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Home Ask the Expert Using FaultLine Why doesn't FaultLine measure MDI (Media Delay Index)?

Why doesn't FaultLine measure MDI (Media Delay Index)?

FaultLine does not include MDI statistics because they are only valid for constant bit rate (CBR) video streams while we are predominately seeing variable bit rate (VBR) network implementations.

We are very familiar with the MDI measurement, having implemented it in other (OEM) products, and will be happy to add it to FaultLine when the need arises, as we know there are CBR streams in use.

Additional information:

The MDI subset (RFC-4445) is a useful quality indicator for constant bit rate compressed video but is not defined for to variable bit rate stream networks. This is a somewhat contentious topic in the industry, so we are proceeding cautiously. MDI was always touted as a relatively simple measurement to make and scale to hundreds of channels.

The MDI RFC only specifies how to measure MDI for CBR streams.  The complexity of the measurement in VBR systems goes up dramatically however--as IneoQuest (RFC sponsor) has acknowledged in their formal publications.

The MDI consists of two components: the Delay Factor (DF) and the Media Loss Rate (MLR). The Delay Factor gives a hint of the minimum size of the buffer required at the next downstream node. Instead of relying upon MDI Delay Factor (and it’s inherent problems with VBR streams) to estimate buffer requirements, FaultLine directly measures network induced jitter. This measurement, called packet inter-arrival jitter, is computed identically for both CBR and VBR streams and can be reliably used to calculate buffer requirements, the same purpose as the MDI Delay Factor.

In addition to counting lost packets as specified by the MDI Media Loss Rate, FaultLine uses a proprietary, real-time algorithm that examines the context of the lost packets to identify the source (network or encoder).







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