Posts about video quality metrics
BD-Rate computations are a valuable metric when comparing theoretical codec performance. But just because they prove that HEVC is 40% more efficient than H.264 doesn’t mean that you’ll save 40% of your bandwidth if you switch to HEVC. This 6-minute video lesson explains why and suggests a better alternative for estimating real-world benefits. I include…
These are the most popular video quality metrics-related articles on the Streaming Learning Center over 2019-2020. I hope you find this list of resources useful. Installing and Using Netflix VMAF-Master – I call it VMAF-Master because that’s the name of the ZIP file you download from Github here, though the Windows executable that I used and…
This week’s lesson is an updated lesson for my course, Computing and Using Video Quality Metrics: A Course for Encoding Professionals. The agenda is shown in the YouTube frame. The lesson starts with an overview of rate-distortion curves and BD-Rate functions, what they are, and how you create them. Then I get into a pet…
While standards-based video codecs like H.264 and HEVC tend to dominate, standards-based video quality metrics have never risen to the same usage or attention level. With two innovative and highly accurate metrics now available from the ITU-T, this may change in the near term. Briefly, these models are: ITU-T Rec. P.1203, which calculates the quality…
TL/DR: Netflix updates VMAF to include a new model that reverses out the effects of techniques like sharpening, contrasting, and histogram equalization. As I reported in VMAF is Hackable: What Now?, you can increase VMAF scores via simple image enhancement techniques like sharpening, contrasting, and histogram equalization, which, when applied inappropriately, may not actually improve…
Happy to report a five-star review for my course, Computing and Using Video Quality Metrics: A Course for Encoding Professionals. As far as I know, it’s the only course available that teaches how to compute and use metrics like VMAF, PSNR, SSIMPLUS, and SSIM, including how to create rate-distortion curves and BD-Rate comparisons. The review…
There are many quality metrics that use a variety of scoring mechanisms. One of the most frequently used metrics for subjective testing is called Mean Opinion Score, or MOS. The MOS rating is on a scale from 1-5 as shown below (from Wikipedia). You can use a variety of techniques to compute MOS, but typically…
I just finished one consulting project that involved testing 22 clips with three codecs to produce nine rate-distortion charts per clip (1080p, 720p, 480p for VMAF, SSIM, and PSNR) and am working another with 35 clips with 4 RD charts each with two encoding modes. So efficient chart creation in Excel is now a huge…
If you’re comparing codecs with video quality metrics, you should consider tuning for that metric. However, x264 and x265 don’t have a VMAF tuning option. According to my analysis, it appears that tuning for PSNR is the best option and one you should strongly consider. When working with VP9, there’s an additional complication; tuning for…
Producing the chart above involved encoding 35 files using 5 different presets and then recording start and stop times. Since the files were about 20-seconds long, seconds were important. I’m sure a smarter compressionist than I could write a Python script to harvest the start and stop times but I do it by hand, which…