In-room AV distribution has the advantage of aiming for highest resolution quality but typically without concerns for low-cost cabling. An in-room solution is point-to-point over comparably short cable distances. As such the benchmark for an in-room solution tends to be 4k60, 4:4:4 for video. By contrast, a multi-room AV distribution solution is based on AV-over-IP (AVoIP) tools in order to facilitate scalable distribution with minimal cable costs. In order to meet the same image benchmarks of 4k60, 4:4:4 data compression or large network bandwidth are necessary.
The differences between multi-room and in-room approaches are in the cabling and infrastructure, but is comes down to the CODECs to deal with those differences. AVoIP networks that can provide 4k60 need more than 10GB bandwidth to run uncompressed. Even with light compression the bandwidth requirements well exceed 1GB. While 10GB paths are often available, to truly have the freedom to distribute AV to essentially any user, the CODECs must be optimized for 1GB networks.
“Multi-room matrixing can be accomplished with HDBase-T type systems (for reduced cost) for local routing of all video signaling,” says Robert Bagnull, senior associate with Cerami Associates
. But there are limitations in how big the matrix can be and the I/O count will determine the need to go to a non-centralized network approach.”
Multi-room AVoIP tends to require devices from the same manufacturer to get signals onto and off of the network. There are few technologies for converting AV to Ethernet-based packets and back again. As such, hardware manufacturers have developed proprietary methods for doing so which then precludes interoperability with regards to the devices at the on-ramps and off-ramps. As Bagnull explained, “The idea of decentralized AV switching or routing is not a new one, but with the advent of increased visual performance and resolution standards, bandwidth has become more critical requiring either more coding and decoding (adding latency) or subsampling (reduction in quality). Network speeds have increased, but not to the point to allow 4k60 4:4:4 to be transported via IP without specialized hardware.”
One of the only non-propriety solutions on the market is Audio Video Bridging/Time Sensitive Networking, or AVB/TSN. This is an IEEE standard for audio and video to be packetized for Ethernet and delivered with the necessary time synchronization and bandwidth reservation required for low latency and reliability. AVB/TSN does require that the switches also be equipped with chipsets that are capable of handling the synchronization and bandwidth reservation, but a number of major switch manufacturers are providing hardware that is certified by AVnu, a consortium overseeing interoperability with AVB/TSN.
In-room AV and multi-room AV have different requirements and must be approached differently. While it is possible to use the same technology for both, one will come with larger compromises than the other. A network-based approach for an in-room solution will likely require 10GB network bandwidth to meet the same benchmarks as point-to-point connections. The distribution requirements of a multi-room AV system would require the affordability of network-based cabling, but 10GB networks become prohibitively expensive.AV Technology magazine's technical advisor, Justin O'Connor, has spent nearly 20 years as a product manager, bringing many hit products to the professional AV industry. He earned his Bachelor’s degree in Music Engineering Technology from the Frost School of Music at The University of Miami. Follow him at @JOCAudioPro. Subscribe today for The Agile Control Room newsletter sponsored by RGB Spectrum (distributed twice per month, every other Tuesday).