GStreamer enhancements

[totaam]

Improving upon #3750 and perhaps restoring #3964 in some shape or form.

• zero copy: #3754
• try to use variable refresh rate somehow - GStreamer pipelines mostly used fixed refresh rate, which is a bad fit for us - especially when dealing with bandwidth issues
• focus on vaapi drivers: https://wiki.archlinux.org/title/Hardware_video_acceleration#Comparison_tables
• optimizing our gstreamer pipelines
• honouring bandwidth limit static and dynamic values
• add profiles, so we can mimic other project's settings (ie: vah264enc in selkies - preferably whilst still honouring dynamic speed / quality and bandwidth limit
• can we use GStreamer QoS?

Some links:

• Platform-specific elements
• d3d11screencapturesrc: handle multi-monitor mode better?

[ehfd]

add profiles, so we can mimic other project's settings (ie: vah264enc in selkies - preferably whilst still honouring dynamic speed / quality and bandwidth limit

This hasn't really been tested rigorously and there is a very high chance there is something better. Looking forward to any improvements.

[ehfd]

QOS is typically used in the color converter/scaler as that is typically the earliest point after the source before the encoder.

[totaam]

QOS is typically used in the color converter/scaler as that is typically the earliest point after the source before the encoder.

Ideally for us, we want to incorporate this data into the engine - much earlier than csc / scaling, so we can drop quality / speed / framerate, etc

[totaam]

Good thing we can now disable gstreamer completely as it avoids crashing systems: https://github.com/Xpra-org/xpra/issues/4330#issuecomment-2308760220