Video: Do You Really Need Low-Latency Streaming?
While low latency is a goal for all live streaming applications, commonly associated with reliability and a better user experience, reducing latency also increases the expense of delivering large-scale streams. In this excerpt from his presentation at Streaming Media East 2017, Wowza VP of Product and User Experience Mike Talvensaari argues that low latency isn't always worth it, and that you should prioritize it only in certain use cases.
Watch Mike Talvensaari's complete presentation, Achieving Low-Latency Streaming at Scale, on the Streaming Media Conference Video Portal.
Mike Talvensaari: We hear terms like low latency, ultra-low latency, real time. What do we really mean when we talk about these things? So I'm going to start at the left combination for the latencies for HLS and DASH. These are upwards of 45 seconds, 30-45 seconds depending in you're going through a CDN. And this is for one way streams to large audiences. I have to have massive scale, people want to see it in HD, or 4K. And so I can deal with latency there. Reduced latency is kind of 5 to 20 seconds. 2-18 seconds. And this would be live streaming of news, sports, and content for OTT providers.
Low latency. 5-7 seconds is typical latency for HD cable TV. And so we call low latency anything faster than that. And this is for live streams, game streaming, E-sports--sometimes you want to try to match that 5-second delay if you're streaming television content. So it matches up with what people are seeing if they're watching on TV. You want to be shouting “Goal!” at the same time as your neighbor if you're watching a sporting event.
And the near-real time is sub-1 second. So this would be for real-time communications, conferencing, any sort of telepresence, real-time device control. I'm controlling a PTZ camera, I want to hit the button and see it pan right immediately. So that's near-real time. That's some definitions.
People think they need really low latency streaming all the time but they don't necessarily need it. So in designing your system, if you want low latency, it's just going to cost more. You're going to have to buy more expensive devices. You're going to have to have more servers. Higher quality, higher bandwidth. But you often don't need lower latency. A 30-second delay is not often a problem.
So latency doesn't actually matter. So really think about, do I need low latency? Does my use case need low latency? If I'm streaming high school sports, does it really matter if grandma in California sees it 30 seconds delayed or not? Probably doesn't matter.
HTTP streaming, which is the most popular format for streaming now, intentionally introduces latency for improved reliability. So Apple HLS and MPEG-DASH, both by default out of the box require three chunks to be loaded. The chunks are 10 seconds, that gives you a huge buffer of time for network hiccups. Buffering has been greatly reduced over the years due to things ... like this. And so, reliability has improved with some of these things.
For some live streams latency is critical. If you're doing rea- time communication, it's critical. Anything over a second is painful. If you're doing online gaming, any sort of remote control devices ... gambling, auctions, latency is critical for certain use cases.
Sometimes low latency is critical, but in other streaming applications it's not worth prioritizing, Wowza Senior Solutions Engineer Tim Dougherty argues in this clip from Streaming Media West 2018.
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