ffdshow's DXVA video decoder problem

[Music Fan]

That's what I feared.
For DXVA in avisynth with a Nvidia card, shouldn't we use DGDecNV ?

[Asmodian]

Well I would suggest DGDecNV for gpu decoding on an Nvidia card but it would CUDA decoding, not DXVA.

I would bet a bit of money Nev will not implement anything for DXVA on XP or anything special for XP.. XP really is too old at this point (typing on an XP machine at work atm ).

[Music Fan]

It's old but still used a lot. Is it so hard to code for XP compared to Win7 ?
I hope ffdshow's team will do something in the kind of LAV DXVA copyback for XP.

What's the difference between decoding by CUDA and DXVA ?

[Guest]

Strictly speaking, it is CUVID, not CUDA, that performs the decoding for DGDecNV. CUVID is an API to the PureVideo engine.

[clsid]

CUVID works on XP.

Don't expect any improvements to ffdshow. Its project has been pretty much dead for more than a year.

[Music Fan]

Didn't know that, bad news.

CUVID works on XP

Ok but I need DXVA copyback for my ATI.

[clsid]

Copy-back is a feature of DXVA2, which requires Vista or above. It is not a limitation that is specific to the implementation in LAV.

[Music Fan]

Ok, so there is no hope for my configuration.

[Music Fan]

Hi,
is it still impossible to use DXVA decoding with Avisynth on Windows XP ?
As I said above a few months ago, I'd like to use my ATI's GPU with avisynth, which can be done with LAV but not on XP. And as clsid said, Copy-back is a feature of DXVA2, which requires Vista or above.
Thus I wonder if another way than copyback to use DXVA decoding with Avisynth exists or would be technically possible.

[nevcairiel]

DXVA1, which is used on Windows XP, is extremely limited. You won't be able to use it with AviSynth. You should switch to a newer OS if thats a requirement for you.

[Music Fan]

Ok, but I'd like to understand why MPC-HC (and maybe other players) can use DXVA on XP and Avisynth can't.
Is it because players do real time and Avisynth needs a kind of buffer memory (to store decoded frames) to allow slower than real time rendering, which wouldn't be possible with DXVA1 ?

[nevcairiel]

All you can do with DXVA1 is decode the video and then immediately show it on the screen (for playback). AviSynth needs to process the image to do its job, thats just not possible with DXVA1.
You don't need to fully understand it to accept that its impossible.

[Music Fan]

I understand, you answered my question. I guess that's what is called copy-back and that it's impossible with DXVA1.
CUDA looks different on that point because it can be used with Avisynth on XP, thanks to DGDecNV.

[Music Fan]

Hi,
I do have Windows 7 64 now but I still can't make LAV work with Avisynth ;

Originally Posted by detmek

Yes, with DirectShowSource() or DSS2() (if you have Haali Splitter) and LAV Video decoder set to DXVA-Copyback.

I don't have Haali Splitter, is it also needed for DirectShowSource() (which I tried but DXVA-Copyback stays inactive) or only for DSS2() ?
I got picture (I opened my script in Virtual Dub) but as I see "inactive" below DXVA-Copyback in LAV's video decoder window, I guess the video is decoded by another filter.

[clsid]

You must access the settings of LAV by clicking on its tray icon to see the correct decoder state. Clicking on the Start menu shortcut loads another instance, which shows <inactive> because that instance of the filter is in fact not active!

[Music Fan]

I don't see its tray icon
But I believe LAV's copyback is not used because my CPU is around 45 % when I play this script while it's only around 3% when I play the TS file (the same than the one in my script) in MPC-HC (which use GPU).

[clsid]

Win7DSFilterTweaker can help you set LAV Video as preferred decoder.

[Music Fan]

Thanks, I will try this.

[Music Fan]

It works now when I play an Avisynth script opened in Virtual Dub (I see active for dxva2cb when I click on LAV's tray icon), but the CPU usage for a 1080p24 h264 video is around 20 %, which is quiet high for DXVA.
With MPC-HC 32 bit (installed on Win 7 pro 64) set also on LAV DXVA copyback playing the same video (without Avisynth), CPU usage is around 13 %.
I'm astonished by this difference because my script is very simple, one line (it was just for the test) ;
directshowsource(F:\my video.mp4")
I guess it means Avisynth needs more resources than MPC-HC because the decoder is exactly the same.
With Microsoft decoder instead of LAV's (chosen with Win7DSFilterTweaker), CPU usage is around 40 % (twice dxva2cb).

Before to install MPC-HC 32 bit (for compatibility with Avisynth 32 bit), I installed MPC-HC 64 bit and the CPU usage was around only 3 % with 1080p videos ! I used the default setting (DXVA activated but I don't know if LAV was used).
I had the same result (3 %) with MPC-HC 32 bit on XP 32 bit.
Does it mean that MPC-HC 32 bit works better on 32 bit OS than on 64 bit OS ?