Specifies the peak bit rate, in bits per second, used for constrained 2-pass variable-bit-rate (VBR) playback.

Constant for IPropertyBag


Data Type


Default Value

No default.


This value represents the peak bit rate for playback. The value of MFPKEY_BMAX is used to describe the buffer in terms of this bit rate; in effect, constrained VBR is similar to constant bit rate (CBR) using this value as the bit rate. However, a constrained VBR stream can be played back at a lower bit rate, as long as the buffer is increased.

You must set this value for peak-constrained two-pass VBR encoding. After you begin processing samples, you must not query for this value until you are finished encoding the stream. The encoder interprets a request for this value as a signal that the encoding session is over; the next sample that you process is treated as the beginning of a new session.

Typically, this value is two to three times greater than the value of MFPKEY_RAVG.


Minimum supported client
Windows XP [desktop apps only]
Minimum supported server
Windows Server 2003 [desktop apps only]

See also

Media Foundation Properties