AV over IP Bitrate Becomes the Design Variable

Matrox has added a new family to its AV-over-IP line. The Maevex MGX series is described as IPMX-ready, carries USB support, and is offered as single- and dual-channel encoders (MGX E1 and E2) and decoders (MGX D1 and D2). The headline claim is 4K60 distribution at one twentieth the bitrate of virtually all other ProAV codecs, with a default of 50 Mbps that can be tuned. One input can stream simultaneously in IPMX, RTSP, MPEG-TS and SRT; the E2, D1 and D2 add multiview and compositing in 2x1 and 2x2 layouts; HEVC 4:4:4 output is aimed at video wall appliances; and keyboard, mouse and webcam extension travel over the same link.

Engineers should read that claim twice, because bitrate is now the variable that decides the network. At 50 Mbps per stream, a 1 Gbps access port theoretically carries twenty streams and practically carries ten to twelve once headroom, multicast replication and uplink oversubscription are counted. At 8 to 15 Mbps of well-tuned HEVC the same port carries sixty. At the 700 Mbps to 1 Gbps of a lightly compressed codec it carries one, and the design changes from a single switch to 10GbE uplinks, per-flow QoS and a serious multicast plan. The same rack of decoders therefore has three different bills of materials depending on a number that rarely appears in a brochure.

The second reading is about which protocol that number belongs to. Matrox's one-twentieth figure comes from its own IQ mode, which is designed for use between compatible Matrox devices. Over the open protocols - H.264 and H.265 via RTSP, MPEG-TS or SRT - the encoder is subject to ordinary codec efficiency, so a mixed-vendor estate will not see the same result. That is not a criticism; it is the difference between a closed performance mode and an interoperable one, and both are legitimate as long as the specification says which is being quoted. Ask for the bitrate at 4K60 4:4:4 in the protocol the room will actually run, and ask what latency that costs: the vendor quotes as low as one frame in IQ mode, against the tens to hundreds of milliseconds that RTSP-class streaming implies.

Two further details matter at design stage. Carrying USB over the video stream turns the endpoint into a KVM node, which is a decision about input redirection and therefore about security, not convenience. And IPMX with NMOS means discovery and routing are supposed to work across vendors, which only holds if every device on the fabric implements IS-04 and IS-05 at the same version. Amtune's decoder range, hybrid matrix chassis and multi-viewers are specified with locked per-output EDID, so a stream that arrives at 1080p stays at 1080p and a 4K canvas is not quietly renegotiated by the weakest display in the room.