Welcome to the forum! I think you're seeing the dreaded "dropped frames" with your capture tools. Either video/audio sync configuration is causing it, or you have insufficient CPU power to capture with the settings you are using -- color space, resolution, codec configuration, etc. There are lots of things I don't know -- capture card, drivers, capture configuration, capture software, video encoding codec, codec configuration -- so I can't give you a specific recommendation. If you check out the "Capturing video" forum, you'll find a FAQ, which is a great place to start!