[winswitch] NVENC and xpra

Antoine Martin antoine at nagafix.co.uk
Wed Dec 11 04:33:07 GMT 2013

On 11/12/13 06:18, ... wrote:
> Hello,
> I had some questions about NVENC.  Sorry if this information is somewhere
> already and I didn't find it.
I assume you've already read:
> Can xpra use a kepler enabled nvidia card to both render graphics (hardware
> accelerated) and h264 encode them before shipping them off to another
> display across the network?
According to Nvidia:
"NVIDIA's latest generation of GPUs based on the Kepler architecture,
contain a 
hardware-based H.264 video encoder (henceforth referred to as NVENC). "
So, assuming that this is a pro card or that you found a license key
(...), yes you can use NVENC with such cards.
This answers the second half your question.

As for the "render graphics hardware accelerated", it is a little bit
more complicated. Based on your description, I assume that the card is
not connected to a monitor or that this monitor will not be used for
viewing. If that's not the case, the answers below are going to be

First, you need to define "accelerated":
* if you mean OpenGL acceleration - which is often enough, then this
will do what you want and is supported:
* if you want to use the regular "nvidia" X11 driver for acceleration
directly, there are ways to use a regular X11 server (usually running as
root) to replace xpra's Xvfb, you may need to use the "
ConnectedMonitor" option if no monitor is attached to the card. This
will only work for a single user per card and your mileage may vary: it
"should" work.
Using "xpra shadow" to copy an existing display is not a good solution
at present as it uses polling and will use far too much CPU time -
though that could be fixed.

The main downside of the current xpra 0.11 code is that it is not really
tailored for this Nvidia specific use-case: during screen updates the
pixel data will be downloaded from the GPU to the CPU and then uploaded
again to the GPU for compression... which is a complete waste of
valuable memory bandwidth. It shouldn't be too hard to bypass this
unnecessary copying, and if there is enough demand for it then we can
certainly look at it.
> If not, is this something that some other VNC like program can do?
Not as far as I know: xpra is the first, and at present the only
open-source software to have NVENC support.
>   If so,
> are there any other hardware requirements or issues that I should know
> about?  Would any kepler/NVENC enabled nvidia card be able to do this?
As per above, with consumer cards (GeForce) you will need to find a
license key...

I do wonder if some consumer protection law could force Nvidia to
provide the keys required to take advantage of the features they
advertised when the cards were sold (and earlier SDKs did not require
license keys either).
As can be seen here in the GTX680 whitepaper:
"All Kepler GPUs also incorporate a new hardware-based H.264 video
encoder, NVENC.  "
> Does anyone have any experience with this?


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