As with any art you should study some other people's combo videos and take inspiration from them to make your own. Use reference in any creative medium, whether it be in music, programming, video editing or in my case video game art. Always look up and see what other people did and why those people were successful. You already do it all the time when trying to get better at your character, do the same for when you want to improve on things like video editing.
I bring this up because the first thing that people do when making videos is that they always play with the baked in transitions in their editor program... however all of them are bad and distracting. I understand the thought process behind making the transition and trying to make it look good... you think that "Well, I need SOMETHING between these clips, what should I put here?"... and so you put something there. It's just filler though and it's only causing the audience's attention span to go "Clip -> Transition -> clip -> transition" which... you really should be focusing on making the audience only focus on the clips.
So, my advice is to get rid of the transitions all together. They do not add anything of value to the video. They only serve to distract people from the actual content that they came here for (the combos!)
If you want to up your editing game one thing you can do to get around having to overlay music over the whole thing is that whenever you're playing friendlies and capturing you should turn off the music in the game itself, but keep the SFX on. That way you can add the music in during the editing phase and have one cohesive song throughout the video, but still keep the SFX which add a lot to the effect of a combo video in my opinion. Similarly, you could just tone down the music to be fairly quiet in the game and boost the SFX way up so that when you're playing it doesn't sound as dead haha.
Final tidbit is to fix your black border issue. I had a similar issue years ago where my capture was recording with weird black bars at the top and bottom, but then when I'd go to export I'd select a 16:9 format and it'd put black borders on the sides as well. Look into your black border problem and solve it!
Check out other popular combo videos and learn from them. (Here's a pretty good example
https://www.youtube.com/watch?v=2Oz9J9hhEXo )This stuff will come easier over time. Best of luck man.
Also, I hope I don't come across as mean or anything. Purely trying to be helpful. I know starting out on any new creative medium can be intimidating, and so it's easy to see feedback and take it as an attack. I only aim to help, so keep going man.
