Change aspect ratio from 16:9 to 4:3
 

I have shot my footage with a 16:9 ratio and want to change it to 4:3 for my final output. At the same time, I want to add one word subtitles to the bottom of the video to fit to the new size- doing two things at once. Is there any easy way to do this? I have tried a couple approaches but they seem to be giving me undesirable artifacts. Thanks.