Surface ffmpeg startup failures

src/audio-manager.ts

@@ -108,6 +108,12 @@ export default class AudioManager {
         const resolvedSource = this.resolveSource();
         this.stopCurrentPlayback();
         this.ffmpeg = startFfmpeg(resolvedSource.input, this.options.ffmpeg);
+        try {
+            await this.ffmpeg.ready;
+        } catch (error) {
+            this.stopCurrentPlayback();
+            throw error;
+        }
         this.resource = createAudioResource(this.ffmpeg.process.stdout, {
             inputType: StreamType.Raw,
             inlineVolume: this.options.volume?.enabled === true,

src/ffmpeg.ts

@@ -3,7 +3,7 @@ import type { ChildProcessByStdio } from 'node:child_process';
 import { createRequire } from 'node:module';
 import type { Readable } from 'node:stream';
 
-import { AudioManagerConfigError } from './errors';
+import { AudioManagerConfigError, FfmpegProcessError } from './errors';
 import type { FfmpegOptions } from './types';
 
 const requireFromCurrentModule = createRequire(__filename);
@@ -11,9 +11,11 @@ const requireFromCurrentModule = createRequire(__filename);
 const DEFAULT_INPUT_ARGS = ['-hide_banner', '-loglevel', 'error', '-nostdin'] as const;
 const DEFAULT_OUTPUT_ARGS = ['-vn', '-f', 's16le', '-ar', '48000', '-ac', '2', 'pipe:1'] as const;
 const FORCE_KILL_TIMEOUT_MS = 2_000;
+const STDERR_TAIL_BYTES = 4_096;
 
 export type FfmpegProcessHandle = {
     process: ChildProcessByStdio<null, Readable, Readable>;
+    ready: Promise<void>;
     stop(): void;
 };
 
@@ -50,18 +52,65 @@ export function startFfmpeg(input: string, options: FfmpegOptions = {}): FfmpegP
         ...(options.outputArgs ?? DEFAULT_OUTPUT_ARGS),
     ];
     const childProcess = spawn(executable, args, { stdio: ['ignore', 'pipe', 'pipe'] });
+    const ready = waitForFfmpegOutput(childProcess);
 
-    childProcess.once('error', () => undefined);
     childProcess.stderr.resume();
 
     return {
         process: childProcess,
+        ready,
         stop: (): void => {
             stopProcess(childProcess);
         },
     };
 }
 
+function waitForFfmpegOutput(childProcess: ChildProcessByStdio<null, Readable, Readable>): Promise<void> {
+    let stderrTail = '';
+
+    const appendStderr = (chunk: Buffer | string): void => {
+        stderrTail = (stderrTail + String(chunk)).slice(-STDERR_TAIL_BYTES);
+    };
+
+    childProcess.stderr.on('data', appendStderr);
+
+    return new Promise((resolve, reject) => {
+        const cleanup = (): void => {
+            childProcess.off('error', onError);
+            childProcess.off('exit', onExit);
+            childProcess.stdout.off('readable', onReadable);
+        };
+
+        const fail = (message: string, cause?: unknown): void => {
+            cleanup();
+            reject(new FfmpegProcessError(addStderrTail(message, stderrTail), cause));
+        };
+
+        const onError = (error: Error): void => {
+            fail(`Unable to start ffmpeg. Cause: ${error.message}`, error);
+        };
+
+        const onExit = (code: number | null, signal: NodeJS.Signals | null): void => {
+            fail(`ffmpeg exited before producing audio. Exit code: ${code ?? 'none'}, signal: ${signal ?? 'none'}.`);
+        };
+
+        const onReadable = (): void => {
+            cleanup();
+            resolve();
+        };
+
+        childProcess.once('error', onError);
+        childProcess.once('exit', onExit);
+        childProcess.stdout.once('readable', onReadable);
+    });
+}
+
+function addStderrTail(message: string, stderrTail: string): string {
+    const trimmedTail = stderrTail.trim();
+
+    return trimmedTail ? `${message} stderr: ${trimmedTail}` : message;
+}
+
 function stopProcess(childProcess: ChildProcessByStdio<null, Readable, Readable>): void {
     childProcess.stdout.destroy();
     childProcess.stderr.destroy();

tests/audio-manager.test.ts

@@ -4,7 +4,7 @@ import { resolve } from 'node:path';
 import { PassThrough } from 'node:stream';
 
 import AudioManager from '../src/audio-manager';
-import { AudioManagerConfigError, AudioManagerStateError } from '../src';
+import { AudioManagerConfigError, AudioManagerStateError, FfmpegProcessError } from '../src';
 import { startFfmpeg } from '../src/ffmpeg';
 import type { AudioSource, VoiceConnectionOptions } from '../src';
 
@@ -31,6 +31,7 @@ const mockFfmpegHandle = {
     process: {
         stdout: new PassThrough(),
     },
+    ready: Promise.resolve(),
     stop: jest.fn(),
 };
 
@@ -163,6 +164,26 @@ describe('AudioManager', () => {
         expect(manager.state).toBe('playing');
     });
 
+    it('does not report playback when ffmpeg startup fails', async () => {
+        const startupError = new FfmpegProcessError('Unable to start ffmpeg.');
+        jest.mocked(startFfmpeg).mockReturnValueOnce({
+            ...mockFfmpegHandle,
+            ready: Promise.reject(startupError),
+        });
+        const manager = new AudioManager({
+            connection: connectionOptions,
+            source: liveStreamSource,
+            renewIntervalMs: false,
+        });
+
+        await manager.connect();
+        await expect(manager.play()).rejects.toBe(startupError);
+
+        expect(manager.state).toBe('ready');
+        expect(mockAudioPlayer.play).not.toHaveBeenCalled();
+        expect(mockFfmpegHandle.stop).toHaveBeenCalledTimes(1);
+    });
+
     it('replaces active playback when a new source is played', async () => {
         const manager = new AudioManager({
             connection: connectionOptions,

tests/ffmpeg.test.ts

@@ -1,6 +1,7 @@
 import { jest, describe, beforeEach, afterEach, it, expect } from '@jest/globals';
 import { spawn } from 'node:child_process';
 
+import { FfmpegProcessError } from '../src';
 import { resolveFfmpegExecutable, startFfmpeg } from '../src/ffmpeg';
 
 jest.mock('node:child_process', () => ({
@@ -12,12 +13,16 @@ const mockSpawn = jest.mocked(spawn);
 type MockChildProcess = {
     stdout: {
         destroy: jest.Mock;
+        once: jest.Mock;
+        off: jest.Mock;
     };
     stderr: {
         destroy: jest.Mock;
+        on: jest.Mock;
         resume: jest.Mock;
     };
     once: jest.Mock;
+    off: jest.Mock;
     removeAllListeners: jest.Mock;
     kill: jest.Mock;
     killed: boolean;
@@ -29,12 +34,16 @@ function createMockChildProcess(): MockChildProcess {
     return {
         stdout: {
             destroy: jest.fn(),
+            once: jest.fn(),
+            off: jest.fn(),
         },
         stderr: {
             destroy: jest.fn(),
+            on: jest.fn(),
             resume: jest.fn(),
         },
         once: jest.fn(),
+        off: jest.fn(),
         removeAllListeners: jest.fn(),
         kill: jest.fn(),
         killed: false,
@@ -88,9 +97,39 @@ describe('ffmpeg helpers', () => {
             { stdio: ['ignore', 'pipe', 'pipe'] },
         );
         expect(childProcess.once).toHaveBeenCalledWith('error', expect.any(Function));
+        expect(childProcess.once).toHaveBeenCalledWith('exit', expect.any(Function));
+        expect(childProcess.stdout.once).toHaveBeenCalledWith('readable', expect.any(Function));
+        expect(childProcess.stderr.on).toHaveBeenCalledWith('data', expect.any(Function));
         expect(childProcess.stderr.resume).toHaveBeenCalledTimes(1);
     });
 
+    it('rejects readiness when ffmpeg startup emits an error', async () => {
+        const childProcess = createMockChildProcess();
+        mockSpawn.mockReturnValue(childProcess);
+
+        const handle = startFfmpeg('tests/audio.mp3');
+        const errorHandler = childProcess.once.mock.calls.find(([event]) => event === 'error')?.[1];
+
+        errorHandler(new Error('spawn ENOENT'));
+
+        await expect(handle.ready).rejects.toThrow(FfmpegProcessError);
+        await expect(handle.ready).rejects.toThrow('spawn ENOENT');
+    });
+
+    it('includes stderr when ffmpeg exits before producing audio', async () => {
+        const childProcess = createMockChildProcess();
+        mockSpawn.mockReturnValue(childProcess);
+
+        const handle = startFfmpeg('tests/audio.mp3');
+        const stderrHandler = childProcess.stderr.on.mock.calls.find(([event]) => event === 'data')?.[1];
+        const exitHandler = childProcess.once.mock.calls.find(([event]) => event === 'exit')?.[1];
+
+        stderrHandler('invalid input');
+        exitHandler(1, null);
+
+        await expect(handle.ready).rejects.toThrow('invalid input');
+    });
+
     it('uses custom executable and argument overrides when provided', () => {
         const childProcess = createMockChildProcess();
         mockSpawn.mockReturnValue(childProcess);