version 4.4 is converting youtube videos to mp3 instead of mp4

Just tried it and it downloads in MP4 OK for me (with Smart mode enabled)

Check your settings as this is where the default format can be set:

With Smart Mode enabled:
Tools
Smart Mode
Format
use the dropdown menu to select MP4 Video

With Smart mode not enabled:
When you paste the link, the window appears with all the different settings for that download.
Make sure that the format shows MP4 (although there isn't an option for MP3, so that isn't likely to be the reason for your problem

Personally, I normally use Smart Mode and have the settings preset, so I just have to paste the link and it automatically downloads using those settings