refactor(media): add shared ffmpeg helpers

src/media/ffmpeg-exec.test.ts

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+import { describe, expect, it } from "vitest";
+import { parseFfprobeCodecAndSampleRate, parseFfprobeCsvFields } from "./ffmpeg-exec.js";
+
+describe("parseFfprobeCsvFields", () => {
+  it("splits ffprobe csv output across commas and newlines", () => {
+    expect(parseFfprobeCsvFields("opus,\n48000\n", 2)).toEqual(["opus", "48000"]);
+  });
+});
+
+describe("parseFfprobeCodecAndSampleRate", () => {
+  it("parses opus codec and numeric sample rate", () => {
+    expect(parseFfprobeCodecAndSampleRate("Opus,48000\n")).toEqual({
+      codec: "opus",
+      sampleRateHz: 48_000,
+    });
+  });
+
+  it("returns null sample rate for invalid numeric fields", () => {
+    expect(parseFfprobeCodecAndSampleRate("opus,not-a-number")).toEqual({
+      codec: "opus",
+      sampleRateHz: null,
+    });
+  });
+});

src/media/ffmpeg-exec.ts

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+import { execFile, type ExecFileOptions } from "node:child_process";
+import { promisify } from "node:util";
+import {
+  MEDIA_FFMPEG_MAX_BUFFER_BYTES,
+  MEDIA_FFMPEG_TIMEOUT_MS,
+  MEDIA_FFPROBE_TIMEOUT_MS,
+} from "./ffmpeg-limits.js";
+
+const execFileAsync = promisify(execFile);
+
+export type MediaExecOptions = {
+  timeoutMs?: number;
+  maxBufferBytes?: number;
+};
+
+function resolveExecOptions(
+  defaultTimeoutMs: number,
+  options: MediaExecOptions | undefined,
+): ExecFileOptions {
+  return {
+    timeout: options?.timeoutMs ?? defaultTimeoutMs,
+    maxBuffer: options?.maxBufferBytes ?? MEDIA_FFMPEG_MAX_BUFFER_BYTES,
+  };
+}
+
+export async function runFfprobe(args: string[], options?: MediaExecOptions): Promise<string> {
+  const { stdout } = await execFileAsync(
+    "ffprobe",
+    args,
+    resolveExecOptions(MEDIA_FFPROBE_TIMEOUT_MS, options),
+  );
+  return stdout.toString();
+}
+
+export async function runFfmpeg(args: string[], options?: MediaExecOptions): Promise<string> {
+  const { stdout } = await execFileAsync(
+    "ffmpeg",
+    args,
+    resolveExecOptions(MEDIA_FFMPEG_TIMEOUT_MS, options),
+  );
+  return stdout.toString();
+}
+
+export function parseFfprobeCsvFields(stdout: string, maxFields: number): string[] {
+  return stdout
+    .trim()
+    .toLowerCase()
+    .split(/[,\r\n]+/, maxFields)
+    .map((field) => field.trim());
+}
+
+export function parseFfprobeCodecAndSampleRate(stdout: string): {
+  codec: string | null;
+  sampleRateHz: number | null;
+} {
+  const [codecRaw, sampleRateRaw] = parseFfprobeCsvFields(stdout, 2);
+  const codec = codecRaw ? codecRaw : null;
+  const sampleRate = sampleRateRaw ? Number.parseInt(sampleRateRaw, 10) : Number.NaN;
+  return {
+    codec,
+    sampleRateHz: Number.isFinite(sampleRate) ? sampleRate : null,
+  };
+}

src/media/ffmpeg-limits.ts

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+export const MEDIA_FFMPEG_MAX_BUFFER_BYTES = 10 * 1024 * 1024;
+export const MEDIA_FFPROBE_TIMEOUT_MS = 10_000;
+export const MEDIA_FFMPEG_TIMEOUT_MS = 45_000;
+export const MEDIA_FFMPEG_MAX_AUDIO_DURATION_SECS = 20 * 60;

src/media/temp-files.ts

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+import fs from "node:fs/promises";
+
+export async function unlinkIfExists(filePath: string | null | undefined): Promise<void> {
+  if (!filePath) {
+    return;
+  }
+  try {
+    await fs.unlink(filePath);
+  } catch {
+    // Best-effort cleanup for temp files.
+  }
+}