[Plugin] Add fil4.lv2

[kmturley]

Adds fil4.lv2 (x42-eq), a 4-band parametric EQ with low/high shelf filters and an optional custom GUI showing the transfer function and realtime spectrum (mac/win/linux, GPL-2.0).

From the RX 12 replacements list in #527 (EQ alternative). Unlike other x42.lv2 repos checked recently (fat1.lv2, meters.lv2, darc.lv2, dpl.lv2), this one does have real GitHub release binaries.

[github-actions]

VirusTotal Report:

• test/downloads/x42/fil4.lv2/0.4.4/4-x42-eq-v0.4.4-w64-Setup.exe
• test/downloads/x42/fil4.lv2/0.4.4/3-x42-eq-v0.4.4-w32-Setup.exe
• test/downloads/x42/fil4.lv2/0.4.4/2-x42-eq-v0.4.4-OSX.dmg
• test/downloads/x42/fil4.lv2/0.4.4/1-x42-eq-v0.4.4-linux-x86_64.tar.gz
• test/downloads/x42/fil4.lv2/0.4.4/0-x42-eq-v0.4.4-linux-i386.tar.gz

[github-actions]

Destination urls:
Registry: https://open-audio-stack.github.io/open-audio-stack-registry/plugins/x42/fil4.lv2
Site: https://studiorack.github.io/studiorack-site/plugins/x42/fil4.lv2

[github-actions]

Plugin author notification:

@x42 — your plugin has been submitted to the Open Audio Stack registry. Please review this PR and let us know if the metadata (name, description, tags, files) is correct. To see a full list of all currently added plugins, click here.

[x42]

Thanks for the heads up. Those binaries are more than a decade old and outdated.
Current release is 0.8.11

[kmturley]

@x42 Thanks but I don't see binaries on that Release?
https://github.com/x42/fil4.lv2/releases/v0.8.11

[x42]

As I mentioned at x42/fat1.lv2#31 (comment) there are no plans to provide official binary releases on 3rd party sites.

Could you elaborate why Open Audio Stack registry is so focused on github binary releases?

[kmturley]

@x42

The Open Audio Stack (OAS) Registry relies heavily on GitHub Releases and pinned binary URLs as a deliberate architecture choice. Rather than hosting heavy binary files on a centralized server, OAS operates as a lightweight, static metadata index.

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Key Reasons for Relying on GitHub Binary Releases

1. Zero Infrastructure Costs for Open-Source Software

Audio plugins, presets, and sample libraries require significant storage space and bandwidth. Because OAS is tailored primarily for free and open-source audio software, hosting gigabytes of binary downloads directly on a central server would be cost-prohibitive. Offloading asset storage to GitHub Releases allows the project to remain entirely free, open, and community-maintained.

2. Immutability and Cryptographic Security ($SHA-256$)

OAS enforces strict security and package integrity through strict validation rules:

• Every package entry requires a verified sha256 hash and exact file size matching.
• GitHub Releases (and commit-pinned repository URLs) provide immutable links—the file contents and cryptographic hash will never change unexpectedly.
• Dynamic branch zips (e.g., downloading a main branch archive) change their hash whenever new code is pushed, which triggers security validation errors in the OAS index.

3. Seamless Developer CI/CD Workflows

Most open-source plugin developers already build, cross-compile (Windows, macOS, Linux), and attach binaries to GitHub Releases using automated CI/CD workflows (such as GitHub Actions).

• Allowing package index entries to point directly to these existing release artifacts eliminates duplicate upload steps for developers.

4. Static Registry Architecture

The OAS registry itself uses automated workflows to validate YAML metadata files submitted via Pull Requests, which then compile into static JSON API files served on GitHub Pages. This makes the entire ecosystem decentralized, resilient, and easy to consume by client tools (such as command-line managers or DAWs) without needing custom database infrastructure.