What is the crowd's opinion of Video Crop?

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I'm trying to combine some portrait videos together but my problem is that the videos are put onto a landscape frame, meaning they've got black bars either side. I want to be able to combine the two portrait videos and keep the portrait orientation.

I've found a workaround where I simply crop the video using Video Crop, but the problem with that is the frame rate is quite bad.

Anyone know any apps I can use to achieve this?