Q. When I animate a scene I receive a vbv overflow error. What can I do to prevent this?

VBV is the Video Buffer Verifier. It is a subsystem which checks the output of the MPEG encoder to ensure the information is constrained to the Constrained Parameter Bitstream (CPB) specification used by most MPEG decoders. This CPB specifies a limit of 101,376 (396 macroblocks) pixels per frame if the frame rate is 25fps or lower, and 84,480 pixels (330 macroblocks) per frame for rate of 30fps or lower. The defacto standard resolutions used is 352x240x30fps and 352x288x25fps. The MPEG standard itself does not actually have this constraint, it is the majority of decoders which are available.

AVS/Express v5.1 now recognizes an environment variable, XP_MPEG_PARAM_FILE, identifying the file containing the parameters to be used in MPEG encoding by the image_capture macro.  If the specified file does not exist, it will be created during the encoding process.  If it does exist, the parameter values it contains are used for encoding.  This allows you to let AVS/Express define the parameters in the file initially and then edit the parameters in that file as desired.   XP_MPEG_STATS can be used to define a file to hold data from the encoding process.
Window users who are experiencing problems with AVS/Express MPEG encoding may wish to create an AVI file with AVS/Express and use a third party tool to convert it to MPEG.

For versions prior to AVS/Express v5.1 (v5.0 and below), here are some thoughts on how to alleviate the problem.
When you first bring the viewer up it is most likely set to 500x500 pixels. This can change by resizing the window it is in. The larger the window the more pixels per frame you have to deal with. The problem is not actually with the size but the amount of pixels which change from frame to frame. Thus periods of lots of activity in the viewer are more likely to cause an overflow.

One way to prevent this is to reduce the viewer size. This can be done by resizing the whole window. A more precise method is to enter the Viewer user interface and change the viewer size manually. If you are using a SingleWindowApp or a MultiWindowApp template, you will find this under the Editors menu for View. Under the 'General' panel you should see two typein boxes labeled width and height. Changing these will change the viewer size.