A dirty secret of the live streaming industry is that a “live” broadcast isn’t truly live. In reality, most live video broadcasts today have a latency between 5 and 30 seconds—and sometimes longer. Lowering glass-to-glass latency is a key performance improvement indicator for many live broadcasters today. Low latency streaming is especially important in certain industries. These include sports, video game streaming, breaking news, etc, where delay is a major quality issue for viewers.
Thankfully, low latency streaming technology has made major strides over the last few years. New delivery protocols and streaming solutions for optimizing existing standards like HLS are pushing latency lower and lower. And more improvements are coming soon. In this blog article, we’ll update our readers on the latest trends in low latency streaming technologies.
The Latency Triangle
Before we dive in, let’s first consider the trade-offs involved in low latency streaming. Dacast partner THEOplayer describes latency using a triangle analogy. One point of the triangle represents low latency streaming. The second corner of the triangle represents high quality. This category includes higher resolutions, higher frame rates, and avoiding buffering. Lastly, the third corner relates to scalability for large audiences.
Through this analogy, THEOplayer makes the point that maximizing any one of these attributes may require sacrificing one (or more) of the others. Extremely low latency live streaming is currently possible. However, it’s only possible via protocols like WebRTC, which aren’t optimized for one-to-many live streaming. In other words, scalability is compromised. Similarly, maximizing video quality often means boosting buffer sizes and bandwidth requirements. This introduces higher latency issues and a greater load on live streaming CDNs.
Overall, the latency triangle helps us to understand low latency streaming challenges that broadcasters, CDN providers, and video hosting platforms are working to solve.
How AWS Tests Latency at the CDN Level
Do you know what the latency is on your live streams? If not, you should find out.
Amazon’s AWS cloud computing and CDN service, another Dacast partner, provides recommendations for reducing latency. Their first step: measure latency. In other words, you can’t improve latency without a clearly defined baseline.
Next, place a second device next to the device running the clapperboard app. Now you can access the test stream on this device. Once the stream is playing, take a photo of the two screens. The difference between the time-codes on the two devices will give you a precise video latency number.
In addition, AWS is working to reduce video latency in various ways. Today, the standard latency is now less than 10 seconds. Moreover, they offer stable 4-second latency for businesses that require it.
The SRT Alliance and New Low Latency Streaming Protocols
SRT is an open-source video transport protocol and technology stack. It can help to optimize streaming performance across unreliable, variable speed networks. SRT has built-in secure delivery and easy firewall traversal, bringing high-quality live video even over the worst networks.
The SRT protocol is a significantly modified version of the UDT (UDP-based Data Transfer) protocol, which centers on high-speed data transfer rather than live streaming. SRT works via an error correction mechanism to ensure regular frame rates across variable network conditions. Click here for a detailed technical overview of SRT.
The use of SRT is increasing at the broadcaster level, but it’s still a new and evolving technology. Dacast is a member of the SRT alliance, and we strive to keep our readers and our services up-to-date as SRT matures.
5G Networks and Low Latency Streaming
One upcoming boon for low latency streaming involves the rise of 5G cellular networks. A few select cities in the U.S. have already installed 5G networks. Even more exciting for broadcasters, experts predict that networks will explode in 2020 and 2021. Streamingmedia.com predicts that the most noticeable gains will occur for video streaming: “5G will also be a boon to live sports and event streaming, IHS predicts. When having low latency is critical, 5G’s gains will become most apparent.”
Minimizing Latency Using HLS
In 2020, HLS is by far the dominant streaming video format. But unlike other protocols, HLS does not inherently minimize latency. In fact, early versions of the HLS protocol had a latency of 30 seconds or more. However, that number is changing. In 2019, Apple introduced a new version of HLS that makes serious improvements to low latency performance.
Of course, there are more improvements to come in the HLS streaming protocol. According to Pieter-Jan Speelmans, CTO at THEOPlayer, test latencies have dropped down into the 1-second range. This has required some fiddling with the HLS protocol, but it has been effective. However, these latencies are currently impractical at scale, so stay tuned for updates later this year.
Dacast’s Low Latency Streaming Solution
Here at Dacast, we launched our low latency HLS solution (“HLS Direct”) in 2018. It currently features average latencies of roughly 8 seconds. HLS Direct is available to Dacast users on Premium plans and above.
Dacast’s low latency video streaming support is accompanied by a huge extra. We offer a FREE software encoder for HLS ingests live streaming to all our users. This is an industry first and a major advantage of the Dacast video streaming platform. Other HLS-ingest encoders cost a great deal of money.
Our HLS encoder is based on OBS Studio. OBS software is compatible with Windows and Mac and includes a wide range of mixing and production tools. In addition, it supports a wide variety of plugins, scripts, and custom themes that are available for OBS. There is no better option available today for HLS ingest low latency video streaming.
The Future of Low Latency Streaming: CMAF and Beyond
Looking ahead, the next step in low latency streaming is the chunked Common Media Application Format (CMAF) approach. CMAF allows users to achieve stable 3 to 7-second latency without disrupting the current distribution infrastructure that is so common. It does so by combining features of the HLS and DASH protocols into a single optimized format.
CMAF currently uses HTTP 1.1. However, upcoming new protocols like HTTP/2.0 and QUIC will integrate UDP technology into CMAF, further reducing latency. It’s possible this could reduce latency into the 1-second range. In 2020, we expect CMAF to reach a vastly expanded audience. According to one survey, 47 percent of broadcasters plan to use HTTP Low Latency technologies (which include low-latency CMAF for DASH and Apple Low-Latency HLS) to deliver sub-three-second streams at scale in the near future.
As this post highlights, low latency streaming solutions represent a rapidly advancing technology. Protocols are evolving quickly as low latency is an increasing priority for many broadcasters. With that trend in mind, we hope you now better understand what’s ahead in the world of low latency streaming.
If you’re looking for a low latency video platform today, we can help! Our HLS Direct service produces stable sub-10-second latency for large, scalable audiences. We offer a white-label video hosting and live streaming platform, as well as a 30-day free trial (no credit card required)! That way, you can test out all the features before committing to our OVP. Click the button below to sign up today.
Do you have further questions or comments about low latency streaming? If so, we’d love to hear from you in the comment section below. And if you need professional assistance with your low latency setup, feel free to contact us.
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