Worse video quality with GPU acceleration than without ? (MainConcept Codec)

[Norman Black]

This is known. GPU based encoders, thus far, do not have the same encoding quality as purely CPU based encoders. They make compromises in quality for performance. The difference is typically only noticed at low bitrates which is what you are encoding to.

Note that when you select CPU or OpenCL/CUDA in Mainconcept, each one is a completely different encoder with different algorithms.

When it comes to max quality at low bitrates nothing really compares to the x264 encoder.

[Cedric Divang]

Oh noooo 🙁 Thank you very much for your reply Norman. Now I understand why they ask us to choose with of without GPU acceleration in the MainConcept Render Properties :-/ The quality difference is huge !

You said that x264 is the best codec for max quality at low bitrates, but I far as I know, it’s not available in Sony Vegas because of the GPL restrictions. That’s why I use MainConcept which gives me amazing results on Variable Bit Rate mode.

Let’s hope that MainConcept updates his GPU algortyhm but apparently it hasn’t been touched for years since the latest compatible Video card is the ATI Radeon 6970 that came out in … 2011 ! ( See the “Tech Specs” tab here : https://www.mainconcept.com/eu/products/sdks/gpu-acceleration/opencltm-h264avc.html ).

After your message, I did some research and have found that GPU acceleration is actually “incredibly difficult” for video encoding because video encoding is a linear process while GPU relies on parallel processing. A guy from the x264 project says that the only way of making it non linear is by using different algorythms and make significant sacrifies 🙁

Look at this very interesting video : https://www.youtube.com/watch?v=uOOOTqqI18A

[Norman Black]

[Cedric Divang] ”
You said that x264 is the best codec for max quality at low bitrates, but I far as I know, it’s not available in Sony Vegas because of the GPL restrictions”

I render an intermediate format and use Handbrake to use x264 for final low bitrate encodes.

XAVC-S and DNxHD are two formats that work well as an intermediate to Handbrake.

[Dave Haynie]

[Cedric Divang] “The quality difference is huge !”

This does tend to be a low-bitrate thing. And that’s not a shock… it’s pretty difficult to get just the right look at lower bitrates, and I’ll bet that the CPU version is doing things that simply don’t translate well to GPU coding… or are maybe just too complex.

Another thing to realize about MainConcept is that, as Norman mentioned, the GPU coder is a totally different piece of software. Main Concept MPEG and AVC go back decades, but the accelerated encoder was brand new code in Vegas 11, and unfortunately, that’s about the time MainConcept (and parent company DivX) were acquired by Rovio. Nothing much seems to have happened with this CODEC over these last three years. I suspect it’s typical of this… when a company like Rovio acquires a “components” company like DivX, they’re more interested in spending time getting that tech put into their other products than they are worrying about the future of that company’s much smaller market.

Anyway, even the CPU rendering isn’t as good as x264, as Norman mentioned. x264 is an open source project that’s had some clever and very vocal programmers working on it, pushing it harder than I’d guess just about anyone’s ever pushed the H.264/AVC spec. So particularly on low-bitrate stuff, it’s just better. This is the same AVC engine that Google uses for YouTube.

Handbrake is a good open source encoder that uses x264. Though you’ll probably find that just about anything that’s open source and creates H.264 video is doing it with x264. I’m kind of surprised someone like, oh I dunno, Sony, hasn’t incorporated x264 into their products. Sound be possible, even under the GPL, since Sony’s rendering engines are already external modules. And given that Main Concept seems to have given up on improving things.

TMPGenc’s Video Mastering Works also uses x264 as one of several AVC encoding engines (also supports Intel’s, which is tweaked for some x86 chips, and nVidia’s, which of course runs on nVidia GPUs… no OpenCL yet).

I love the integrated encoders. But given the rate at which Sony’s been adapting to new things like GPU acceleration, H.264 improvements, WebM/VP8/VP9, H.265, etc (eg, pretty much not at all), it doesn’t hurt to at least be aware of external encoding options. To use an external encoder, you have to export your complete project, of course, in some intermediate, high-quality format that’s accepted by the encoding program.

Nice video… yeah, that’s the x264 guy… very opinionated, but he’s got the results to back him up. And he does touch on some of the real problems. Obviously, video encoding does benefit from parallelism… that’s what happens in every actual hardware implementation. Of course, the x264 folks will claim they do better encoding than hardware encoders, too (and keep in mind, every hardware encoder is actually a bunch of software, some regular everyday CPU encoding, and a bunch of application-specific hardware). And they might be right.

Good news is that the GPU active in Vegas makes every render faster, simply because it’s applied to plug-ins, compositing, etc. So even if you run CPU-based AVC encoding, you benefit from the GPU (GPU acceleration ON in Vegas, CPU-Only on MainConcept).

-Dave

[Cedric Divang]

Thanks for this very long and interesting post Dave. It was a pleasure to read !

Handbrake seems to be the software most people use to encode in x264. I tried it and it looked pretty complicated (too many parameters to set), not to mention that I’d have to render in Vegas before passing the video to Handbrake. Too much work 😉 I’ll stick with MainConcept for now.

Yes I have GPU enabled in Vegas and disabled on MainConcept 🙂

[Cedric Divang]

Hi again norman, I’ve followed your advice and am now exporting the project to .MXF (blazing fast because it doesn’t need recompression !!!) before passing it to handbrake. I have a little question : A .sfl file is created by SVP along with the .mxf file. What is the .sfl ? Can I safely delete it ? Is there a way to prevent SVP from creating this file ? Thanks for your help 🙂

BTW you were right, the x264 render is better than MainConcept (which still gets very good results for me) and looks somewhat faster with the settings I use. I hope the x264 developers find a way to implement GPU acceleration (apparently it’s just used for cropping or scaling down for now) because their codec is awesome and the devs look talented 😀

[Cedric Divang]

nvm i’ve found the answer on the web, the .sfl can be safely deleted

[Gabe Carter]

I was also having some serious problems getting decent render quality out of Vegas using the MainConcept encoder. I went deep down the rabbit hole of rendering out uncompressed and passing into Handbrake for the final render, until I discovered that Vegas CAN render H.264 or x264 with a simple codec pack. For some reason I had just assumed there was some reason it couldn’t do this, or else why wouldn’t Sony just included it?

Anyways, I grabbed the x264vfw coded pack here:
https://sourceforge.net/projects/x264vfw/files/

That gives me the H264 codec option in Vegas under the “Video for Windows (.avi)” if you customize any template you’ll see the new codec option. It renders WAY better than MainConcept or SonyAVC, at about half the file size. To my eyes, it’s as good as Handbrake after getting my settings right.

[Jim Prisby]

Gabe,
Following your instructions…After installing the x264vfw coded pack I chose to render my Sony Vegas 13 HD project to “Video for Windows (.avi)” and selected HD 1080P-60i and changed the video format from Sony YUV codec to the x264 codec. But then there is a configure button there to configure it. What settings should I change in the configuration? I’m rendering this to go into DVD Architect and then burn it to a Blu-ray disk.

Thanks,
Jim

Intel 2.67GHz Core2 Quad CPU.
8 GB RAM
NVIDIA GForce GTX 570 superclocked
Windows 7 64bit

[Wayne Waag]

For the easiest way of encoding with Handbrake from Vegas, do this.

https://www.vegasvideo.de/vegas-2-handbrake-en

Frameserve–No intermediates. As many would say, it works a treat. Try it.

wwaag