/hildon-welcome.d/ and edit the default.conf file or create a similar one (the videos will play by the alphabetic order of the .conf files)