feat(ffmpeg): add wav-3cx telephony preset and URL-param format pre-selection

[gingeekrishna]

Closes #559.

Changes

1. WAV preset for 3CX telephony (wav-3cx)

Adds a wav-3cx output target to the FFmpeg converter that produces a WAV file with the exact parameters required by 3CX and similar telephony systems — no post-processing needed:

Parameter	Value
Channels	Mono (-ac 1)
Sample rate	8 kHz (-ar 8000)
Bit depth	16-bit PCM (-sample_fmt s16)

The option appears in the UI under the ffmpeg group alongside the regular wav target. normalizeOutputFiletype maps wav-3cx → wav so the downloaded file has the standard .wav extension that telephony systems expect.

Before: upload → convert to wav → open in 3CX converter → set mono/8kHz/16-bit → done
After: upload → convert to wav-3cx → done

2. URL query-param format pre-selection

Adds support for ?to=<format>&converter=<name> query parameters on the root page. When a user arrives with these set, the format selector is automatically pre-populated as soon as conversion options finish loading (after the first file is selected).

http://localhost:3000/?to=wav-3cx&converter=ffmpeg

This lets teams share a direct link for their most-used conversion, bookmarked or embedded in a workflow.

The converter param is optional — omitting it picks the first converter that offers the target format:

http://localhost:3000/?to=wav-3cx

Implementation notes

• Follows the existing compound-format-ID pattern (av1.mkv, h264.mp4, glb2 → glb, etc.) — no new abstractions needed.
• The auto-selection runs entirely in script.js after the dynamic /conversions fetch resolves; no backend changes required.
• If ?to refers to a format not available for the uploaded file type, the param is silently ignored (the target button simply won't exist in the DOM).

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Summary by cubic

Adds a wav-3cx preset and URL-parameter preselection for one-click 3CX/telephony conversions, reducing clicks and enforcing correct WAV settings by default. Previously users converted to wav and set mono/8 kHz/16‑bit manually; now wav-3cx enforces these, and links can prefill the target format.

• wav-3cx output: mono, 8 kHz, 16‑bit PCM (forces -c:a pcm_s16le). Appears under ffmpeg. normalizeOutputFiletype maps wav-3cx to wav so downloads use .wav.
• URL preselection: ?to=<format>&converter=<name> auto-fills the target after options load; unavailable pairs are ignored. Uses dataset matching to avoid selector-related errors from special characters in params.

^{Written for commit 56cb6e4. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 3 files

_{Re-trigger cubic}

[Copilot]

Pull request overview

This PR adds a dedicated FFmpeg output preset for 3CX-compatible WAV exports and introduces URL query parameters that pre-select the target format (and optionally the converter) on the main page to streamline repeated conversions.

Changes:

• Add wav-3cx as an FFmpeg output target and normalize its download extension to .wav.
• Apply a 3CX telephony audio preset (mono, 8 kHz, 16-bit) during FFmpeg conversion when wav-3cx is selected.
• Support ?to=<format>&converter=<name> URL params to auto-select the desired target format after conversion options load.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/helpers/normalizeFiletype.ts	Maps wav-3cx to .wav so downloads use a standard WAV extension.
src/converters/ffmpeg.ts	Registers wav-3cx and applies extra FFmpeg audio arguments for the telephony preset.
public/script.js	Parses to / converter query params and auto-selects the matching conversion target in the UI.

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