Some days ago I learned how to subtitle a Video with hard-subs; even tough I achieved to do it in this way, I think there may exist a more straightforward method. I would have used kdenlive but since I use Gentoo I think a command line method is the correct one because I want to avoid everything related to KDE in my Gentoo.

Step one. Create an mp4 with soft-subs:

The additional step I did was because I needed to specify the encoding for my Spanish subs (ISO-8859-1) , because if you try only the burn the subtitle using only the second step it will ask you to use -sub_charenc parameter.

The maps parameters are important since they mean that the video track plus the subtitle track and the audio track will be all included.

Step two. Create the hard-subs