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AV Over IP – A Primer

AVoverIP

AV Over IP is the term for technology that delivers audio visual content over Ethernet. The term also implies that content traditionally sent or switched over analog or digital switching now employs IP packets and standard Ethernet switches between the source and destination.

There are two basic AVoIP applications, Distribution and Presentation.

Distributed IP Delivery

  • Content is distributed over a large area
  • Endpoints described as encoders and decoders
  • Usually a high ratio of decoders to encoders
  • Streams are highly compressed to save network bandwidth
  • Half- to 1-second latency is acceptable, depending on application
  • Streams can provide captioning data and audio sync

Distributed content is sent over large areas, including nationwide through Netflix or over a single site from cable channels, modulated over RF coax, or via an IP network. Due the larger scale of distribution, streams should be as small as possible, able to carry ADA captioning, and don’t require instant switching for viewing. The standard format for this application is MPEG, usually MPEG2 for off-air TV and in-house RF channels, and H.264 for commercial and consumer IP-based TV.

MPEG is designed for maximum compression – H.264 can easily compress a 3Gbps (bits per second) 1080p video to a 15 mbps stream, a 200:1 ratio, and consumer streams are compressed far more. The secret sauce is called the GOP, the Group of Pictures, and only the first frame is an actual image. MPEG compresses the first frame into an image similar to a JPEG. The encoder then captures a few more frames and notes objects that move or change color, and saves just that data. This is called inter-frame encoding, as the encoder is continually cross-referencing frames. When a decoder changes a stream, it has to capture the first several frames in the next GOP and rebuild the video back to its original content. This deconstruction/reconstruction process takes time, creating about a half- to one-second delay. That’s why you experience a pause when changing MPEG channels.

Presentation IP Delivery

  • Displayed in a defined area
  • Endpoints described as transmitters and receivers 
  • Simpler to define and expand input/output configurations
  • Large streams require a dedicated IP network
  • Instant switching, about 2-4 frames
  • Streams composed of images and audio tracks, no captioning data

When a system is delivering a live presentation or event, the content on the video screens must to be in sync with what’s on the stage or podium, and cameras need to be changed instantly. Visible latency is disconcerting to the presenter and audience. This is the traditional application for AV switching systems.

The new counterpart to AV Switching is routing content over an IP network. Instead of a central switch with multi-port input and output cards, designers can define any number of individual transmitters and receivers, routed through a standard Ethernet switch.  Video frames are converted to stream packets using Motion JPEG 2000, typically compressed to 3:1 to 20:1 ratios. As the stream consists of individual images, switching is fast, with little latency. 

However, latency is a bit looser than AV’s vertical-interval switching. IP guarantees delivery, but there is no central clock to lock down timing, so there are network variables that could affect latency. As with AV switching extensive scaling at the input and output points can affect latency as well. As there is not sync data as there is in MPEG, audio could be behind – or ahead of the video, especially if the video is highly compressed and scaled and the audio just passed through. I would imagine some IP systems offer settings to minimize audio timing issues. 

What is the Effect of 4K video on commerical IP distribution systems?

For commercial systems, 4K is more of a marketing pitch than a reality. Current room and screen designs can’t take advantage of 4K, and very little content will be 4K for some time. It just isn’t needed. 

MPEG distribution technology is typically limited to 1080p. However, H.264 does support 4K and “zero latency“. For the present, 4K codecs such as HEVC (H.265) and VP9/AV1 aren’t usable for commercial applications.

 

Testing Multicasting with WireShark

wireshark

Wireshark is a free IP testing tool from Wireshark.org. Download and install the app if you don’t have it already. There’s a great deal of information you can glean from a Wireshark network scan, but the following will focus on verifying IGMP multicasting setup and operation. I’m assuming you already know how to use VLC.

  • Launch Wireshark
  • Launch VLC and enter the same network stream used for the VLC test, or get ready to select channels from a QIP-D decoder
  • Click the Shark Fin icon at the top left to begin a network scan
  • Enter “igmp” in the line under the icons and click Enter on your keyboard.
  • Click Play in the VLC window, or turn on the QIP-D and select a channel when the unit has spooled up
  • Stop VLC or change channels on the QIP-D
  • This will show IGMP activity. The scan above shows:
    • One or more General Membership queries from network switch 192.168.0.6
    • A request from the VLC (the PC 192.168.0.191) to join IGMP group 239.27.0.101 and later on, 239.27.0.102.
    • Membership Leave queries streams for 101 and 102
    • VLC sends a Leave response
  • This means that the encoders, decoders and switches are operating correctly.
  • You can stop the scan and save the results, if desired.

Expressing a Vision: Willow Creek

viewfrombooth

During my time at AMX, I was the ghost-writer for many magazine articles. As many industry publishers would not accept articles from vendors, I created stories for our integrators, who didn’t have a professional writing staff. However, I was able to submit a story under my own name for Technologies for Worship magazine called Expressing a Vision: Willow Creek, which covered the technology, but focused on leadership. I’ve been a worship sound tech for a few decades, and how the church met the vision, rather than the stuff, was impressive to me. You can click on the link above to read the full story, but my conclusion was this:

In the end, the Willow Creek story really isn’t about technology; it’s about how technology, architecture, and people can work together to meet a common vision.

  • Define the Vision. A new project begins with a reason. Leadership should clearly define measurable goals, preferably in terms of people, not things.
  • Earn and Accept Authority. Willow Creek’s team had earned leadership’s trust, having the clear responsibility to conform the design to the stated objectives.
  • Find Wisdom. In addition to in-house experts, consultants and integrators are important resources for any successful project.
  • Plan. The project team should be given the time to preset a well-reasoned plan and budget to leadership. Technology often rewards those who wait.
  • Keep in the Loop. Keep the team together and communicating throughout the project to ensure what is designed well is installed correctly.
  • Mobilize the Membership. You’ll receive a lot less resistance from the congregation if they are partners in the solution.

Finally, speaking for all the sound, video, lighting and staging staff serving in worship spaces around the world – thanks guys, for getting it right.

 

Bridging the 10G/1G Divide in IP Video Switching

1G-10G Bridge

IP Switching Tech Simplified

Up to now, AV over IP solutions are divided into two groups – 10G or 1G networks. While both market their solutions differently, they use the same technology. Under the hood, all use Motion JPEG 2000 or a variation, developed years ago, initially for archiving video. Files can be compressed up to 3:1 without losing original quality, and the video stream is composed of individual compressed frames, simplifying video editing and switching. When you go to a digital movie theater (and almost all are now), you’re watching a 4K Motion JPEG 2000 video.

AV vendors quickly moved to JPEG 2000 for IP switching for the same reasons – excellent compression, switching, and 4-8K capacity-and the codec is free. While many vendors have tweaked and renamed the codec to make it proprietary, the functionality is the same.

  • 10G systems use “mathematically lossless” 3:1 compression to reduce a 16G 4K video to less than 6G. That’s great, but 10G switching can’t run well over Category cable, requiring fiber for all connections.
  • 1G systems use 20:1 “visually lossless” compression, resulting in an 800 Mbps stream that can use standard 1G switches and Cat 5e/6 cable. It’s a good tradeoff – 4K quality is still great and more functional, as most commercial systems will be routing 1080p streams, anyhow.

The key point is that the divide between 10G and 1G systems is purely arbitrary – the only difference is compression.

2.5G/5G Networks over Cat 5e/6 Cable

The division between 10G and 1G systems will be narrowed with the advent of 2.5G/5G Ethernet. While 10G is useful for connecting switches, it’s bust for wiring PCs. Sites already have millions of miles of 5e/6 Cat cable installed; there’s no way they will replace wiring with Cat 6a/7 or fiber.

2.5G/5G technology isn’t a new or proposed standard, it’s always been a part of 10G technology. In basic terms, 10G is a large checkerboard of data, while 2.5/5G is a smaller section in the center. That smaller section enables the transmission of 2 to 5 times more information over Cat 5e/6 cable than 1G Ethernet.

What’s new is the advent of multi-gigabit 1/2.5/5/10G IP switches and IP ports than can portion out the right speed for the application – typically 10G between switches, 2.5G to Cat 5e feeds, and 5G through Cat 6 wiring. It’s a great solution, adding new power to existing networks just by upgrading switches instead of installing new copper or fiber.

While a growing number of multi-speed switches are available, PCs, laptops, IoT devices and AV over IP gear are supplied with 1G ports. That will change over time as IT admins gradually adopt the new capability.

However, change may be quicker in AV over IP solutions, as suppliers can go beyond the 1G barrier, delivering 4K video at two to four times less compression over standard 5e/6 Category cable – just by upgrading their Ethernet ports. That’s a game-changer!