fix(pipewire): revert back to compositor-side pacing

[psyke83]

Description

KWin 5.x/6.x has poor frame pacing when not using variable rate capture for screencasting, but KWin 6.7 also breaks desktop animation pacing - which runs at half speed - when variable rate capture (0/1) is negotiated.

The upcoming KWin 6.8 improves pacing for non-variable rate capture, so if we switch back to capture using a negotiated target maxFramerate, we can also fix desktop animation pacing.

This change also avoids first-time negotiation failure for mutter, but we can retain the negotiate_maxframerate_ fallback to negotiate the target fps only via SPA_FORMAT_VIDEO_framerate, just in case there are other compositors that don't handle maxFramerate negotiation robustly.

Screenshot

Issues Fixed or Closed

Roadmap Issues

Type of Change

• feat: New feature (non-breaking change which adds functionality)
• fix: Bug fix (non-breaking change which fixes an issue)
• docs: Documentation only changes
• style: Changes that do not affect the meaning of the code (white-space, formatting, missing semicolons, etc.)
• refactor: Code change that neither fixes a bug nor adds a feature
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• test: Adding missing tests or correcting existing tests
• build: Changes that affect the build system or external dependencies
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• chore: Other changes that don't modify src or test files
• revert: Reverts a previous commit
• BREAKING CHANGE: Introduces a breaking change (can be combined with any type above)

Checklist

• Code follows the style guidelines of this project
• Code has been self-reviewed
• Code has been commented, particularly in hard-to-understand areas
• Code docstring/documentation-blocks for new or existing methods/components have been added or updated
• Unit tests have been added or updated for any new or modified functionality

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[psyke83]

Technically I'm happy with the change as-is, but I'm keeping it in draft as it's a quasi-breaking change until Plasma 6.8 releases in October, or if the related fix for improved pacing gets backported to older branches.

Summary of effects:

• Mutter/GNOME: no downsides. Sunshine will no longer need to renegotiate pipewire session on first probe, so it's an overall improvement.
• Users of KWin 5.x-6.7 will see overall pacing get worse (1% skew or ~57fps on a 60fps stream).
• Users of KWin 6.7 will see the general 1% pacing skew, but desktop animations will run at proper speed (albeit with the same 1% skew).
• Users of KWin 6.8 will have good pacing for both desktop animations and general/in-game pacing.

If anyone is interested in testing the improved pacing, it's trivial to manually backport the single commit to KWin 6.7.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud