V14 weird frozen pixels in main concept AVC export with GPU on

Mindmatter wrote on 3/14/2018, 11:20 AM

Hi all,

I ran into another GPU acceleration artifact issue with V14. I had shot a 1080p / 25 interview with my A7S and the shogun Flame on DNXHD 220. All was well, I didn't even bother to transcode as it was a short, uncomplicated timeline thing with just a few animated texts.

Preview was accordingly slow and sluggish, but workable in preview/full mode.

I rendered to mainconcept AVC, set to average 16 and max 20mbs. The result, with GPU on, was appalling. Every split second the head wasn^t moving, the codec chose to freeze and even somewhat defocus parts of her face / skin as well as some inanimate objects in the frame. Usual first culprit suspition: turn GPU off - and it was much better, but still present.

Next render with Sony AVC set to 16mbs, and all was OK again.

Why is it that the GPU activity messes the rendered files up so badly? It's not the first time, last issue on a complex project was a total mashup of the compositing elements, which were randomly displaced across the frame. Is it the DNX codec? is it GPU interference in general? Why was Sony's AVC flawless and the other one not?

If you know something I don't, please share..

thanks!

Comments

fifonik wrote on 3/14/2018, 5:04 PM

Welcome to the club.

The Mainconcept encoder was changed in VP12 and since then it produces something like you describing (if I understand you correctly). Magix AVC encoder in VP15 behaves the same way. I do not thing this is a bug in encoder, I think it is something like the encoder's configuration that can only be altered by developers.

There is no workaround with Mainconcept/Magix AVC (that I know) other than to increase bitrate so the issue will not be visible much. At this moment I'm slowly working on demo project that will display the issue and allow others to analyze results. Then i'm going to send it to Magix (I reported the bug to Sony long time ago, bug nothing was fixed, may be Magix will be able to change this). The project is almost ready, I'm working on detailed description (English is my second language so it is not very easy to to explain everything in writing).

Most people do not care about the quality issue, they mostly care about encoding speed.

The only good thing -- the issue usually extremely visible only under some circumstances when a lot of details in background (trees, grass) and not too many details on main object (face).

P.S. To keep quality I'm rendering with x264 encoder through frameserver.