Video recording presets for Spectacle

Development Info

Merge Request: https://invent.kde.org/friedreich/kpipewire/-/compare/master...work%2Fencoding-preferences?from_project_id=1911 Work in Progress
Merge Request: https://invent.kde.org/friedreich/spectacle/-/compare/master...work%2Fencoding-preferences?from_project_id=2004 Work in Progress

I want the ability to configure the encoding preferences for video recordings in Spectacle. This is useful for users who want to optimize for file size, quality, or speed. I also want to be able to benchmark the different encoding preferences to actually see the difference in file size and quality.

Spectacle Settings UI

Users can now explicitly set a Max frame rate (defaulting to 30 fps) and choose an Encoding preference (Balanced, Highest Quality, Fast, or Smallest Size).

KPipeWire Backend

I refactored the backend to ensure that these preferences are actually respected by all encoders

Benchmarks

To allow benchmarking I added cli options to Spectacle for running headless recordings with varying encoders, frame rates and presets.

The results of my testing across 48 combinations show the impact of these presets (10-second recordings):

Format	Preset	10 FPS	60 FPS	120 FPS
vp9	balanced	125.9 KiB	460.4 KiB	473.3 KiB
vp9	quality	169.8 KiB	491.9 KiB	495.7 KiB
vp9	speed	195.2 KiB	568.5 KiB	573.3 KiB
vp9	size	159.8 KiB	312.8 KiB	444.9 KiB
h264	balanced	110.7 KiB	408.1 KiB	415.6 KiB
h264	quality	118.7 KiB	433.1 KiB	438.5 KiB
h264	speed	119.8 KiB	446.2 KiB	437.7 KiB
h264	size	210.7 KiB	460.9 KiB	468.6 KiB
webp	balanced	8.69 MiB	29.37 MiB	29.86 MiB
webp	quality	8.35 MiB	30.19 MiB	31.32 MiB
webp	speed	15.94 MiB	42.60 MiB	41.22 MiB
webp	size	8.40 MiB	31.67 MiB	32.90 MiB
gif	balanced	425.6 KiB	635.7 KiB	616.3 KiB
gif	quality	14.44 MiB	48.22 MiB	51.51 MiB
gif	speed	356.1 KiB	499.5 KiB	433.4 KiB
gif	size	392.8 KiB	537.2 KiB	496.3 KiB