RTCRtpEncodingParameters - Web APIs
other parameters may further constrain the bit rate, such as the value of maxframerate or transport or physical network limitations.
... maxframerate a double-precision floating-point value specifying the maximum number of frames per second to allow for this encoding.

RTCRtpSendParameters.encodings - Web APIs
other parameters may further constrain the bit rate, such as the value of maxframerate or transport or physical network limitations.
... maxframerate a double-precision floating-point value specifying the maximum number of frames per second to allow for this encoding.

RTCRtpEncodingParameters.maxBitrate - Web APIs
other parameters may further reduce the bandwidth used by the track; for example, maxframerate will, if set low enough, constrain the bandwidth as well.

RTCRtpSender.setParameters() - Web APIs
rangeerror the value specified for scaleresolutiondownby is less than 1.0, which would result in scaling up rather than down, which is not allowed; or one or more of the specified encodings' maxframerate values is less than 0.0.