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30th January 2019, 05:55 | #1402 | Link | |
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30th January 2019, 10:35 | #1403 | Link | |
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One encode, several metrics. Not re-encoding targeted for metrics.
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LAV Filters - open source ffmpeg based media splitter and decoders |
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30th January 2019, 10:42 | #1404 | Link | |
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https://beta.arewecompressedyet.com/...y-525f981376bd |
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30th January 2019, 12:29 | #1405 | Link | |
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The real problem is that VMAF is not that good. It, for example, spectacularly fails with samples that greatly benefit from AQ (yes, I know you already hinted at this).
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30th January 2019, 13:57 | #1406 | Link | ||
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30th January 2019, 17:56 | #1407 | Link | |
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Netflix uses "hVMAF" as official notation in their charts. "h" means "harmonic", which means it uses harmonic means, which bias towards the least favourable. So in your example, the harmonic mean would be 62.66, whereas the average would be 62.86. Neither of these is 65.3. So I'm personally not as concerned about the averaging mechanism aspect of your concern. (In the CLI, use --pool harmonic_mean or something similar, depending on which exact tool you use.) On the other hand, I don't believe that VMAF uses temporal consistency in the reconstruction (the "motion" component is calculated from the source), so that particular concern ("frame throbbing" - i.e. keyframe pulsing or grain/textured-background tearing) I agree with. [edit] Actually, I have to hedge a little here, since I'm not 100% sure VIF (another VMAF component) has a temporal component to it. I don't think it does but I'm not 100% sure. [/edit] Since we're on the subject, here's some more of my personal concerns about VMAF: * it's luma-only; * AQ (x264/5) or SAO (x265) appear to have a negative impact on vmaf score, which is inconsistent with the reported visual results. I do have more detailed thoughts on this but let's leave that for some other time; * the actual MOS/VMAF correlation depends very strongly on the viewing environment and therefore on the used model file, but most poeple simply use the default model without knowing what viewing environment it represents. Just to be clear, I'm not trying to talk badly about VMAF, I think it's a great tool, it's better than the alternatives and it's fantastic that they opensourced the library as well as the models so that we can learn and understand how it works and constructively critique it. Hopefully, over time, that will make it even better, which should be the ultimate goal. Separately, I also do agree with you that in the end, we should probably make a distinction between codecs optimized using VMAF vs. those that did not. This isn't an excuse to suck at writing encoders or to not use VMAF when writing encoders, but at the end of the day, we have to acknowledge that as in any metric, we're assuming a perfect correlation between our metric-of-the-day and the visual experience (or MOS score). That correlation will in practice always be imperfect, and therefore tuning towards/using that metric needs to be done with care and with visual confirmation (otherwise queue up the incoming VMAF artifacts - I wonder what they will look like?). Last edited by Beelzebubu; 30th January 2019 at 22:11. |
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30th January 2019, 21:57 | #1408 | Link |
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@Beelzebubu
What's really funny, Netflix will not be using VMAF on their published AOM content as is. Why? Because of film grain synthesis
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31st January 2019, 06:00 | #1409 | Link | |
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If VMAF is bad at dealing with film grain, they need to address that. The nice thing about VMAF is that it's really a machine learning framework. They can keep on adding new clips and kinds of encodings and training it to rate those. The big expenses is getting the subjective ratings to use as ground-truth data. But VMAF itself can always be as good as the ground truth data from subjective testing. |
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31st January 2019, 06:38 | #1410 | Link | |
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I don't know what Netflix currently does, but if I were them I would filter the grain from the video, run the VMAF-targeting dynamic optimizer to produce the rate controlled stream, and then add the noise parameters back as a final step. |
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31st January 2019, 20:33 | #1413 | Link | |
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1st February 2019, 20:13 | #1414 | Link | ||
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SVT-AV1 encoder!
https://github.com/OpenVisualCloud/SVT-AV1
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1st February 2019, 20:20 | #1416 | Link |
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It should be able to run on any AVX2 CPU.
But the entire series of SVT encoders (SVT-HEVC is also a thing) is designed specifically for a use-case of running them on powerful datacenter systems with loads of memory and CPU cores.
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1st February 2019, 20:47 | #1417 | Link | |
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I don't think there's ever been an encoder that could usefully use anything like 112 cores except via GOP-level parallelism. But hey, it's Intel. I've not been able to find much detailed documentation about the SVT HEVC or AV1 projects. Do they mean "Scalable Video" ala SVC and SHVC with enhancement layers, mainly used in videoconferencing? Or scalable in the sense of scaling with hardware? Leveraging the new low-level encoder SDK from Intel offers some interesting potential for very fast initial estimates for encoding, leaving the CPU to focus more on refinement. There isn't an AV1 encoder in the current Intel CPUs, obviously, but perhaps some VP9 functionality added in Kaby/Coffee Lake can be leveraged. Certainly things like weighted prediction and coarse motion vectors could be reused to some degree. SVT HEVC has a full 8-bit HEVC encoder implementation to leverage in Skylake-S+ and 10-bit in Kaby/Coffee. Unfortunately there aren't any Xeon processors with VP9 encoding yet. The best available is the 8/16 core i9-9900K. I don't see any public roadmap for when AV1 might be added. Ice Lake? I see that has an all new HEVC encoder at least. Although given tape-out schedules and how recent the AV1 bitstream was finalized, a full fixed-function implementation might not be there before Tiger Lake. (all just personal speculation fueled by Wikipedia). I am very curious to see what comes out of the next generation of GPU-assisted software-defined encoding. Having it all on-die instead avoid the PCI bus latency challenges of past GPU+CPU implementations. |
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1st February 2019, 20:50 | #1418 | Link |
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Hardware. Its not producing "scalable video".
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LAV Filters - open source ffmpeg based media splitter and decoders |
2nd February 2019, 00:26 | #1419 | Link |
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No. Intel bought eBrisk (they already owned a good chunk of eBrisk, thanks to the Altera acquisition, because Altera had invested in eBrisk), and then open sourced their HEVC encoder. Then they started focusing on AV1, and now they've open sourced that encoder. The HEVC encoder is fast, but the video quality is not competitive. I'm not sure if it can beat x264 under equal conditions. It certainly can't beat x265 or Beamr 5 under any conditions.
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