Video: How Netflix Leverages VMAF, Part 1: Codec Comparison
Learn more about VMAF at Streaming Media's next event.
Watch the complete video of this presentation from Streaming Media West, VMAF: The Journey Continues, in the Streaming Media Conference Video Portal.
Read the complete transcript of this clip:
Zhi Li: For codec comparison, here is what we do. If you have three different codecs, we want to evaluate their performance. What we start with is the content. We can now be selecting clips, each one about several seconds or even one minute, and we're going to be collecting thousands of them. For each one, we're going to be performing a trial in coding, trying to sweeping during coding bitrates.
At the same time we're going to collect their quality score, and the quality metric we use in this case is going to be VMAF.
It's similar if you can do that for PSNR, but we trust VMAF more because we believe it's more aligned with human perception. So once we do that we have all those curves. And next step we're going to do a video rate calculation, which is essentially the average percentage differences between those curves. So the average over the entire curve.
By doing that we can build this comparison diagram where it shows how many percentage points one codec performs over the other.
In this particular case we're comparing X.265, X.264, and VPX, VP9 in this case. And those diagrams give us the results of the codec comparison, and we're going to be making decisions based on that.
Most recently, we have introduced a new way of doing codec comparison. Instead of separating different encoding resolutions, we're going to be having everything on the same scale instead of separating them.
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