Apologies if this is a duplicate post, but nothing I've read on any of the others has worked. I've imported various video (recorded at 30 fps) and audio strips into Blender's video editor and when trying to preview the result, the fps drops to 5-10 fps, making aligning the video and audio impossible.
Playing the videos through a few times
Installing the latest graphics drivers (already installed)
Increasing the memory cache limit in system preferences
Giving Blender high priority in task manager
Lowering the output resolution (helps but is unusable)
Changing the sync mode to frame dropping and AV-sync
Trying different output video codecs
I'm using Blender v2.79 on Windows 10 x64 and importing .mov video files and .wav audio files.
First, make sure Blender is using the same resolution as your input video in the timeline.
If you're still slow, then it's probably time to generate proxy files. You're probably trying to edit a compressed video type instead of a RAW video type. By making proxy files, you get around this issue.