These are not bugs, but features. The miniDV format is a glutton for hard disks. Dropping frames from the standard 24 frames per second to conserve disk space, leads to jerky movies. High frame compression creates blurry pictures. So does a poor-quality codec, a software that compresses and decompresses images.
You need a huge hard disk, better codecs, and maybe better software.
But first, please google-search the web for introductions and tech primers on digital video, which is a vast topic, and you need to understand its fundamentals well.