Beta Custom key names may be used, but they MUST carry a hyphenated prefix to ensure that there will not be a namespace collision with future revisions to this specification. Clients SHOULD use a reverse-DNS syntax when defining their own prefix.
Optional duDuress
Key is included without a value if the server is under duress, due to cpu, memory, disk IO, network IO or other reasons. The thresholds for signaling duress are left to the discretion of the server operator. The intent is that the client will use this signal to move away to an alternate server if possible. This key MUST NOT be sent if it is false.
Boolean
Optional etpEstimated Throughput
The throughput between the server and the client over the currently negotiated transport as estimated by the server at the start of the response. The value is expressed in units of kilobits per second and rounded to the nearest integer. The time window for this estimate is expected to be the duration of the current response at most. The throughput may vary during the response and the client SHOULD use this data as an adjunct to its own throughput estimates. As an informative example, this estimate could be derived in this way:
etp = 8 * send_window / (rtt)
where send_window = min (cwnd * mss, rwnd) with Congestion Window (cwnd) measured in packets, Maximum Segment Size (mss) in bytes, Receiver Window (rwnd) in bytes and rtt in milliseconds. Note that multiple client processes adjacent to the media player may pool their requests into the same connection to the server. In this case the server estimate of throughput will be against the entirety of the connection, not all of which will be accessible to the media player.
Integer Kbps
Optional mbMax suggested bitrate
The maximum bitrate value that the player SHOULD play in its Adaptive Bit Rate (ABR) ladder. If the player is playing a bitrate higher than this value, it SHOULD immediately switch to a bitrate lower than or equal to this value.
Integer Kbps
Optional rdResponse delay
The time elapsed between the receipt of the request and when the first byte of the body becomes available to send to the client. The intention is for receivers to use this value to more accurately calculate the throughput of the connection [MHV22].
Integer milliseconds
Optional rttRound Trip Time
Estimated round trip time between client and server. This estimate may be derived from the transport handshake. For subsequent requests over the same connection, the value can be refined to be an exponentially weighted moving average of prior instantaneous values. An informative example algorithm for this averaging is provided by [18].
Integer Kbps
Common Media Server Data (CMSD) dynamic response header field parameters.
See
Spec