The sample accepts variable bit rate (VBR) sources. However, when comparing the profiles of the two VBR sources, the sample ignores the average bit rate difference because two VBR streams will have different average bit rates even if they were created using the same profile. WMVAppend cannot compare the peak bit rate of unconstrained bit-rate-based VBR streams, or the quality level of quality-based VBR streams, because this information does not exist in the source files. It is therefore the user's responsibility to make sure that two source files are created using the same profile. Otherwise, invalid content can be created.