What happens when we Fast Forward the Video

I've been involved in Image Processing kind of project for the last couple of month, before which i had no experience in Image processing. While filtering the image today i had a thought what exactly happens when we fast forward any movie or a video clip ?

For example, If I have a video whose Frame rate is 30 , this means that 30 frames will be process in a second. and each frame will take 1/30 = 0.03sec to process , If we increase the frame rate or FPS of the video we will get more smooth view of it.

So what exactly happens when we fast forward the video, what i think is (not sure) the audio and the video of any clip must be synchronized so that we can control both accordingly.

So when we forward the video does it skip certain Frames ? if yes, then what about the Audio ? What exactly happens ?