Expected Behavior
When attempting to configure a constant bitrate stream, the Video Profile Encoding Mode must be set to Constant Bitrate:
With this configuration, the encoded video will be Constant Bitrate. However, unless the Audio Profile Encoding Mode is also set to Constant Bitrate, the overall muxed output will be Variable Bitrate.
Only when all sources of a stream (Video and Audio) are configured for Constant Bitrate will the overall output be muxed as a Padded CBR.