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

WAV preset for 3CX / telephony systems
---------------------------------------
Adds `wav-3cx` as a new FFmpeg output target that produces a WAV file
with the parameters required by 3CX and similar telephony platforms:
  - Channel: mono   (-ac 1)
  - Sample rate: 8 kHz  (-ar 8000)
  - Bit depth: 16-bit PCM  (-sample_fmt s16)

The target appears in the UI alongside the regular `wav` option under the
ffmpeg converter group.  `normalizeOutputFiletype` maps `wav-3cx` → `wav`
so the downloaded file has the correct `.wav` extension.

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

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

Closes #559

Signed-off-by: Radhakrishnan Pachyappan <gingeekrishna@gmail.com>

public/script.js

@@ -7,6 +7,10 @@ let fileType;
 let pendingFiles = 0;
 let formatSelected = false;
 
+const urlParams = new URLSearchParams(window.location.search);
+const defaultTo = urlParams.get("to");
+const defaultConverter = urlParams.get("converter");
+
 dropZone.addEventListener("dragover", (e) => {
   e.preventDefault();
   dropZone.classList.add("dragover");
@@ -59,6 +63,23 @@ function handleFile(file) {
       .then((html) => {
         selectContainer.innerHTML = html;
         updateSearchBar();
+
+        if (defaultTo) {
+          const selector = defaultConverter
+            ? `.target[data-value="${defaultTo},${defaultConverter}"]`
+            : `.target[data-target="${defaultTo}"]`;
+          const targetBtn = document.querySelector(selector);
+          if (targetBtn) {
+            const convertToEl = document.querySelector("select[name='convert_to']");
+            const convertToInputEl = document.querySelector("input[name='convert_to_search']");
+            convertToEl.value = targetBtn.dataset.value;
+            convertToInputEl.value = `${targetBtn.dataset.target} using ${targetBtn.dataset.converter}`;
+            formatSelected = true;
+            if (pendingFiles === 0 && fileNames.length > 0) {
+              convertButton.disabled = false;
+            }
+          }
+        }
       })
       .catch(console.error);
   }

src/converters/ffmpeg.ts

@@ -670,6 +670,7 @@ export const properties = {
       "vvc",
       "w64",
       "wav",
+      "wav-3cx",
       "wbmp",
       "webm",
       "webp",
@@ -708,6 +709,11 @@ export async function convert(
     message = "Done: resized to 256x256";
   }
 
+  if (convertTo === "wav-3cx") {
+    // 3CX telephony preset: mono, 8 kHz, 16-bit PCM
+    extraArgs.push("-ac", "1", "-ar", "8000", "-sample_fmt", "s16");
+  }
+
   if (convertTo.split(".").length > 1) {
     // Support av1.mkv and av1.mp4 and h265.mp4 etc.
     const split = convertTo.split(".");

src/helpers/normalizeFiletype.ts

@@ -49,6 +49,8 @@ export const normalizeOutputFiletype = (filetype: string): string => {
       return "fbx";
     case "assjson":
       return "json";
+    case "wav-3cx":
+      return "wav";
     default:
       return lowercaseFiletype;
   }