Choosing Streaming Codecs for QoE and Perceptual Quality
The cynics in the streaming pundit class often liked to say that transcoding video for streaming delivery is about taking good video and making it worse. The challenge, of course, is to make whatever quality degradation results from compression as imperceptible as possible. Choosing the right codecs for live or on-demand streaming requires balancing multiple considerations, from player and playback compatibility to conserving bit and preserving quality.
In this clip from Streaming Media Connect, perceptual quality expert and IMAX CPO Abdul Rehman discusses the key decisions that go into choosing a streaming codec when trying to deliver the best QoE to end viewers.
Knobs, Dials, and the Role of QoE and Perceptual Quality in Live and VOD
Recognizing the need to examine the differences between codecs and how they impact QoE down the line, Padem Media Group President Allan McLennan asks Rehman, "At IMAX, with the sheer size of the files that you're having to compress and put out into the market, how do you go about doing that, and is that different between your live and on-demand distribution decisions?"
"Obviously, I think that's where QoE and perceptual quality play a major role," Rehman replies. Encoding decisions, he says, are "where it goes back to knobs and dials. Within an encoder or within a codec, you have lots of different knobs and dials, right? First you need to come up with a subset of the knobs that the player and the rest of the ecosystem can support at the end of the day. And after that, you need to build a platform that would tell you the impact of those decisions on quality and cost, so you can make more informed decisions."
Balancing those priorities, he says, means determining "what's good enough"--or how much want to exceed that baseline standard--and with VisionScience, IMAX has devised a way of measuring that, both for live and on-demand. "It's a binary decision, first up, that you want to operate at 'good enough' or you want to do better than that."
Another issue that routinely comes up in QoE discussions about streaming platform performance, Rehman says, is, "Where do you sit in comparison to other streaming platforms? A is better than B is better than C. Again, I think there are technologies out there that you can absolutely do that. I have written reports on how Streaming Platform 1 performs versus 2 versus 3 on latency, on quality, and all those things. This is not rocket science anymore. It's all possible. It becomes a chicken-or-egg problem. If you don't have the data then you can't make the business case and you're not going to make the business case because you don't have the data. So we don't want to get into that situation."
Alternatives to Changing Codecs
Even though changing codecs is one way to address QoE issues, Rehman says it's easier said than done; comparing it to "open-heart surgery," he insists that there are easier ways. "Yes, you can go and pick one codec versus another one, but you really need to be prepared for the downstream effect of that," he says. "That's a huge investment, and you need to justify it from a cost perspective."
A comparatively cost-effective approach, he says, "is picking an encoder. So you do that, and then relatively easier than that is to pick a rate control--a knob that's available statically on premises" with which you can experiment. "Even better that," he continues, "you can dynamic optimization and not change anything. We do the full range of that when we deliver live content to giant 80-foot screens across the world. We have done events in Korea, we have done events in Taiwan recently. We have done sports events in the U.S. where we literally have passionate fans screaming. We talk about what's good enough on that screen, and we deliver that while taking advantage of all of these levels and measuring it as scientists as we have trained to do for decades to be able to deliver at that level of quality expectation.
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