src/audio-manager.ts

@@ -82,14 +82,27 @@ export default class AudioManager {
         this.clearRenewTimer();
         this.playbackState = 'connecting';
         this.connection?.destroy();
-        this.connection = joinVoiceChannel({
+        const connection = joinVoiceChannel({
             guildId: this.connectionOptions.guildId,
             channelId: this.connectionOptions.channelId,
             adapterCreator: this.connectionOptions.adapterCreator,
         });
-        this.connection.subscribe(this.audioPlayer);
+        this.connection = connection;
+        connection.subscribe(this.audioPlayer);
 
-        await entersState(this.connection, VoiceConnectionStatus.Ready, this.options.connectTimeoutMs);
+        try {
+            await entersState(connection, VoiceConnectionStatus.Ready, this.options.connectTimeoutMs);
+        } catch (error) {
+            connection.destroy();
+            if (this.connection === connection) {
+                this.connection = undefined;
+            }
+            this.playbackState = 'stopped';
+            throw error;
+        }
+        if (this.connection !== connection) {
+            throw new AudioManagerStateError('Voice connection was stopped before it became ready.');
+        }
         this.playbackState = 'ready';
         this.scheduleRenewal();
     }
@@ -108,17 +121,35 @@ export default class AudioManager {
         const resolvedSource = this.resolveSource();
         this.stopCurrentPlayback();
         this.ffmpeg = startFfmpeg(resolvedSource.input, this.options.ffmpeg);
-        this.resource = createAudioResource(this.ffmpeg.process.stdout, {
-            inputType: StreamType.Raw,
-            inlineVolume: this.options.volume?.enabled === true,
-        });
+        const ffmpeg = this.ffmpeg;
+        try {
+            await ffmpeg.ready;
+            if (this.ffmpeg !== ffmpeg) {
+                throw new AudioManagerStateError('Playback was stopped before ffmpeg became ready.');
+            }
+            this.resource = createAudioResource(ffmpeg.process.stdout, {
+                inputType: StreamType.Raw,
+                inlineVolume: this.options.volume?.enabled === true,
+            });
+        } catch (error) {
+            if (this.ffmpeg === ffmpeg) {
+                this.stopCurrentPlayback();
+            }
+            throw error;
+        }
 
         if (this.options.volume?.enabled === true && this.options.volume.initialPercent !== undefined) {
             this.setVolume(this.options.volume.initialPercent);
         }
 
-        this.audioPlayer.play(this.resource);
-        this.playbackState = 'playing';
+        try {
+            this.audioPlayer.play(this.resource);
+            this.playbackState = 'playing';
+        } catch (error) {
+            this.stopCurrentPlayback();
+            this.playbackState = 'ready';
+            throw error;
+        }
     }
 
     public async start(): Promise<void> {
@@ -169,7 +200,7 @@ export default class AudioManager {
             throw new AudioManagerStateError('Volume control requires volume.enabled to be true.');
         }
 
-        if (volumeInPercent < 0 || volumeInPercent > 100) {
+        if (!Number.isFinite(volumeInPercent) || volumeInPercent < 0 || volumeInPercent > 100) {
             throw new AudioManagerConfigError('Volume must be between 0 and 100 percent.');
         }
 
@@ -227,7 +258,15 @@ export default class AudioManager {
         }
 
         this.renewTimer = setTimeout(() => {
-            void this.start();
+            void this.start().catch(() => {
+                this.clearRenewTimer();
+                this.stopCurrentPlayback();
+                this.audioPlayer.stop(true);
+                this.connection?.disconnect();
+                this.connection?.destroy();
+                this.connection = undefined;
+                this.playbackState = 'stopped';
+            });
         }, renewIntervalMs);
 
         if (typeof this.renewTimer.unref === 'function') {

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

@@ -1,11 +1,14 @@
 import { jest, describe, beforeEach, afterEach, it, expect } from '@jest/globals';
+import { createAudioResource, entersState, joinVoiceChannel } from '@discordjs/voice';
 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 { FfmpegProcessHandle } from '../src/ffmpeg';
 import type { AudioSource, VoiceConnectionOptions } from '../src';
+import type { VoiceConnection } from '@discordjs/voice';
 
 const mockAudioPlayer = {
     play: jest.fn(),
@@ -18,6 +21,13 @@ const mockConnection = {
     disconnect: jest.fn(),
     destroy: jest.fn(),
 };
+const mockSecondConnection = {
+    subscribe: jest.fn(),
+    disconnect: jest.fn(),
+    destroy: jest.fn(),
+};
+const mockVoiceConnection = mockConnection as unknown as VoiceConnection;
+const mockSecondVoiceConnection = mockSecondConnection as unknown as VoiceConnection;
 const mockAudioResource = {
     playStream: {
         destroy: jest.fn(),
@@ -26,10 +36,11 @@ const mockAudioResource = {
         setVolume: jest.fn(),
     },
 };
-const mockFfmpegHandle = {
+const mockFfmpegHandle: FfmpegProcessHandle = {
     process: {
         stdout: new PassThrough(),
-    },
+    } as unknown as FfmpegProcessHandle['process'],
+    ready: Promise.resolve(),
     stop: jest.fn(),
 };
 
@@ -45,8 +56,8 @@ jest.mock('@discordjs/voice', () => ({
     },
     createAudioPlayer: jest.fn(() => mockAudioPlayer),
     createAudioResource: jest.fn(() => mockAudioResource),
-    entersState: jest.fn(() => Promise.resolve(mockConnection)),
-    joinVoiceChannel: jest.fn(() => mockConnection),
+    entersState: jest.fn(() => Promise.resolve(mockVoiceConnection)),
+    joinVoiceChannel: jest.fn(() => mockVoiceConnection),
 }));
 
 jest.mock('../src/ffmpeg', () => ({
@@ -66,6 +77,26 @@ const liveStreamSource: AudioSource = {
 
 const fileSourcePath = 'tests/audio.mp3';
 const resolvedFileSourcePath = resolve(process.cwd(), fileSourcePath);
+type MockedEntersStateReturn = ReturnType<typeof entersState>;
+
+function deferred<T>(): { promise: Promise<T>; resolve: (value: T) => void } {
+    let resolve!: (value: T) => void;
+    const promise = new Promise<T>((promiseResolve) => {
+        resolve = promiseResolve;
+    });
+
+    return { promise, resolve };
+}
+
+function createMockFfmpegHandle(): FfmpegProcessHandle {
+    return {
+        process: {
+            stdout: new PassThrough(),
+        } as unknown as FfmpegProcessHandle['process'],
+        ready: Promise.resolve(),
+        stop: jest.fn(),
+    };
+}
 
 describe('AudioManager', () => {
     beforeEach(() => {
@@ -99,6 +130,91 @@ describe('AudioManager', () => {
         expect(mockAudioPlayer.play).toHaveBeenCalledWith(mockAudioResource);
     });
 
+    it('cleans up when connection startup fails', async () => {
+        jest.useFakeTimers();
+
+        const manager = new AudioManager({
+            connection: connectionOptions,
+            renewIntervalMs: 10_000,
+        });
+        jest.mocked(entersState).mockRejectedValueOnce(new Error('voice connection timeout'));
+
+        await expect(manager.connect()).rejects.toThrow('voice connection timeout');
+
+        expect(manager.state).toBe('stopped');
+        expect(manager.isConnected).toBe(false);
+        expect(mockConnection.subscribe).toHaveBeenCalledWith(mockAudioPlayer);
+        expect(mockConnection.destroy).toHaveBeenCalledTimes(1);
+        expect(jest.getTimerCount()).toBe(0);
+    });
+
+    it('does not become ready when stopped during connection startup', async () => {
+        jest.useFakeTimers();
+        const ready = deferred<VoiceConnection>();
+        jest.mocked(entersState).mockReturnValueOnce(ready.promise as unknown as MockedEntersStateReturn);
+        const manager = new AudioManager({
+            connection: connectionOptions,
+            renewIntervalMs: 10_000,
+        });
+
+        const connectPromise = manager.connect();
+        await manager.stop();
+        ready.resolve(mockVoiceConnection);
+
+        await expect(connectPromise).rejects.toThrow(AudioManagerStateError);
+
+        expect(manager.state).toBe('stopped');
+        expect(manager.isConnected).toBe(false);
+        expect(jest.getTimerCount()).toBe(0);
+    });
+
+    it('keeps the latest connection when concurrent connects resolve out of order', async () => {
+        const firstReady = deferred<VoiceConnection>();
+        const secondReady = deferred<VoiceConnection>();
+        jest.mocked(joinVoiceChannel)
+            .mockReturnValueOnce(mockVoiceConnection)
+            .mockReturnValueOnce(mockSecondVoiceConnection);
+        jest.mocked(entersState)
+            .mockReturnValueOnce(firstReady.promise as unknown as MockedEntersStateReturn)
+            .mockReturnValueOnce(secondReady.promise as unknown as MockedEntersStateReturn);
+        const manager = new AudioManager({
+            connection: connectionOptions,
+            renewIntervalMs: false,
+        });
+
+        const firstConnect = manager.connect();
+        const secondConnect = manager.connect();
+        firstReady.resolve(mockVoiceConnection);
+        secondReady.resolve(mockSecondVoiceConnection);
+
+        await expect(firstConnect).rejects.toThrow(AudioManagerStateError);
+        await expect(secondConnect).resolves.toBeUndefined();
+
+        expect(manager.state).toBe('ready');
+        expect(manager.isConnected).toBe(true);
+        expect(mockConnection.destroy).toHaveBeenCalledTimes(1);
+        expect(mockSecondConnection.destroy).not.toHaveBeenCalled();
+    });
+
+    it('does not become ready when disposed during connection startup', async () => {
+        const ready = deferred<VoiceConnection>();
+        jest.mocked(entersState).mockReturnValueOnce(ready.promise as unknown as MockedEntersStateReturn);
+        const manager = new AudioManager({
+            connection: connectionOptions,
+            renewIntervalMs: false,
+        });
+
+        const connectPromise = manager.connect();
+        manager.dispose();
+        ready.resolve(mockVoiceConnection);
+
+        await expect(connectPromise).rejects.toThrow(AudioManagerStateError);
+
+        expect(manager.state).toBe('disposed');
+        expect(manager.isConnected).toBe(false);
+        expect(mockConnection.destroy).toHaveBeenCalledTimes(1);
+    });
+
     it('starts playback with the committed mp3 test file', async () => {
         const manager = new AudioManager({
             connection: connectionOptions,
@@ -144,6 +260,138 @@ 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('cleans up when audio resource creation fails', async () => {
+        const resourceError = new Error('resource failed');
+        jest.mocked(createAudioResource).mockImplementationOnce(() => {
+            throw resourceError;
+        });
+        const manager = new AudioManager({
+            connection: connectionOptions,
+            source: liveStreamSource,
+            renewIntervalMs: false,
+        });
+
+        await manager.connect();
+        await expect(manager.play()).rejects.toBe(resourceError);
+
+        expect(manager.state).toBe('ready');
+        expect(mockFfmpegHandle.stop).toHaveBeenCalledTimes(1);
+        expect(mockAudioPlayer.play).not.toHaveBeenCalled();
+    });
+
+    it('cleans up when the audio player rejects playback', async () => {
+        const playerError = new Error('player failed');
+        mockAudioPlayer.play.mockImplementationOnce(() => {
+            throw playerError;
+        });
+        const manager = new AudioManager({
+            connection: connectionOptions,
+            source: liveStreamSource,
+            renewIntervalMs: false,
+        });
+
+        await manager.connect();
+        await expect(manager.play()).rejects.toBe(playerError);
+
+        expect(manager.state).toBe('ready');
+        expect(mockFfmpegHandle.stop).toHaveBeenCalledTimes(1);
+        expect(mockAudioResource.playStream.destroy).toHaveBeenCalledTimes(1);
+    });
+
+    it('does not report playback when stopped before ffmpeg is ready', async () => {
+        const ready = deferred<void>();
+        jest.mocked(startFfmpeg).mockReturnValueOnce({
+            ...mockFfmpegHandle,
+            ready: ready.promise,
+        });
+        const manager = new AudioManager({
+            connection: connectionOptions,
+            source: liveStreamSource,
+            renewIntervalMs: false,
+        });
+
+        await manager.connect();
+        const playPromise = manager.play();
+        await manager.stop();
+        ready.resolve();
+
+        await expect(playPromise).rejects.toThrow(AudioManagerStateError);
+
+        expect(manager.state).toBe('stopped');
+        expect(mockAudioPlayer.play).not.toHaveBeenCalled();
+    });
+
+    it('does not report playback when disposed before ffmpeg is ready', async () => {
+        const ready = deferred<void>();
+        jest.mocked(startFfmpeg).mockReturnValueOnce({
+            ...mockFfmpegHandle,
+            ready: ready.promise,
+        });
+        const manager = new AudioManager({
+            connection: connectionOptions,
+            source: liveStreamSource,
+            renewIntervalMs: false,
+        });
+
+        await manager.connect();
+        const playPromise = manager.play();
+        manager.dispose();
+        ready.resolve();
+
+        await expect(playPromise).rejects.toThrow(AudioManagerStateError);
+
+        expect(manager.state).toBe('disposed');
+        expect(mockAudioPlayer.play).not.toHaveBeenCalled();
+    });
+
+    it('keeps only the latest concurrent playback', async () => {
+        const firstReady = deferred<void>();
+        const firstHandle = {
+            ...createMockFfmpegHandle(),
+            ready: firstReady.promise,
+        };
+        const secondHandle = createMockFfmpegHandle();
+        jest.mocked(startFfmpeg).mockReturnValueOnce(firstHandle).mockReturnValueOnce(secondHandle);
+        const manager = new AudioManager({
+            connection: connectionOptions,
+            source: liveStreamSource,
+            renewIntervalMs: false,
+        });
+
+        await manager.connect();
+        const firstPlay = manager.play();
+        const secondPlay = manager.play({ type: 'file', path: fileSourcePath });
+        firstReady.resolve();
+
+        await expect(firstPlay).rejects.toThrow(AudioManagerStateError);
+        await expect(secondPlay).resolves.toBeUndefined();
+
+        expect(manager.state).toBe('playing');
+        expect(mockAudioPlayer.play).toHaveBeenCalledTimes(1);
+        expect(firstHandle.stop).toHaveBeenCalledTimes(1);
+        expect(secondHandle.stop).not.toHaveBeenCalled();
+    });
+
     it('replaces active playback when a new source is played', async () => {
         const manager = new AudioManager({
             connection: connectionOptions,
@@ -233,6 +481,12 @@ describe('AudioManager', () => {
 
         expect(() => manager.setVolume(-1)).toThrow(AudioManagerConfigError);
         expect(() => manager.setVolume(101)).toThrow(AudioManagerConfigError);
+        expect(() => manager.setVolume(Number.NaN)).toThrow(AudioManagerConfigError);
+        expect(() => manager.setVolume(Number.POSITIVE_INFINITY)).toThrow(AudioManagerConfigError);
+        expect(() => manager.setVolume(Number.NEGATIVE_INFINITY)).toThrow(AudioManagerConfigError);
+        expect(() => manager.setVolume(0)).not.toThrow();
+        expect(() => manager.setVolume(42)).not.toThrow();
+        expect(() => manager.setVolume(100)).not.toThrow();
     });
 
     it('rejects volume changes before any resource exists', () => {
@@ -281,6 +535,20 @@ describe('AudioManager', () => {
         expect(manager.state).toBe('stopped');
     });
 
+    it('rejects pause and resume after stop', async () => {
+        const manager = new AudioManager({
+            connection: connectionOptions,
+            source: liveStreamSource,
+            renewIntervalMs: false,
+        });
+
+        await manager.start();
+        await manager.stop();
+
+        expect(() => manager.pause()).toThrow(AudioManagerStateError);
+        expect(() => manager.resume()).toThrow(AudioManagerStateError);
+    });
+
     it('restarts playback when the renewal timer fires', async () => {
         jest.useFakeTimers();
 
@@ -298,6 +566,27 @@ describe('AudioManager', () => {
         expect(startSpy).toHaveBeenCalledTimes(1);
     });
 
+    it('cleans up when renewal restart fails', async () => {
+        jest.useFakeTimers();
+
+        const manager = new AudioManager({
+            connection: connectionOptions,
+            source: liveStreamSource,
+            renewIntervalMs: 10_000,
+        });
+        const startSpy = jest.spyOn(manager, 'start').mockRejectedValue(new Error('renewal failed'));
+
+        await manager.connect();
+        jest.advanceTimersByTime(10_000);
+        await Promise.resolve();
+
+        expect(startSpy).toHaveBeenCalledTimes(1);
+        expect(mockAudioPlayer.stop).toHaveBeenCalledWith(true);
+        expect(mockConnection.destroy).toHaveBeenCalled();
+        expect(manager.state).toBe('stopped');
+        expect(jest.getTimerCount()).toBe(0);
+    });
+
     it('clears existing renewal timer before reconnecting', async () => {
         jest.useFakeTimers();
 

tests/ffmpeg.test.ts

@@ -1,6 +1,8 @@
 import { jest, describe, beforeEach, afterEach, it, expect } from '@jest/globals';
 import { spawn } from 'node:child_process';
+import type { ChildProcess } from 'node:child_process';
 
+import { FfmpegProcessError } from '../src';
 import { resolveFfmpegExecutable, startFfmpeg } from '../src/ffmpeg';
 
 jest.mock('node:child_process', () => ({
@@ -12,12 +14,16 @@ 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 +35,16 @@ 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,
@@ -43,6 +53,26 @@ function createMockChildProcess(): MockChildProcess {
     };
 }
 
+function mockSpawnReturn(childProcess: MockChildProcess): void {
+    mockSpawn.mockReturnValue(childProcess as unknown as ChildProcess);
+}
+
+function getProcessHandler(childProcess: MockChildProcess, eventName: string): (...args: unknown[]) => void {
+    return childProcess.once.mock.calls.find(([event]) => event === eventName)?.[1] as (...args: unknown[]) => void;
+}
+
+function getStdoutHandler(childProcess: MockChildProcess, eventName: string): (...args: unknown[]) => void {
+    return childProcess.stdout.once.mock.calls.find(([event]) => event === eventName)?.[1] as (
+        ...args: unknown[]
+    ) => void;
+}
+
+function getStderrHandler(childProcess: MockChildProcess, eventName: string): (...args: unknown[]) => void {
+    return childProcess.stderr.on.mock.calls.find(([event]) => event === eventName)?.[1] as (
+        ...args: unknown[]
+    ) => void;
+}
+
 describe('ffmpeg helpers', () => {
     beforeEach(() => {
         jest.clearAllMocks();
@@ -63,7 +93,7 @@ describe('ffmpeg helpers', () => {
 
     it('spawns ffmpeg with the default argument set', () => {
         const childProcess = createMockChildProcess();
-        mockSpawn.mockReturnValue(childProcess);
+        mockSpawnReturn(childProcess);
 
         startFfmpeg('https://synradiode.stream.laut.fm/synradiode');
 
@@ -88,12 +118,70 @@ 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();
+        mockSpawnReturn(childProcess);
+
+        const handle = startFfmpeg('tests/audio.mp3');
+        const errorHandler = getProcessHandler(childProcess, 'error');
+
+        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();
+        mockSpawnReturn(childProcess);
+
+        const handle = startFfmpeg('tests/audio.mp3');
+        const stderrHandler = getStderrHandler(childProcess, 'data');
+        const exitHandler = getProcessHandler(childProcess, 'exit');
+
+        stderrHandler('invalid input');
+        exitHandler(1, null);
+
+        await expect(handle.ready).rejects.toThrow('invalid input');
+    });
+
+    it('keeps the useful tail of long ffmpeg stderr output', async () => {
+        const childProcess = createMockChildProcess();
+        mockSpawnReturn(childProcess);
+
+        const handle = startFfmpeg('tests/audio.mp3');
+        const stderrHandler = getStderrHandler(childProcess, 'data');
+        const exitHandler = getProcessHandler(childProcess, 'exit');
+
+        stderrHandler(`${'x'.repeat(5_000)}final diagnostic`);
+        exitHandler(1, null);
+
+        await expect(handle.ready).rejects.toThrow('final diagnostic');
+    });
+
+    it('keeps readiness resolved when ffmpeg exits after producing audio', async () => {
+        const childProcess = createMockChildProcess();
+        mockSpawnReturn(childProcess);
+
+        const handle = startFfmpeg('tests/audio.mp3');
+        const readableHandler = getStdoutHandler(childProcess, 'readable');
+        const exitHandler = getProcessHandler(childProcess, 'exit');
+
+        readableHandler();
+        exitHandler(1, null);
+
+        await expect(handle.ready).resolves.toBeUndefined();
+    });
+
     it('uses custom executable and argument overrides when provided', () => {
         const childProcess = createMockChildProcess();
-        mockSpawn.mockReturnValue(childProcess);
+        mockSpawnReturn(childProcess);
 
         startFfmpeg('tests/audio.mp3', {
             executablePath: '/custom/ffmpeg',
@@ -111,7 +199,7 @@ describe('ffmpeg helpers', () => {
     it('stops a running child process and schedules a force kill fallback', () => {
         jest.useFakeTimers();
         const childProcess = createMockChildProcess();
-        mockSpawn.mockReturnValue(childProcess);
+        mockSpawnReturn(childProcess);
 
         const handle = startFfmpeg('tests/audio.mp3');
         handle.stop();
@@ -129,7 +217,7 @@ describe('ffmpeg helpers', () => {
     it('does not signal a process that already exited', () => {
         const childProcess = createMockChildProcess();
         childProcess.exitCode = 0;
-        mockSpawn.mockReturnValue(childProcess);
+        mockSpawnReturn(childProcess);
 
         const handle = startFfmpeg('tests/audio.mp3');
         handle.stop();