I recently got it into my head to compare the various popular video codecs in an effort to better understand how av1 works and looks compared to x264 and x265. I also had ideas of using a intel video card to compress a home video security setup, and what levels of compression I would need to get good results.
The Setup
I used the 4k 6.3gb blender project, tears of steel as a source. I downscaled the video to 1080p using all three codecs, and then attempted to compare the results using various crf levels.
To compare results I used imgsli, FFMetrics, and my own picture viewer to try and see what the differences are.
The Results
| crf | av1 KB | x265 KB | x264 KB |
|---|---|---|---|
| 18 | 419,261 | 632,079 | 685,217 – x246 visually lossless |
| 21 | 352,337 | 390,358 – x265 visually lossless | 411,439 |
| 24 | 301,517 – av1 VAMF visually lossless | 250,426 | 263,524 – x264 good enough |
| 27 | 245,685 | 165,079 – x265 good enough | 176,919 |
| 30 | 205,008 | 110,062 | 122,458 |
| 33 | 168,192 | 73,528 | 86,899 |
| 36 | 139,379 – av1 My visually lossless | 48,516 | 63,214 |
| 39 | 116,096 | 31,670 | 47,161 |
| 42 | 97,365 – av1 my good enough | 20,636 | 35,801 |
| 45 | 81,805 | 13,598 | 27,484 |
| 48 | 69,044 | 9,726 | 20,823 |
| 51 | 58,316 | 8,586 – worst possible | 16,120 – worst possible |
| 54 | 48,681 | - | - |
| 57 | 39,113 | - | - |
| 60 | 29,062 | - | - |
| 63 | 16,533 – worst possible | - | - |
I go into more detail with the hows and whys of my choices, in my journal-style blog post, as well as how i came to these conclusions, But in essence, if you want to lose practically no visual information, crf24 through 36 for av1, crf 21 for x265, and crf 18 for x264 will do the job.
If you are low on space, using my ‘good enough’ choices will get you practically the same visual results while using less space, depending on the codec.
You might want to use a code block instead of bullet points for your table, the way you presented it is unreadable but I found the info on your blog page.
One of my criteria for video formats is the portability. Like sometimes I might watch something through a web browser which natively supports x264. Yeah x265 provides better compression, and AV1 certainly looks interesting, but they both require the addition of codecs on most of my viewing devices and in some cases that’s not possible.
For most cases I’ve found that CRF25 with x264 works reasonably well. I tend to download 720p videos to watch on our 1080p TV and don’t notice the difference except in very minor situations like rapid motion on a solid-color background (usually only seen on movie studio logo screens). Any sort of animated shows can go even lower without noticeable degradation.
I did try to format the table here better. I used code blocks the first time, and it ended up being even uglier. After about four edit attempts i kinda just gave up. Tables don’t seem to exist as far as I can tell either.
Your experience with x264 just about matches up with mine. As long as I don’t pixel peep, crf 24 does a pretty great job of conveying the information. It also does a pretty great job of working with just about everything compatibility-wise. I don’t expect it to go away any time soon specifically because of that.
AV1 is super neat in that we can buy hardware accelerated encoding for it for really cheap using the Intel Arc video cards, and can be decoded by their latest CPU generation. It makes for a great choice for something like security camera footage where playback compatibility is good enough (you can play it in a modern pc), hardware encoding works with a 200$ card, and you save a lot of money using the video card instead of buying extra storage space.
Tables do exist ! | Tables | do | exist | ! | |--------|----|-------|---|Stolen. Thank you.
with a 200$ card, and you save a lot of money using the video card instead of buying extra storage space.
With $200, you could buy ~12TB worth of HDD(s) instead. You’d need >36TB of video for that to make financial sense and you’d always lose quality.
Additionally, you’d have to factor in the power it needs to transcode but, with HW accel, it’s not quite as much as with CPUs.
Sure, but that is a choice that couldn’t be made without first checking how much space is saved by switching codecs. This helps with making that decision, but i’m well aware it is only part of the information needed.
Oh the data is absolutely fine and helpful; I only take issue with the conclusion ;)
I would like to have seen more data on that table. The time it took to run each video compression… the final bitrate of each stream. Besides that, very interesting results.
The “av1” numbers, which codec is that? There are many av1 encoders and even for Intel HW accel, there are at least two.
It’s
svt-av1, as can be seen from theffmpegcommand in the article.From my blogpost, i’m using the following command to encode the video;
ffmpeg -i source.2160p.mkv -map 0:v:0 -map -0:a -map -0:s -map_metadata -1 -c:v libsvtav1 -preset 3 -vf scale=w=1920:-2 -crf 23 dest.1080p.av1.mkvThat is not representative of what you’d get with an Intel card then. While they implement the same standard (AV1), they’re entirely different encoders with entirely different image quality characteristics.
How does that work? Aren’t two encoders of the same format supposed to produce the same output for the same input and configuration using some given algorithm? Otherwise I’d consider them different formats/codecs… 🤷♂️ Maybe that’s wrong of me?
The issue is, you can optimize a software encoders continually, you can use tricks for better quality etc.
A hardware encoder is just that - hardware. As soon as it’s burned to the silicon, you’re not making any (at least substantial) changes to it. You might also be limited by what you can actually do directly in hardware without using too much die space.
Tldr.: no, you won’t get the same result
Tldr.: no, you won’t get the same result
What I’m saying is, shouldn’t you?
What you describe is true for many file formats, but for most lossy compression systems the “standard” basically only strictly explains how to decode the data and any encoder that produces output that successfully decodes that way is fine.
And the standard defines a collection of “tools” that the encoders can use and how exactly to use, combine and tweak those tools is up to the encoder.
And over time new/better combinations of these tools are found for specific scenarios. That’s how different encoders of the same codec can produce very different output.
As a simple example, almost all video codecs by default describe each frame relative to the previous one (I.e. it describes which parts moved and what new content appeared). There is of course also the option to send a completely new frame, which usually takes up more space. But when one scene cuts to another, then sending a new frame can be much better. A “bad” codec might not have “new scene” detection and still try to “explain the difference” to the previous scene, which can easily take up more space than just sending the entire new frame.
the “standard” basically only strictly explains how to decode the data and any encoder that produces output that successfully decodes that way is fine
Ah, okay, this explains the whole aspect of it then, for me. :-) If this is how a certain format is described, then it makes sense that encoders can produce different data, which then will be decoded as different output as well, all while all parties are compliant with the specification. That makes much more sense. Thanks for taking the time to explain everything, including I-frames and P-frames! ;-)
Doesn’t
libsvtav1do the same on all platforms since it’s CPU-based? At least that’s the exact encoder OP specifiedYes, yes it will. (Well, at least it should. If it doesn’t, that’s a bug.)
The problem here is that the premise of this post is evaluating buying a GPU with AV1 encoder in order to transcode a media library. Any GPU-based AV1 encoder will produce very different results than svt-av1, likely much worse results that is.
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Can you explain what you mean by “visually lossless”? Is this a purely subjective classification, or is there a specific definition or benchmark you used?
Visually lossless means I couldn’t tell an image difference even when pixel peeping with imgsli. Good enough means I couldn’t tell a difference in video, but could occasionally see a compression artifact in imgsli.
The VMAF results are purely objective measurements. You can read more about it here; https://en.wikipedia.org/wiki/Video_Multimethod_Assessment_Fusion
I’ve also gone down that rabbit hole and found Vivictpp pretty good. It allows you to play two videos so you can swipe between them like imgsli you mentioned.
There’s a whole range measurements trying to approximate quality differences between a video source and encode. PSNR, SSIM, VMAF, MS-SSIM
All of them with some strong areas and tricks you can use to cheat them.Just buy bigger disks 🫢
Larger file size means significantly larger cost when you’re working with lots of data… especially when transferring data over the internet
