ximagesrc at 144 fps

[Nicolas Dufresne]

Le sam. 25 avr. 2020 22 h 00, Daniel Johnson <teknotus at gmail.com> a écrit :

> If you are interested in better performance and better rate, you will
>> have to move on with gnome-shell Wayland and use the Screencast portal
>> to request a pipewire stream. This requires some programming though, of
>> course a project to make a gst source could be nice.
>>
>>
>> Unless they have massively fixed it since the last time I tried it I
>> wouldn't recommend the gnome-shell recorder. It tended to instantly freeze
>> my desktop so that I couldn't recover without hitting the power button. I
>> was horrified when I looked at the source code. Basically if I remember
>> correctly dropped in a chunk of gst-launch passed in from another program
>> as a string via dbus and ran it directly in the same thread that listened
>> for keypresses and drew the screen. So any gstreamer pipeline issues that
>> keep the thread busy will mean no recovery.
>
>
I'm referring to Screencast portal. This comment seems to mix multiple
topics together in order to support a rant.

No one have touched ximagesrc for a long time, feel free to give it some
love, it's old and slightly deprecated, but it haven't worked well since
the introduction of GL compositors (at least that's what my memory thinks
is the trip point). Note that normally how damage should work would be to
download the damage from xserver and apply the delta on top of a copy of
the full previous frames. That's what we do in rfbsrc (known as VNC).
GStreamer does not have mechanisms to stream damages. This also mean it
would be a very bad base for VNC server, or other damage.

With the Screencast portal (also works on KDE btw), the compositor can
zero-copy the full rendered image through pipewire, which is a better fit
for streaming. There is still some work to enable zero-copy with another GL
pipeline, or VAAPI encoder, but this is being worked on. The portal
implement X11 fallback for folks on X11.

I use this regularly inside video conference and for wifi display, I doubt
my experience is unique. It also ensure that as a user I'm aware that
someone is spying on my screen. With X11, any background process can do
that silently.


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