FLV for animation export in Animate

Hi Everyone,

I'm using the last version of animate and I would like to export my animation with the video behind, but I imported my video as H264 and it doesn't appear in the export I did in animate. I understand that I have to import a flv to be able to export it with my animation. The problem is : how to do convert a mov as flv ? media encorder doesn't do it. 

Do you a software that can do it ? (and not an internet website ahaha)

Many thanks by advance,

Carole