fixed most upload issues, updated schematic

app/wav.js

@@ -72,11 +72,26 @@ function buildWav(pcm, rate, bits) {
   return u8;
 }
 
-// Returns { wav: Uint8Array, durationSec, rate, bits, srcRate }.
-export async function fileToWav(file, { rate = 8000, bits = 8 } = {}) {
+// Decode a file to mono Float32 samples at `rate`. This is the expensive step,
+// so callers cache the result and re-encode cheaply when bits/trim change.
+// Returns { samples, rate, srcRate }.
+export async function decodeFileToMono(file, rate = 8000) {
   const arrayBuffer = await file.arrayBuffer();
   const { samples, srcRate } = await decodeMono(arrayBuffer, rate);
-  const pcm = floatToPcm(samples, bits);
-  const wav = buildWav(pcm, rate, bits);
-  return { wav, durationSec: samples.length / rate, rate, bits, srcRate };
+  return { samples, rate, srcRate };
+}
+
+// Slice [trimStart, end-trimEnd] off the mono samples and return that range.
+export function trimSamples(samples, rate, trimStart = 0, trimEnd = 0) {
+  const start = Math.max(0, Math.min(samples.length, Math.floor(trimStart * rate)));
+  const end = Math.max(start, samples.length - Math.max(0, Math.floor(trimEnd * rate)));
+  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 } = {}) {
+  const sliced = trimSamples(samples, rate, trimStart, trimEnd);
+  const pcm = floatToPcm(sliced, bits);
+  const wav = buildWav(pcm, rate, bits);
+  return { wav, durationSec: sliced.length / rate };
 }