IP

Video: Case Study: Dropbox HQ ST 2110

Posted on by Russell Trafford-Jones

Dropbox is embedded in many production workflows – official and otherwise – so it’s a beautiful symmetry that they’re using Broadcast’s latest technology, SMPTE ST 2110, within their own headquarters. Dropbox have AV throughout their building and a desire to create professional video from anywhere. This desire was a driving factor in an IP-based production facility as, to allow mobile production platforms to move from room to room with only a single cable needed to connect to the wall and into the production infrastructure.

David Carroll’s integration company delivered this project and joins Wes Simpson to discuss this case-study with colleague Kevin Gross. David explains that they delivered fibre to seventy locations throughout the building making most places into potential production locations.

Being an IT company at heart, the ST 2110 network was built to perform in the traditional way, but with connections into the corporate network which many broadcasters wouldn’t allow. ST 2110 works best with two separate networks, often called Red and Blue, both delivering the same video. This uses ST 2022-7 to seamlessly failover if one network loses a packet or even if it stops working all together. This is the technique used with dropbox, although there these networks are connected together so are not one hundred per cent isolated. This link, however, has the benefit of allowing PTP traffic between the two networks.

PTP topology typically sees two grandmasters in the facility. It makes sense to connect one to the red network, the other to the blue. In order to have proper redundancy, though, there should really be a path from both grandmasters to both networks. This is usually done with a specially-configured ‘PTP only’ link between the two. In this case, there are other reasons for a wider link between networks which also serves as the PTP link. Another element of PTP topology is acknowledging the need for two PTP domains. A PTP domain allows two PTP systems to operate on the same network but without interfering with one another. Dante requires PTP version 1 whereas 2110, and most other things, require v2. Although this is in the process of improving, the typical way to solve this now is to run the two separately and block v1 from areas of the network in which it’s not needed.

PTP disruptions can also happen with multicast packet loss. If packets are lost at the wrong time, a grandmaster election can happen. Finally, on PTP, they also saw the benefits of using boundary clock switches to isolate the grandmasters. These grandmasters have to send out the time eight times a second. Each end-device then replies to ascertain the propagation delay. Dealing with every single device can overwhelm grandmasters, so boundary clock switches can be very helpful. On a four-core Arista, David and Kevin found that one core would be used dealing with the PTP requests.

A more extensive write-up of the project can be found here from David Carroll

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Speakers

Kevin Gross Kevin Gross
Media Network Consultant
AVA Networks
David Carroll David Carroll
President,
David Carroll Associates, Inc.
Wes Simpson Wes Simpson
Owner, LearnIPVideo.com

Video: Reliable and Uncompressed Video on AWS

Posted on by Russell Trafford-Jones

Uncompressed video in the cloud is an answer to the dreams that many people are yet to have, but the early adopters of cloud workflows, those that are really embedding the cloud into their production and playout efforts are already asking for it. AWS have developed a way of delivering this between computers within their infrastructure and have invited a vendor to explain how they are able to get this high-bandwidth content in and out.

On The Broadcast Knowledge we don’t normally feature such vendor-specific talks, but AWS is usually the sole exception to the rule as what’s done in AWS is typically highly informative to many other cloud providers. In this case, AWS is first to the market with an in-prem, high-bitrate video transfer technology which is in itself highly interesting.

LTN’s Alan Young is first to speak, telling us about the traditional broadcast workflows of broadcasters giving the example of a stadium working into the broadcaster’s building which then sends out the transmission feeds by satellite or dedicated links to the transmission and streaming systems which are often located elsewhere. LTN feel this robs the broadcaster of flexibility and cost savings from lower-cost internet links. The hybrid that he sees working in medium-term is feeding the cloud directly from the broadcaster. This allows production workflows to take place in the cloud. After this has happened, the video can either come back to the broadcaster before on-pass to transmission or go directly to one or more of the transmission systems. Alan’s view is the interconnecting network between the broadcaster and the cloud needs to be reliable, high quality, low-latency and able to handle any bandwidth of signal – even uncompressed.

Once in the cloud, AWS Cloud Digital Interface (CDI) is what allows video to travel reliably from one computer to another. Andy Kane explains what the drivers were to create this product. With the mantra that ‘gigabits are the new megabits’, they looked at how they could move high-bandwidth signals around AWS reliably with the aim of abstracting the difficulty of infrastructure away from the workflow. The driver for uncompressed in the cloud is reducing re-encoding stages since each of them hits latency hard and, for professional workflows, we’re trying to keep latency as close to zero as possible. By creating a default interface, the hope is that inter-vendor working through a CDI interface will help interoperability. LTN estimate their network latency to be around 200ms which is already a fifth of a second, so much more latency on top of that is going to creep up to a second quite easily.

David Griggs explains some of the technical detail of CDI. For instance, it has the ability to send data of any format be that raw packetised video, audio, ancillary data or compressed data using UDP, multicast between EC2 instances within a placement group. With a target latency of less than one frame, it’s been tested up to UHD 60fps and is based on the Elastic Fabric Adapter which is a free option for EC2 instances and uses kernel bypass techniques to speed up and better control network transfers. CPU use scales linearly so where 1080p60 takes 20% of a CPU, UHD would take 80%. Each stream is expected to have its own CPU.

The video ends with Alan looking at the future where all broadcast functionality can be done in the cloud. For him, it’s an all-virtual future powered by the increasingly accessible high-bandwidth internet connectivity coming in a less than the cost of bespoke, direct links. David Griggs adds that this is changing the financing model moving from a continuing effort to maximise utilisation of purchased assets, to a pay as you go model using just the tools you need for each production.

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Download the slides
Please note, if you follow the direct link the video featured in this article is the seventh on the linked page.

Speakers

David Griggs David Griggs
Senior Product Manager,
AWS
Andy Kane Andy Kane
Principal Business Development Manager,
AWS
Alan Young Alan Young
CTO and Head of Strategy,
LTN Global

Video: IP-based Networks for UHD and HDR Video

Posted on by Russell Trafford-Jones

If you get given a video signal, would you know what type it was? Life used to be simple, an SD signal would decode in a waveform monitor and you’d see which type it was. Now, with UHD and HDR, this isn’t all the information you need. Arguably this gets easier with IP and is possibly one of the few things that does. This video from AIMS helps to clear up why IP’s the best choice for UHD and HDR.

John Mailhot from Imagine Communications joins Wes Simpson from LearnIPVideo.com to introduce us to the difficulties wrangling with UHD and HDR video. Reflecting on the continued improvement of in-home displays’ ability to show brighter and better pictures as well as the broadcast cameras’ ability to capture much more dynamic range, John’s work at Imagine is focussed on helping broadcasters ensure their infrastructure can enable these high dynamic range experiences. Streaming services have a slightly easier time delivering HDR to end-users as they are in complete control of the distribution chain whereas often in broadcast, particularly with affiliates, there are many points in the chain which need to be HDR/UHD capable.

John starts by looking at how UHD was implemented in the early stages. UHD, being twice the horizontal and twice the vertical resolution of HD is usually seen as 4xHD, but, importantly, John points out that this is true for resolution but, as most HD is 1080i, it also represents a move to 1080p, 3Gbps signals. John’s point is that this is a strain on the infrastructure which was not necessarily tested for initially. Given the UHD signal, initially, was carried by four cables, there is now 4 times the chance of a signal impairment due to cabling.

Square Division Multiplexing (SQD) is the ‘most obvious’ way to carry UHD signals with existing HD infrastructure. The picture is simply cut into four quarters and each quarter is sent down one cable. The benefit here is that it’s easy to see which order the cables need to be connected to the equipment. The downsides included a frame-buffer delay (half a frame) each time the signal was received, difficulties preventing drift of quadrants if they were treated differently by the infrastructure (i.e. there was a non-synced hand-off). One important problem is that there is no way to know an HD feed is from a UHD set or just a lone 3G signal.

2SI, two-sample interleave, was another method of splitting up the signal which was standardised by SMPTE. This worked by taking a pair of samples and sending them down cable 1, then the next pair down cable 2, the pair of samples under the first pair went down cable 3 then the pair under 2 went down 4. This had the happy benefit that each cable held a complete picture, albeit very crudely downsampled. However, for monitoring applications, this is a benefit as you can DA one feed and send this to a monitor. Well, that would have been possible except for the problem that each signal had to maintain 400ns timing with the others which meant DAs often broke the timing budget if they reclocked. It did, however, remove the half-field latency burden which SQD carries. The main confounding factor in this mechanism is that looking at the video from any cable on a monitor isn’t enough to understand which of the four feeds you are looking at. Mis-cabling equipment leads to subtle visual errors which are hard to spot and hard to correct.

Enter the VPID, the Video Payload ID. SD SDI didn’t require this, HD often had it, but for UHD it became essential. SMPTE ST 425-5:2019 is the latest document explaining payload ID for UHD. As it’s version five, you should be aware that older equipment may not parse the information in the correct way a) as a bug and b) due to using an old standard. The VPID carries information such as interlaced/progressive, aspect ratio, transfer characteristics (HLG, SDR etc.), frame rate etc. John talks through some of the common mismatches in interpretation and implementation of VPID.

12G is the obvious baseband solution to the four-wires problem of UHD. Nowadays the cost of a 12G transceiver is only slightly more than 3G ones, therefore 12G is a very reasonable solution for many. It does require careful cabling to ensure the cable is in good condition and not too long. For OB trucks and small projects, 12G can work well. For larger installations, optical connections are needed, one signal per fibre.

The move to IP initially went to SMPTE ST 2022-6, which is a mapping of SDI onto IP. This meant it was still quite restrictive as we were still living within the SDI-described world. 12G was difficult to do. Getting four IP streams correctly aligned, and all switched on time, was also impractical. For UHD, therefore SMPTE ST 2110 is the natural home. 2110 can support 32K, so UHD fits in well. ST 2110-22 allows use of JPEG XS so if the 9-11Gbps bitrate of UHDp50/60 is too much it can be squeezed down to 1.5Gbps with almost no latency. Being carried as a single video flow removes any switch timing problems and as 2110 doesn’t use VPID, there is much more flexibility to fully describe the signal allowing future growth. We don’t know what’s to come, but if it’s different shapes of video rater, new colour spaces or extensions needed for IPMX, these are possible.

John finishes his conversation with Wes mentioning two big benefits of moving to IT-based infrastructure. One is the ability to use the free Wireshark or EBU List tools to analyse video. Whilst there are still good reasons to buy test equipment, the fact that many checks can be done without expensive equipment like waveform monitors is good news. The second big benefit is that whilst these standards were being made, the available network infrastructure has moved from 25 to 100 to 400Gbps links with 800Gbps coming in the next year or two. None of these changes has required any change in the standards, unlike with SDI where improvements in signal required improvements in baseband. Rather, the industry is able to take advantage of this new infrastructure with no effort on our part to develop it or modify the standards.

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Speakers

John Mailhot John Mailhot
Systems Architect, IP Convergence,
Imagine Communications
Wes Simpson Wes Simpson
RIST AG Co-Chair, VSF
President & Founder, LearnIPvideo.com

Video: Line by Line Processing of Video on IT Hardware

Posted on by Russell Trafford-Jones

If the tyranny of frame buffers is let to continue, line-latency I/O is rendered impossible without increasing frame-rate to 60fps or, preferably, beyond. In SDI, hardware was able to process video line-by-line. Now, with uncompressed SDI, is the same possible with IT hardware?

Kieran Kunhya from Open Broadcast Systems explains how he has been able to develop line-latency video I/O with SMPTE 2110, how he’s coupled that with low-latency AVC and HEVC encoding and the challenges his company has had to overcome.

The commercial drivers are fairly well known for reducing the latency. Firstly, for standard 1080i50, typically treated as 25fps, if you have a single frame buffer, you are treated to a 40ms delay. If you need multiple buffers for a workflow, this soon stacks up so whatever the latency of your codec – uncompressed or JPEG XS, for example – the latency will be far above it. In today’s covid world, companies are looking for cutting the latency so people can work remotely. This has only intensified the interest that was already there for the purposes of remote production (REMIs) in having low-latency feeds. In the Covid world, low latency allows full engagement in conversations which is vital for news anchors to conduct interviews as well as they would in person.

IP, itself, has come into its own during recent times where there has been no-one around to move an SDI cable, being able to log in and scale up, or down, SMPTE ST 2110 infrastructure remotely is a major benefit. IT equipment has been shown to be fairly resilient to supply chain disruption during the pandemic, says Kieran, due to the industry being larger and being used to scaling up.

Kieran’s approach to receiving ST 2110 deals in chunks of 5 to 10 lines. This gives you time to process the last few lines whilst you are waiting for the next to arrive. This processing can be de-encapsulation, processing the pixel values to translate to another format or to modify the values to key on graphics.

As the world is focussed on delivering in and out of unusual and residential places, low-bitrate is the name of the game. So Kieran looks at low-latency HEVC/AVC encoding as part of an example workflow which takes in ST 2110 video at the broadcaster and encodes to MPEG to deliver to the home. In the home, the video is likely to be decoded natively on a computer, but Kieran shows an SDI card which can be used to deliver in traditional baseband if necessary.

Kieran talks about the dos and don’ts of encoding and decoding with AVC and HEVC with low latency targetting an end-to-end budget of 100ms. The name of the game is to avoid waiting for whole frames, so refreshing the screen with I-frame information in small slices, is one way of keeping the decoder supplied with fresh information without having to take the full-frame hit of 40ms (for 1080i50). Audio is best sent uncompressed to ensure its latency is lower than that of the video.

Decoding requires carefully handling the slice boundaries, ensuring deblocking i used so there are no artefacts seen. Compressed video is often not PTP locked which does mean that delivery into most ST 2110 infrastructures requires frame synchronising and resampling audio.

Kieran foresees increasing use of 2110 to MPEG Transport Stream back to 2110 workflows during the pandemic and finishes by discussing the tradeoffs in delivering during Covid.

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Speaker

Kieran Kunhya Kieran Kunhya
CEO & Founder, Open Broadcast Systems