If your computer struggles to play back your timeline smoothly, use the ‘preview quality’ option above the preview window to try and speed it up. Below we’ve selected ‘Good – auto’ to see if it helps. Note this setting won’t affect the quality of any final renders/exported videos.

As discussed in the explainer, there are lots of export ‘codecs’ available to use with Vegas, and each is configurable to your precise requirements. Have a look here for detailed information.