In my program I introduced an if_statement, which includes more than one condition (3-4). Apparently, the if_statement looks only to the first condition and not to the others. This determines that if the first condition is satisfied and not the others, the video is processed as well.
I ascertained it just mixing the different conditions and every times the first works as the only accepted condition and the others (second,third,etc.) are neglected.
So, instead of using an if_statement with 3 conditions, I use 3 if_statement with a single condition, and it works.