improved web ui, upload is sorta better, 5sec advertise btn

app/wav.js

@@ -27,13 +27,13 @@ async function decodeMono(arrayBuffer, rate) {
   return { samples: rendered.getChannelData(0), rate, srcRate: decoded.sampleRate };
 }
 
-function floatToPcm(samples, bits) {
+function floatToPcm(samples, bits, gain = 1) {
   const n = samples.length;
   if (bits === 16) {
     const out = new Uint8Array(n * 2);
     const dv = new DataView(out.buffer);
     for (let i = 0; i < n; i++) {
-      let s = Math.max(-1, Math.min(1, samples[i]));
+      let s = Math.max(-1, Math.min(1, samples[i] * gain));
       dv.setInt16(i * 2, Math.round(s * 32767), true); // signed LE
     }
     return out;
@@ -41,7 +41,7 @@ function floatToPcm(samples, bits) {
   // 8-bit unsigned PCM, center 128
   const out = new Uint8Array(n);
   for (let i = 0; i < n; i++) {
-    let s = Math.max(-1, Math.min(1, samples[i]));
+    let s = Math.max(-1, Math.min(1, samples[i] * gain));
     out[i] = Math.max(0, Math.min(255, Math.round(s * 127) + 128));
   }
   return out;
@@ -88,10 +88,11 @@ export function trimSamples(samples, rate, trimStart = 0, trimEnd = 0) {
   return samples.subarray(start, end);
 }
 
-// Encode mono Float32 samples to a WAV. Returns { wav, durationSec }.
-export function encodeWav(samples, rate, bits, { trimStart = 0, trimEnd = 0 } = {}) {
+// Encode mono Float32 samples to a WAV, applying an optional per-track `gain`
+// (1 = unchanged) that is baked into the samples. Returns { wav, durationSec }.
+export function encodeWav(samples, rate, bits, { trimStart = 0, trimEnd = 0, gain = 1 } = {}) {
   const sliced = trimSamples(samples, rate, trimStart, trimEnd);
-  const pcm = floatToPcm(sliced, bits);
+  const pcm = floatToPcm(sliced, bits, gain);
   const wav = buildWav(pcm, rate, bits);
   return { wav, durationSec: sliced.length / rate };
 }