MPEG-encoded variable bit rate (VBR) video traffic is expected to incur cell losses during its transmission over a broadband network. These cell losses introduce distortion into the received video. Frame drop rate and root mean square error (RMSE) can be used to objectively measure this distortion. These two metrics are useful in identifying the threshold cell loss rate (CLR) beyond which the quality of received video is unacceptable to viewers. Thus, they are useful in identifying CLRs to be used in evaluating VBR video traffic models. A novel analytical model is developed for predicting both frame drop rate and RMSE as a function of (i) uniform cell loss rate and (ii) MPEG encoding parameters. The model is validated by an empirical study using an actual MPEG video.