Blog Post by Charlie Kraus
Delivering low latency live streams is essential for live sports, online gaming and just about anyone who wants to offer a great online video experience. In this blog I’ll address innovative ways that Limelight is solving this problem now and will in the near future. To take a close look at the importance here, check out this blog where I discussed the business drivers for complementing live TV sports broadcasts with live streaming, and the challenges presented in delivering live streams with low latency so that viewers can experience the event in near real- time.
Typical latencies delivering HLS or DASH over the internet are in the 30 second to one minute range. This is because of HTTP-based protocols which stream chunks of data. Because each chunk is generated and viewed in real-time, chunk size is a significant part of latency. For example, the default HLS chunk size is 10 seconds, and three chunks are created before delivery begins, leading to a delivery latency of up to 45 seconds when CDN ingesting, transcoding, distance between source and viewer, and delivery are factored in.
An obvious approach to lowering latency is to reduce the chunk size. This is exactly what we have done. To provide deployment flexibility, Limelight offers two small chunk size solutions. The first is Multi-Media device Delivery (MMD) Live small chunk streaming, and is targeted at organizations that want Limelight to handle transcoding. RTMP live streams are ingested and transcoded to HLS or DASH with 1 second size chunks, and delivered to users with total latency of as low as 6 seconds. This latency is adequate for many use cases.
The second solution, Video Acceleration, is a configuration option in the Content Delivery Service which is designed to accelerate the delivery of very small video chunks, and dynamic manifest files (see more about video delivery services here). This capability benefits organizations that do their own transcoding, and deliver HLS and DASH live streams from their own infrastructure that the Limelight CDN uses as origin for cache fill. Because transcoded chunks are ingested, the CDN will zip the chunks across the network to the edge for delivery in milliseconds to the last mile networks. This will reduce live streaming latency down to as low as 3 seconds, a significant improvement over existing HLS and DASH live streaming delivery solutions. There are several successful in-production deployments of both MMD Live small chunk streaming and Video Acceleration that satisfy use case latency requirements.
The industry focus on solutions to replace Adobe’s upcoming end-of-life for Flash for low-latency streaming is a technology called WebRTC (Web Real-time Communication), which is supported by all the popular browsers. Limelight is partnering with Red5 Pro to develop and implement WebRTC-based low-latency live video streaming across our global content delivery network. By integrating WebRTC streaming support into the CDN, content distributors will be able to easily implement scalable live video streaming workflows such as gambling, gaming, and sports broadcasting that require the lowest possible latency. Viewers will finally be able to watch broadcast quality live streaming video as close to real-time as possible. Limelight is active in evaluating this technology, with the promise of providing even lower latency than our current MMD Live small chunk streaming and Video Acceleration. Stay tuned for more information about this exciting development.
Video Acceleration is applicable in these scenarios:
Reduce the latency difference between a TV broadcast and the online stream delivery
Consistent viewing experience across multi-devices for non-simulcast delivery
Scaling the delivery of low-latency live video delivery to large audiences
Ensuring a consistent low latency experience to users across a range of devices
The gambling use case for low latency streaming has two important considerations. The most obvious is to deliver consistent low latency to online players, so they all see the action in near realtime on any device, anywhere they are. For the online casino, if the latency to players is reduced, it speeds play, resulting in more dealing rounds and increased revenue.