Video Quality Metrics (VQM) Discussion

[CrypticSignal]

👋 Welcome!

You can use this section to:

• Ask any questions that you may have about VQM.
• Suggest ideas/improvements to VQM.

[brandonnys]

There appear to be two dependencies not listed in the documentation:
NumPY
PrettyTables

[InB4DevOps]

Please see requirements.txt.
Both numpy and prettytables are included in the file.

[derekguenther]

I understand Handbrake is basically just a front-end for ffmpeg, and it allows some "additional parameters" to be fed in. For example, "rc-lookahead=10:bframes=5:ref=6:subme=7:aq-mode=3" is recommended for Blu-rays by this website, but since they're recommending the NVENC encoder which is fast but doesn't compress it well I'm not sure how much I trust their recommendation. I'm looking for the best compression while still having high quality, to minimize the space taken in long-term storage.

1. How can I feed these parameters into VQM?
2. Any thoughts on adding some testing around these parameters, similar to CRF?
3. Do you happen to have any recommendations on these parameters for both Blu-ray and DVD?

Fantastic work, this was really helpful for me to decide how I should start encoding a bunch of my media. Thank you very much!

Also, like brandonnys, I missed the "Requirements" section. I was looking for installation instructions and just went for it when I didn't find a section titled that. The info was there, and it's on us that we both missed it, but maybe it's worth a small change to the page to make it more clear?

[CrypticSignal]

"rc-lookahead=10:bframes=5:ref=6:subme=7:aq-mode=3" is recommended for Blu-rays by this website, but since they're recommending the NVENC encoder which is fast but doesn't compress it well I'm not sure how much I trust their recommendation.

The only reason they recommend NVENC is because of the greater encoding speed, the website you linked acknowledges that it is not as efficient: "This also comes with a tradeoff, as it’s not as efficient at reducing the file size as a CPU conversion does."

So personally I wouldn't use the NVENC recommendation as a basis to discredit the additional parameters they suggested. With that being said, I've never used such parameters myself, nor is video encoding something that I do often, so I cannot comment on whether these additional parameters are good.

How can I feed these parameters into VQM?

Currently this is not possible, but this should be pretty simple to implement and therefore I will likely add this functionality to VQM. I won't give an ETA, because since working full time, I have less free time. But I will let you know when the ability to specify -x264opts has been implemented.

Do you happen to have any recommendations on these parameters for both Blu-ray and DVD?

Unfortunately no. Personally if I want to transcode a video file I use CRF (labelled as Constant Quality in Handbrake) to target a particular quality level without messing around with such parameters. You would think that the developers of x264 have optimised parameters such as rc-lookahead etc for each quality level without having to override the values of these parameters, but what do I know, I'm certainly not an expert on x264 encoder settings.

Fantastic work, this was really helpful for me to decide how I should start encoding a bunch of my media. Thank you very much!

You're welcome! It's nice to hear that you found VQM helpful 🙂

Also, like brandonnys, I missed the "Requirements" section. I was looking for installation instructions and just went for it when I didn't find a section titled that. The info was there, and it's on us that we both missed it, but maybe it's worth a small change to the page to make it more clear?

I added a Table of Contents near the top of the README so users can see the available sections (one of them being Requirements) easily. I'm not sure what else could be done, nor do I feel like the requirements are hard to find as there's a dedicated section in the table of contents.

[derekguenther]

"rc-lookahead=10:bframes=5:ref=6:subme=7:aq-mode=3" is recommended for Blu-rays by this website, but since they're recommending the NVENC encoder which is fast but doesn't compress it well I'm not sure how much I trust their recommendation.

The only reason they recommend NVENC is because of the greater encoding speed, the website you linked acknowledges that it is not as efficient: "This also comes with a tradeoff, as it’s not as efficient at reducing the file size as a CPU conversion does."

So personally I wouldn't use the NVENC recommendation as a basis to discredit the additional parameters they suggested. With that being said, I've never used such parameters myself, nor is video encoding something that I do often, so I cannot comment on whether these additional parameters are good.

That's fair, but since they recommend higher up to use NVENC without mentioning the tradeoff (you have to read the whole page, and thank you for doing so!) it's a bit of a concern for anyone whose goals are different than theirs (not just quality, but quality and low file size). Similarly, they also eventually mention that you have to have a higher CRF with the NVENC codec to get similar quality, but you have to read the entire page to get that. It's not that they don't know what they are talking about, but that their approach to the whole thing seems very unscientific, specific to their own use case, and not very clear, which is why I say that I question their recommendations. The scientific approach with VQM, while not perfect (because video quality is unfortunately subjective) means that their single recommendations become suspect. I've been using VQM to identify when my own perception of a video is good/bad and identifying at which analyzed numbers I am happy, which is very useful.

How can I feed these parameters into VQM?

Currently this is not possible, but this should be pretty simple to implement and therefore I will likely add this functionality to VQM. I won't give an ETA, because since working full time, I have less free time. But I will let you know when the ability to specify -x264opts has been implemented.

Thank you! The only other similar question I have is whether some of the encoder tune profiles for x264 (such as Animation) would also be accessible, but I don't know if that's necessary - if you have the time, looking at what's available in Handbrake and adding them would be nice, but it also adds complexity and requires your time, and I certainly don't want you to try to spend overly much time opening up the options for just me. On the other hand, I do have some programming experience, so maybe I could contribute? I am not experienced with GitHub however.

Do you happen to have any recommendations on these parameters for both Blu-ray and DVD?

Unfortunately no. Personally if I want to transcode a video file I use CRF (labelled as Constant Quality in Handbrake) to target a particular quality level without messing around with such parameters. You would think that the developers of x264 have optimised parameters such as rc-lookahead etc for each quality level without having to override the values of these parameters, but what do I know, I'm certainly not an expert on x264 encoder settings.

I'd like to think that, yes, but there's a reason folks on the internet have found these options. For example, by specifying these do I lower the min or standard deviation on a show? If my file size is larger for a particular CRF, but I can lower the CRF because the metrics are better, I believe I would be happier - but I do probably need to analyze with VQM a handful of action movies, sitcoms, animation shows, etc. so that I can come up with an encoder profile I am happy with for each style of show. I'm willing to put the work in for myself, it just depends on what VQM can offer me (which, again, is not your problem - you can only give me what you have time available to give!).

Fantastic work, this was really helpful for me to decide how I should start encoding a bunch of my media. Thank you very much!

You're welcome! It's nice to hear that you found VQM helpful 🙂

I really do! This is excellent.

Also, like brandonnys, I missed the "Requirements" section. I was looking for installation instructions and just went for it when I didn't find a section titled that. The info was there, and it's on us that we both missed it, but maybe it's worth a small change to the page to make it more clear?

I added a Table of Contents near the top of the README so users can see the available sections (one of them being Requirements) easily. I'm not sure what else could be done, nor do I feel like the requirements are hard to find as there's a dedicated section in the table of contents.

Just a thought, why not an "Installation" section detailing what you need to do? Instead of saying "Requirements: Python" why not telling the user where to get Python? The change is helpful, though, thank you.

Also, I put together some basic Windows batch files for adding the ffmpeg location to path just for VQM, rather than adding it to the permanent path. I could try to help out on the project by adding it, though I don't know how. I'm new to using GitHub for serious things. If adding some of these parameters is just a matter of modifying the Python files I could potentially do that too, I just haven't had time/energy to look yet, let me know.