Low-Latency Streaming

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A few weeks ago, I was watching a Champion’s League soccer game. Once again, my viewing experience was badly spoiled by the neighbors shouting around 40 seconds before I actually saw the goal on my screen.

How come this is still happening in 2021? Many technology companies have announced solutions for OTT low-latency streaming over the past few years, but as a viewer, I still face the same issue.

Let’s find the culprit…

There are several time-related parameters that can have an impact on the user experience, so it can be confusing. These include latency, zapping time, start-up time, and more. Let’s start with a definition of latency: latency is the time it takes for the video content to go from the camera to your screen.

This delay is due to the different stages required to process and deliver video content. It is usually in the range of 5 to 10 seconds for broadcast and IPTV but 30 to 40 seconds for OTT multi-screen video delivery. This is why, when watching soccer on my tablet, I see the goal 30 seconds after my neighbors, who watch the same game on a DTT TV set.

In-depth analysis shows that most latency comes from buffering in the player application in the end-user device (about 15 to 20 sec) and the HLS or DASH packaging operation (about 5 to 10 seconds). The encoder (about 1 to 2 seconds) and the CDN (several hundred ms) seem to have a lower impact. But as we will see, driving down OTT latency requires an end-to-end strategy, as every stage has its role to play.

… and make sure this will never happen again!

Video encoding (or video compression) is the initial processing stage to consider and obviously allow some latency optimization. However, this optimization needs to ensure that we keep a pristine video quality, even with 4K HDR content. This is critical for the viewing experience in sports streaming, as detailed in this blog post.

Then, standard OTT protocols (HLS/DASH) recommend that video content be packaged into segments lasting from 2 to 10 seconds, and delivered (to the CDN). This packaging operation can start only when the segment is fully available. On top of that, the player on the device needs to buffer at least one full segment before it can start playing the content.

The CMAF media file container format opened the possibility of dividing such segments into shorter chunks of a few hundred ms. This was first applied to the Low-Latency DASH (LL DASH) protocol. Lately, it has also been applied to Low-Latency HLS (LL HLS). Each chunk can then be delivered after a few hundred ms (instead of 2 to 10 seconds) and the player can start displaying the content with only a few chunks’ buffering, drastically reducing latency (check out our Low Latency webinar for more details).

Also, to speed up video delivery over the CDN, other features were included in the standards recommendation – for instance Chunk Transfer Encoding for LL DASH and Http 2 support for LL-HLS.

Finally, and as briefly introduced above, the player is also a critical component to reach the 5-to-10-second-latency goal, so it is important to make sure it fully supports LL-HLS and/or LL-DASH and the associated requirements.

Get ready for the FIFA World Cup next year with ATEME

The good news is that at ATEME, we have been working very hard to ensure that the major OTT platforms are able to offer low-latency OTT streaming at scale, in both DASH and HLS protocols, to all their subscribers.

The latest proof of this was our ability to deliver the world’s first Just-In-Time packaging origin/packager able to manage both Low-Latency DASH and Low-Latency HLS (with subtitles and encryption) in what has become a reference architecture for OTT delivery.

In parallel, we have also worked on other optimizations such as Byterange packaging to reduce the number of requests needed by the player and further improve the user experience while minimizing the network load (more details also available in our Low Latency webinar).

The outcome is that today, you can reach the promised 5-to-7-second latency by relying on ATEME’s end-to-end OTT video delivery. And while some of our customers had already deployed such services in LL DASH, they can now add Low Latency HLS to provide a perfect user experience to everyone.

Their objective? To be ready for the World Cup next year. So if you also want your viewers to enjoy broadcast-level latency, get in touch with us to find out how we can help!