Changing the Equation for Live Streaming and ABR Video Quality


On the surface, it seems counter-intuitive: Save bandwidth while improving video quality? It reminds me of something my grandfather used to say: “You can’t swim and be dry at the same time, can you?”

The riddle that is quantity vs. quality goes way back. Think back to the VCR. They used to have a physical setting on the machine, to select between how much you taped, vs. how good the recording was. Most people set theirs on “extended play,” for six hours of recordings, vs. “best quality,” which pinched that back to two hours. They picked quantity, over quality. Because you couldn’t have both at the same time.

Fast-forward (pun intended) to now, and the industrial shift to cloud-based video streaming. For wired and mobile service providers, video is the heaviest thing they carry — and they carry a lot of it. Last year, video represented roughly three quarters of what moved over the Internet, according to our latest Visual Networking Index, and is expected to go to 82% in three years.

Delivering it better than the next guy, without breaking the bandwidth bank, is, for service providers, a relentless and delicate interplay between compression, and picture quality. After all, bandwidth is neither infinite nor free — and providing a superlative video experience is an important competitive differentiator. Compress it too much, mess with the experience. Back off too much, send the bandwidth costs through the roof.

At this week’s Consumer Electronics Show, we’re releasing a white paper with the freakishly spicy title “Video Quality for Live Adaptive Bit-Rate Streaming: Achieving Consistency and Efficiency.” It’s about the latest developments in video encoding (and, in particular, our Virtual DCM), and how an innovation called “smart rate control” can both save bandwidth — and improve picture quality.

Here’s the crux of it: Today’s “constant bit rate,” or “CBR” encoders, work by “right-sizing” a video stream for the screen that displays it and the network that delivers it. Sending an HD-sized stream to a screen the size of a smart phone is transmission overkill. A whole lot of bits fall onto the floor, metaphorically speaking, unneeded and unused. In telecom parlance, that screen was massively over-provisioned.

What’s smart about smart rate control is it’s the ability to be “content aware.” If you’re an encoder, and your job is to compress a picture, you’re going to have a much easier time with a “talking head” than with a World Cup game. And the less complex the video content is, the more it can be compressed, without disaffecting the quality.

But how are we to trust a piece of machinery — in software — to make subjective observations about video quality? Because smart rate control comes with a vigorously tested metric: stream video quality, or SVQ. Its purpose is to continuously steer the encoder toward a constant quality, for each encoded profile (which is to say, chunk of video.) In essence, the SVQ gives a ranking, 1-low to 10-high, on each encoded frame, or segment, of video.

And by “vigorously tested,” I mean that the SVQ metric was tested against 10 commonly used objective measures in the media industry, using databases well known in the research community. It came through with — well — flying colors (no more puns. I promise!)

When put into action, our encoders outfitted with smart rate control and SVQ both optimizes bandwidth and reduces operating costs. This is true for wired and mobile networks. How much bandwidth? In our tests and customer trials, the bit rate savings across sports, movies and news averaged 36%.

Those bit rate savings have an immediate and beneficial effect on operating costs. Check out the examples in the paper, which offers a brief financial model on both wired and mobile networks.

And one more thing: the application of smart rate control is ideal for live video streaming. Why? Because the SVQ is a very lightweight and computationally efficient metric, thereby limiting the overhead in live streams.

Bottom line is this: You still can’t swim and stay dry at the same time, but, as it turns out, you actually can trick out your video encoder to conserve bandwidth, while improving picture quality.

There’s a ton more detail in the paper, and if you’re like me, you’re facing some fairly significant airplane time over the next week or so…happy reading!


Author: Yoav Schreiber
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