18.104.22.168.2 Buffer Size Attribute (a=bufsize)
The bufsize attribute is defined for use at the SDP media level. It specifies the buffer window that corresponds to the bit rate specified in the b=AS attribute defined in section 5.8 of [RFC4566] when the b=AS field is present at the SDP media level.
If there is no b=AS field at the SDP media level, then the meaning of the bufsize attribute is undefined.
The syntax of the attribute is defined as follows.
bufsize = "a=bufsize:AS=" buffer-window buffer-window = 1*10DIGIT
The buffer-window parameter specifies the amount of data that is required to be buffered by clients if they are receiving the data at the bit rate given by the b=AS field. The value of the buffer-window parameter is expressed in millisecond time units. The valid numerical range of the buffer-window parameter is from 0 to 4,294,967,265, inclusive.