Merge Video with seperate music and subtitles

[BlackMamba]

Hello,
I am making a little application where you can select one video, then chose some audio and subtitles to mix with.
Then, once validated, the video is a mix of the original video with the audio and the subtitles directly mixed in.
You can then share the video on youtube for example and the audio/subtitles will be merged within the video.
Is it something that can be done with Qt Multimedia functions?
Cheers