Please note some buffering is normal because the video is caching (loading) before it begins to stream the video. There are many factors that can affect video streaming quality including your Internet bandwidth. Please refer to this FAQ regarding how fast your Internet connection needs to be: 

http://support.digitaltutors.com/forums/114300/entries/109965

If you are experience any of the following: trouble playing a tutorial, error message received or you have experienced longer than normal buffering please follow these steps:

1) Clear your cache and your cookies. If you are unsure how to do so please refer to this FAQ:

http://support.digitaltutors.com/entries/20243851-i-m-having-issues-logging-into-the-site-or-i-m-being-logged-off-automatically-what-can-i-do

2) If you continue to experience buffering when playing a tutorial, please submit a support ticket. A member of our support team will reply within 24 hours. We request that you attach a screen shot along with the name of the tutorial you are viewing. 

http://www.digitaltutors.com/11/help.php