fix(engine): audio encodes on FFmpeg 4.4, which has no setts duration option

packages/engine/src/services/aacEncode.test.ts

@@ -3,7 +3,7 @@ import { mkdtempSync, readFileSync, rmSync, writeFileSync } from "node:fs";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { afterAll, describe, expect, it, vi } from "vitest";
-import { getFfmpegBinary, getFfprobeBinary } from "../utils/ffmpegBinaries.js";
+import { FFMPEG_PATH_ENV, getFfmpegBinary, getFfprobeBinary } from "../utils/ffmpegBinaries.js";
 import { aacSegmentCount, encodeAac, splitAdtsFrames } from "./aacEncode.js";
 import * as ffmpegRunner from "../utils/runFfmpeg.js";
 
@@ -196,6 +196,39 @@ describe.skipIf(!HAS_FFMPEG)("encodeAac", () => {
     expect(streamEnd(split)).toBe(streamEnd(single));
   }, 120_000);
 
+  it.skipIf(process.platform === "win32")(
+    "ends the stream at the duration on an FFmpeg whose setts has no duration option",
+    async () => {
+      const source = join(dir, "old-ffmpeg.wav");
+      ffmpeg(["-f", "lavfi", "-i", "sine=f=440:d=2.5:r=48000", "-ac", "2", "-y", source]);
+      const wrapper = join(dir, "ffmpeg-without-setts-duration");
+      writeFileSync(
+        wrapper,
+        [
+          "#!/bin/sh",
+          'case "$*" in *"-h bsf=setts"*) exit 0;; esac',
+          `case "$*" in *"setts=duration"*) echo "Option 'duration' not found" >&2; exit 1;; esac`,
+          `exec "${getFfmpegBinary()}" "$@"`,
+        ].join("\n"),
+        { mode: 0o755 },
+      );
+      const reference = join(dir, "old-ffmpeg-reference.m4a");
+      expect((await encodeAac(source, reference, 2.5, { timeout: 30_000 })).success).toBe(true);
+
+      const saved = process.env[FFMPEG_PATH_ENV];
+      process.env[FFMPEG_PATH_ENV] = wrapper;
+      const coded = join(dir, "old-ffmpeg.m4a");
+      try {
+        expect((await encodeAac(source, coded, 2.5, { timeout: 30_000 })).success).toBe(true);
+      } finally {
+        if (saved === undefined) delete process.env[FFMPEG_PATH_ENV];
+        else process.env[FFMPEG_PATH_ENV] = saved;
+      }
+      expect(streamEnd(coded)).toBe(streamEnd(reference));
+    },
+    60_000,
+  );
+
   it("keeps a sharp onset at its level when the audio opens quietly, encode after encode", async () => {
     const growthDb: number[] = [];
     for (const f0 of [250, 306, 360]) {

packages/engine/src/services/aacEncode.ts

@@ -3,8 +3,10 @@
  * so long audio is encoded as frame-aligned segments in parallel and their frames joined.
  */
 
+import { execFile } from "node:child_process";
 import { mkdtempSync, readFileSync, rmSync, writeFileSync } from "node:fs";
 import { dirname, join } from "node:path";
+import { getFfmpegBinary } from "../utils/ffmpegBinaries.js";
 import { runFfmpeg, type RunFfmpegResult } from "../utils/runFfmpeg.js";
 
 const SAMPLE_RATE = 48_000;
@@ -55,6 +57,35 @@ function planSegments(totalDuration: number, count: number) {
   });
 }
 
+const settsDurationSupport = new Map<string, Promise<boolean>>();
+
+/** FFmpeg before 5.0 (Ubuntu 22.04 ships 4.4) has no `duration` option on the setts filter. */
+function supportsSettsDuration(binary = getFfmpegBinary()): Promise<boolean> {
+  let supported = settsDurationSupport.get(binary);
+  if (!supported) {
+    supported = new Promise((resolve) => {
+      execFile(binary, ["-hide_banner", "-h", "bsf=setts"], (error, stdout) => {
+        // A binary that cannot even print help fails the encode with its own error, not this one.
+        resolve(error !== null || stdout.includes("duration"));
+      });
+    });
+    settsDurationSupport.set(binary, supported);
+  }
+  return supported;
+}
+
+function encodeInOnePass(
+  input: string,
+  outputPath: string,
+  { signal, timeout, filter }: { signal?: AbortSignal; timeout: number; filter?: string },
+): Promise<RunFfmpegResult> {
+  const filters = [filter, `aresample=${SAMPLE_RATE}`].filter(Boolean).join(",");
+  return runFfmpeg(["-i", input, "-af", filters, ...AAC_ARGS, "-y", outputPath], {
+    signal,
+    timeout,
+  });
+}
+
 /** `input`, after `filter`, is audio of exactly `totalDuration`. */
 export async function encodeAac(
   input: string,
@@ -67,6 +98,9 @@ export async function encodeAac(
     segments: count = aacSegmentCount(totalDuration),
   }: { signal?: AbortSignal; timeout: number; filter?: string; segments?: number },
 ): Promise<RunFfmpegResult> {
+  if (!(await supportsSettsDuration())) {
+    return encodeInOnePass(input, outputPath, { signal, timeout, filter });
+  }
   const dir = mkdtempSync(join(dirname(outputPath), ".aac-segments-"));
   try {
     const segments = planSegments(totalDuration, count).map((segment, k) => ({