Hey Dainis..... I think you are making this way way too complicated ...certainly more than it actually needs to be. Full disclosure.... I didn't watch the entire video.... I did what some others did.... jump around enough to know that you are not understanding how to use this program effectively.....so....lets see if we can get you on the right path.

The issue at 13 minutes is I think you imported the midi which was in the key of B major with 5 sharps but you had the program set to it's default of C. So it was playing in 2 different keys at the same time. Yeah that's gonna sound wonky.

Another issue..... it's extremely rare to have a song with varying tempo. You pick one tempo and the entire song (with very few exceptions) stays at that tempo. You can change the power and feel of the song by using DYNAMICS which is changing the level of the verse in contrast to the chorus which generally has more power. You can also use volume to bring certain instruments in and out to play with the dynamics. Drummers for example would use side stick on the snare in the verses and smack the snare in the chorus to bring up the dynamics.

DO NOT START WITH AN IMPORTED AUDIO FILE..... man that's NOT the way to do this when you are beginning. Heck, I've been using this for over 15 years and I don't try to do that. Build the song IN the program first and THEN you can add your audio and live instruments to it. You mentioned that your audio was varying in it's tempo..... THAT is a major faux pax..... The program is wanting to find the tempo and stick with it.... it's not designed to change or follow the tempo of an audio file. When I work with people on their songs and they send me an audio file... the first thing I ask is did they use a click track and what is the exact tempo.

The best way to get started with BB ( Band in a Box) is to populate the time line with the chords and then select a style that fits closely to what you envision for the song. I actually pick the style first. Then you start on the intro.... 4 to 8 bars max....and then the first verse. When the first verse is correct, you can simply copy and paste it for the remaining verses. Then you input the chords to the chorus and use copy and paste to replicate it a second time if needed. You can easily edit the structure, change the tempo, change the key, and change the style as needed.

I hope this helps you out.... this is actually a fairly easy program to use one you get the basics. ALSO: Don't forget to use the PG support videos. They are short and to the point on helping you with individual aspects of working with this program.

Give that a try and let us know how you're doing. Any questions? Just ask.

You can find my music at:
www.herbhartley.com
Add nothing that adds nothing to the music.
You can make excuses or you can make progress but not both.

The magic you are looking for is in the work you are avoiding.