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Video Bitrate, Resolution, and QoE

See the full video from this session, AV1: A Reality Check, on the Streaming Media YouTube channel.

Learn more about emerging codecs and streaming QoE at Streaming Media West 2020!

Read the complete transcript of this clip:

Paul MacDougall: We do a lot of analysis around this particular with regards to our per-title encoding. And I think it's really interesting when we see where resolution can, or does not benefit the perceived visual quality. So, for example, if you look at animation content, you can see much better results by putting your data towards resolution than you would at a higher data rate for a smaller frame size. So we see better-looking video when it's at 1080p at, say, 500 Kbps than when it's, say, 360p at 600 Kbps. Those sharper lines that you get from that higher resolution are going to be much more apparent to users. 

If you have something that has a texture like grass, that texture might not be as easily represented. It might be more accurately represented by resolution, but it might not be as perceptually represented by resolution. If you have a sports player--somebody quickly moving across the scene--you're going to benefit that much more by spending that resolution on that person moving. That's what's going to lead to a better end-user experience.

So I think we really can see that there's definitely not a linear relationship. I had a discussion recently with a customer that was really examining the quality of video. They were using a method that was based on bits per pixel--taking the raster size and how many frames they were using and then dividing the bits used for that to come up with this number. They were using that metric as their way to determine video quality.

But of course that really doesn't give you a good understanding of what the end user is going to see when they're watching on their display. And that's what really matters at the end of the day. That's what the VMAF metric in particular has really been striving towards: simulating what a person sees, how they feel about that video in their home, how that communicates what they're trying to understand for it. It's not just a mathematical formula that might provide some sort of easy-to-understand number that doesn't necessarily really give you a good indication of what you're you're seeing when you're watching that.

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