Blu-ray Ripper - CUDA vs Software file size difference

gto

I have been using DVDFab for quite some time now and recently got a new computer and was setting up some benchmark test to compare the speed of my old computer to my new. My old computer is an Alienware 17MR3 with an Nvidia 560 graphics card which does not support CUDA processing. My new computer is a MSI GP72 with a Nvidia 1050 graphics card which DVDFab shows does support CUDA processing (I am using driver version 385.41 released on 08/24/2017). I setup to do a Blu-ray rip on each computer with exactly the same settings with the only difference being CUDA enabled on the MSI. The ~2hr move rip was completed in about 20min on the MSI and about 5 hours on the Alienware. (Note that I am ripping using MP4.265 with CRF 30 and re-encoded audio to AC3). Although I was extremely pleased at the increase in speed, I noticed that the file size on the CUDA enabled MSI computer was about 70% bigger than on the Software only Alienware file. I then re-ran the rip on the MSI computer with only Software enabled and got the exact same file size as the Alienware computer that was a Software rip (and about the same time to complete). I did some visual comparisons also, and I cannot tell much difference in the quality of the CUDA vs Software files.

So my question is, why is the file size so much larger for a H.265 rip with CUDA enabled versus doing a software only rip? I have attached my DVDFab log file to this post for review if you need it.

Thanks for any help you can give me.

gto

I ran a similar test using MP4.264 and this time the CUDA file was about 10% smaller than the Software only file. I don't understand why the file sizes are different depending on hardware acceleration or not.

Does anybody have any information on this issue?

Dora

@gto

I have reproduce this issue. I have feedback to our developer.

gto

Is there any update on this issue? I have a Blu-ray collection awaiting a solution...

Dora

@gto
We have a holiday , so it is not fix now.
Please waiting for fix.

Wilson.Wang

From Our Developer,
1. Intel/Nvidia/AMD hardware encode not have same crf as soft.
It is actually CONSTQP, and similary to crf.

2. In DVDFab h264 profile crf default is 20, h265 profile crf default is 26.
If your use crf 18 for h264, you should use 24 for h265 encode.

3. Some video encode gropus often use soft crf 18 VS nvidia constqp 22.
It better to test ripper a chapter to decide which should use 22, 23 or 24.
They all reasonable for balance video quality and size for hevc crf (CONSTQP) encode.

gto

Thanks for your reply! However, I still have a few questions. From some other things I have read (see links below), CRF and CONSTQP are not really the same thing. CRF will vary the encode compression based on the complexity of the scene to give a visual impression of the same rate from complex scenes to simple scenes. The amount of compression is varied and is therefore more efficient use of file size. CONSTQP will use the same compression rate for both complex and simple scenes and will take a larger file size overall as it is less efficient to compress simple scenes.

So in order to use the most efficient compression, I would have to do in software only mode and loose the speed advantage of the CUDA acceleration. Is there any way to do CRF with CUDA acceleration?

See this link below entitled "CRF Guide (Constant Rate Factor in x264 and x265)" by Werner Robitza

Wilson.Wang

Hi gto,

From Our Developer,
Nvidia hardware encode do not support CRF.
Soft CRF more like varies Q , VS , Nvidia const Q.
Soft do much complex, Hardware will be limited by video engine chips.

Wilson