During the play back of you video project the video becomes choppy or the audio is out of sync.
When previewing your video project it takes up a lot of system resources and one way to reduce the strain on your system is to enable Smart Proxy
Enabling Smart Proxy
Proxy files are lower resolution working copies of video files. They are reduced in resolution or compression bit rate for only one reason -- to speed up editing of high definition files such as HDV, AVCHD, etc.
Proxy files are source-dependent rather than project-dependent. In other words, proxy files can be shared among different projects. Smart Proxy can also be used in other video file formats and is not limited to HDV files only.
The main purpose of this feature is to have a more efficient editing experience by making smaller proxy files out of large videos. When you edit and preview your project in Instant Play mode, proxy
files will be used as substitutes for their large video source counterparts. Whereas when you preview your project in high-quality playback mode or when you render a video file, the original video source files will be used.
To enable the creation of proxy files, go to File: Preferences - Smart Proxy, then select the Enable Smart Proxy option. In the Smart Proxy tab of the Preferences dialog box, you can set the condition when proxy files need to be generated and choose a proxy file format. Or you can also click the smart proxy icon in the Toolbar and select Enable Smart Proxy. Select Settings to customize Smart Proxy settings.
'For more information regarding smart proxy file and settings please refer to page 79 of the user manual'.