The maximum number of consecutive B frames between I and P frames.
Set a value of 0 to disable B frames. Set a value of 1 or greater to enable B frames. If you use the Baseline profile, the number of consecutive B frames is always zero. The encoder overrides nonzero values.
_Windows:_ The maximum number of B frames allowed is 2.
_macOS:_ Set a nonzero value to enable B frames. When B frames are enabled, you cannot control the maximum number of B frames.