diff --git a/.gitignore b/.gitignore
index 3821511..14b30a9 100644
--- a/.gitignore
+++ b/.gitignore
@@ -108,3 +108,4 @@ dist
 vendor
 test/*.webm
 .idea/
+scenarios/
diff --git a/package.json b/package.json
index 4db0a37..3a804c5 100644
--- a/package.json
+++ b/package.json
@@ -13,11 +13,14 @@
     "pridepack"
   ],
   "devDependencies": {
+    "@types/dotenv": "^8.2.0",
     "@types/node": "^18.14.1",
+    "dotenv": "^16.0.3",
     "eslint": "^8.35.0",
     "eslint-config-lxsmnsyc": "^0.5.0",
     "pridepack": "2.4.2",
     "tslib": "^2.5.0",
+    "tsx": "^3.12.6",
     "typescript": "^4.9.5",
     "vitest": "^0.28.1"
   },
@@ -30,7 +33,8 @@
     "watch": "pridepack watch",
     "start": "pridepack start",
     "dev": "pridepack dev",
-    "test": "vitest"
+    "test": "vitest",
+    "tsx": "tsx"
   },
   "private": false,
   "description": "Clip YouTube videos.",
diff --git a/src/index.ts b/src/index.ts
index b19b158..1a883ae 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,53 +1,173 @@
 import { spawnSync } from 'child_process';
 import { unlinkSync, readFileSync } from 'fs';
+import { EventEmitter } from 'events';
 
 export enum VideoType {
   YOUTUBE = 'youtube',
 }
 
 interface ClipVideoBaseParams {
-  url: string,
-  start: number | string,
-  end: number | string,
+  url: string;
+  start?: number | string;
+  end?: number | string;
 }
 
 interface ClipYouTubeVideoParams extends ClipVideoBaseParams {
   downloaderExecutablePath?: string;
+  postprocessorExecutablePath?: string;
 }
 
 interface ClipVideoParams extends ClipYouTubeVideoParams {
   type: VideoType,
 }
 
-const clipYouTubeVideo = (params: ClipYouTubeVideoParams) => {
-  if (!params.downloaderExecutablePath) {
-    throw new Error('Downloader not found.');
+const convertSecondsToDuration = (s: number) => {
+  const milliseconds = (s - Math.floor(s)) * 1000;
+  const seconds = s % 60;
+  const minutes = Math.floor(s / 60) % 60;
+  const hours = Math.floor(s / 3600);
+  const sss = milliseconds.toString().padStart(3, '0');
+  const ss = seconds.toString().padStart(2, '0');
+  const mm = minutes.toString().padStart(2, '0');
+  const hh = hours.toString().padStart(2, '0');
+  return `${hh}:${mm}:${ss}.${sss}`;
+};
+
+const convertDurationToSeconds = (d: string) => {
+  const [hh, mm, ss] = d.split(':');
+  return (Number(hh) * 3600) + (Number(mm) * 60) + Number(ss);
+};
+
+export interface ClipEventEmitter extends EventEmitter {
+  process(): void;
+}
+
+class YouTubeVideoClipEventEmitter extends EventEmitter implements ClipEventEmitter {
+  constructor(private readonly params: ClipYouTubeVideoParams) {
+    super();
   }
-  spawnSync(
-    params.downloaderExecutablePath,
-    [
-      '--postprocessor-args',
-      `-ss ${params.start.toString()} -to ${params.end.toString()}`,
-      '-o',
+
+  process() {
+    if (!this.params.downloaderExecutablePath) {
+      this.emit('error', new Error('Downloader not found.'));
+      this.emit('end', null);
+      return;
+    }
+
+    if (!this.params.postprocessorExecutablePath) {
+      this.emit('error', new Error('ffmpeg not found.'));
+      this.emit('end', null);
+      return;
+    }
+
+    const downloadArgs = [
+      '--youtube-skip-dash-manifest',
+      '-f', 'bestvideo+bestaudio',
+      '-g', this.params.url,
+    ];
+    this.emit('process', {
+      type: 'download',
+      phase: 'start',
+      command: `${this.params.downloaderExecutablePath} ${downloadArgs.join(' ')}`,
+    });
+    const downloaderProcess = spawnSync(this.params.downloaderExecutablePath, downloadArgs);
+    if (downloaderProcess.error) {
+      this.emit('error', new Error('Downloader error.', { cause: downloaderProcess.error }));
+      this.emit('end', null);
+      return;
+    }
+
+    const [videoUrlStream, audioUrlStream] = downloaderProcess.stdout.toString('utf-8').split('\n');
+    this.emit('process', {
+      type: 'download',
+      phase: 'success',
+      streamUrls: {
+        video: [videoUrlStream],
+        audio: [audioUrlStream],
+      },
+    });
+
+    let startSeconds: number;
+    if (typeof this.params.start === 'undefined') {
+      startSeconds = 0;
+    } else if (typeof this.params.start === 'string') {
+      startSeconds = convertDurationToSeconds(this.params.start);
+    } else {
+      startSeconds = this.params.start;
+    }
+
+    const ffmpegProcessVideoStreamArgs = [
+      '-ss', (this.params.start ?? '00:00:00').toString(),
+      '-i', videoUrlStream,
+    ];
+
+    const ffmpegProcessAudioStreamArgs = [
+      '-ss', (this.params.start ?? '00:00:00').toString(),
+      '-i', audioUrlStream,
+    ];
+
+    if (typeof this.params.end !== 'undefined') {
+      // -to flag is broken on video stream in ffmpeg.....
+      const endSeconds = (
+        typeof this.params.end === 'string'
+          ? convertDurationToSeconds(this.params.end)
+          : this.params.end
+      );
+
+      const difference = endSeconds - startSeconds;
+      const clipDuration = convertSecondsToDuration(difference);
+
+      ffmpegProcessVideoStreamArgs.push('-t');
+      ffmpegProcessVideoStreamArgs.push(clipDuration);
+
+      ffmpegProcessAudioStreamArgs.push('-t');
+      ffmpegProcessAudioStreamArgs.push(clipDuration);
+    }
+
+    const ffmpegProcessArgs = [
+      ...ffmpegProcessVideoStreamArgs,
+      ...ffmpegProcessAudioStreamArgs,
+      '-map', '0:v',
+      '-map', '1:a',
       'output.webm',
-      params.url,
-    ],
-  );
-  const output = readFileSync('output.webm');
-  unlinkSync('output.webm');
-  return output;
-};
+    ];
+    this.emit('process', {
+      type: 'postprocess',
+      phase: 'start',
+      command: `${this.params.postprocessorExecutablePath} ${ffmpegProcessArgs.join(' ')}`,
+    });
+    const ffmpegProcess = spawnSync(this.params.postprocessorExecutablePath, ffmpegProcessArgs);
+    if (ffmpegProcess.error) {
+      this.emit('error', new Error('ffmpeg error.', { cause: ffmpegProcess.error }));
+      this.emit('end');
+      return;
+    }
+    const output = readFileSync('output.webm');
+    unlinkSync('output.webm');
+    this.emit('process', {
+      type: 'postprocess',
+      phase: 'success',
+      output,
+    });
+    this.emit('end');
+  }
+}
 
-export const clipVideo = (params: ClipVideoParams) => {
+export const createVideoClipper = (params: ClipVideoParams) => {
   const {
-    type: videoType, url, start, end,
+    type: videoType,
+    url,
+    start,
+    end,
     downloaderExecutablePath,
+    postprocessorExecutablePath,
   } = params;
 
   switch (videoType as string) {
     case VideoType.YOUTUBE:
-      return clipYouTubeVideo({
+      return new YouTubeVideoClipEventEmitter({
         downloaderExecutablePath,
+        postprocessorExecutablePath,
         url,
         start,
         end,
diff --git a/test/index.test.ts b/test/index.test.ts
index 645bf3f..60b08ea 100644
--- a/test/index.test.ts
+++ b/test/index.test.ts
@@ -1,9 +1,10 @@
 import {
-  describe, it, expect, vi, beforeEach, Mock,
+  describe, it, expect, vi, beforeEach, Mock, afterEach,
 } from 'vitest';
 import { spawnSync } from 'child_process';
 import { readFileSync, unlinkSync } from 'fs';
-import * as youtubeClipCore from '../src';
+import * as webVideoClipCore from '../src';
+import { ClipEventEmitter } from '../src';
 
 vi.mock('child_process', () => ({
   spawnSync: vi.fn(),
@@ -14,44 +15,92 @@ vi.mock('fs', () => ({
   unlinkSync: vi.fn(),
 }));
 
-describe('clipVideo', () => {
+describe('createVideoClipper', () => {
   beforeEach(() => {
     (readFileSync as Mock).mockReturnValueOnce(Buffer.from(''));
   });
 
-  it('calls the downloader function', () => {
-    youtubeClipCore.clipVideo({
+  let clipper: ClipEventEmitter;
+  beforeEach(() => {
+    clipper = webVideoClipCore.createVideoClipper({
       downloaderExecutablePath: 'yt-dlp',
-      type: youtubeClipCore.VideoType.YOUTUBE,
+      postprocessorExecutablePath: 'ffmpeg',
+      type: webVideoClipCore.VideoType.YOUTUBE,
       url: 'https://www.youtube.com/watch?v=BaW_jenozKc',
       start: 0,
       end: 0,
     });
+  });
 
-    expect(spawnSync).toBeCalledWith('yt-dlp', expect.anything());
+  afterEach(() => {
+    (spawnSync as Mock).mockReset();
   });
 
-  it('calls the buffer extract function', () => {
-    youtubeClipCore.clipVideo({
-      downloaderExecutablePath: 'yt-dlp',
-      type: youtubeClipCore.VideoType.YOUTUBE,
-      url: 'https://www.youtube.com/watch?v=BaW_jenozKc',
-      start: 0,
-      end: 0,
+  it('calls the downloader function', () => new Promise((done) => {
+    (spawnSync as Mock)
+      .mockReturnValueOnce({ stdout: Buffer.from('') })
+      .mockReturnValueOnce({});
+
+    clipper.on('end', done);
+    clipper.process();
+    expect(spawnSync).nthCalledWith(1, 'yt-dlp', expect.anything());
+  }));
+
+  it('emits downloader errors', () => new Promise((done) => {
+    const causeError = new Error('generic downloader message');
+    (spawnSync as Mock)
+      .mockReturnValueOnce({ error: causeError })
+      .mockReturnValueOnce({});
+
+    clipper.on('error', (err: Error) => {
+      expect(err.cause).toHaveProperty('message', causeError.message);
     });
+    clipper.on('end', done);
+    clipper.process();
+  }));
 
-    expect(readFileSync).toBeCalled();
-  });
+  it('calls the postprocess function', () => new Promise((done) => {
+    (spawnSync as Mock)
+      .mockReturnValueOnce({ stdout: Buffer.from('') })
+      .mockReturnValueOnce({});
 
-  it('calls the cleanup function', () => {
-    youtubeClipCore.clipVideo({
-      downloaderExecutablePath: 'yt-dlp',
-      type: youtubeClipCore.VideoType.YOUTUBE,
-      url: 'https://www.youtube.com/watch?v=BaW_jenozKc',
-      start: 0,
-      end: 0,
+    clipper.on('end', done);
+    clipper.process();
+    expect(spawnSync).nthCalledWith(2, 'ffmpeg', expect.anything());
+  }));
+
+  it('emits postprocess errors', () => new Promise((done) => {
+    const causeError = new Error('generic postprocessor message');
+    (spawnSync as Mock)
+      .mockReturnValueOnce({ stdout: Buffer.from('') })
+      .mockReturnValueOnce({ error: causeError });
+
+    clipper.on('error', (err: Error) => {
+      expect(err.cause).toHaveProperty('message', causeError.message);
     });
+    clipper.on('end', done);
+    clipper.process();
+  }));
+
+  it('calls the buffer extract function', () => new Promise((done) => {
+    (spawnSync as Mock)
+      .mockReturnValueOnce({ stdout: Buffer.from('') })
+      .mockReturnValueOnce({});
+
+    clipper.on('end', done);
+    clipper.process();
+
+    expect(readFileSync).toBeCalled();
+  }));
+
+  it('calls the cleanup function', () => new Promise((done) => {
+    (spawnSync as Mock)
+      .mockReturnValueOnce({ stdout: Buffer.from('') })
+      .mockReturnValueOnce({});
+
+    clipper.on('end', done);
+    clipper.process();
 
     expect(unlinkSync).toBeCalled();
-  });
+  }));
 });
diff --git a/test/try-service.js b/test/try-service.js
deleted file mode 100644
index a8cc111..0000000
--- a/test/try-service.js
+++ /dev/null
@@ -1,15 +0,0 @@
-const { clipVideo, VideoType } = require('../dist/cjs/development');
-const fs = require('fs');
-const dotenv = require('dotenv');
-
-dotenv.config();
-
-const clippedVideoBuffer = clipVideo({
-  downloaderExecutablePath: process.env.YOUTUBE_DOWNLOADER_EXECUTABLE_PATH,
-  type: VideoType.YOUTUBE,
-  url: 'https://www.youtube.com/watch?v=BaW_jenozKc',
-  start: 0,
-  end: 1,
-});
-
-fs.writeFileSync('output.webm', clippedVideoBuffer);
diff --git a/yarn.lock b/yarn.lock
index 7cf2ecd..f355bd7 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -233,6 +233,30 @@
     "@babel/helper-validator-identifier" "^7.19.1"
     to-fast-properties "^2.0.0"
 
+"@esbuild-kit/cjs-loader@^2.4.2":
+  version "2.4.2"
+  resolved "https://registry.yarnpkg.com/@esbuild-kit/cjs-loader/-/cjs-loader-2.4.2.tgz#cb4dde00fbf744a68c4f20162ea15a8242d0fa54"
+  integrity sha512-BDXFbYOJzT/NBEtp71cvsrGPwGAMGRB/349rwKuoxNSiKjPraNNnlK6MIIabViCjqZugu6j+xeMDlEkWdHHJSg==
+  dependencies:
+    "@esbuild-kit/core-utils" "^3.0.0"
+    get-tsconfig "^4.4.0"
+
+"@esbuild-kit/core-utils@^3.0.0":
+  version "3.1.0"
+  resolved "https://registry.yarnpkg.com/@esbuild-kit/core-utils/-/core-utils-3.1.0.tgz#49945d533dbd5e1b7620aa0fc522c15e6ec089c5"
+  integrity sha512-Uuk8RpCg/7fdHSceR1M6XbSZFSuMrxcePFuGgyvsBn+u339dk5OeL4jv2EojwTN2st/unJGsVm4qHWjWNmJ/tw==
+  dependencies:
+    esbuild "~0.17.6"
+    source-map-support "^0.5.21"
+
+"@esbuild-kit/esm-loader@^2.5.5":
+  version "2.5.5"
+  resolved "https://registry.yarnpkg.com/@esbuild-kit/esm-loader/-/esm-loader-2.5.5.tgz#b82da14fcee3fc1d219869756c06f43f67d1ca71"
+  integrity sha512-Qwfvj/qoPbClxCRNuac1Du01r9gvNOT+pMYtJDapfB1eoGN1YlJ1BixLyL9WVENRx5RXgNLdfYdx/CuswlGhMw==
+  dependencies:
+    "@esbuild-kit/core-utils" "^3.0.0"
+    get-tsconfig "^4.4.0"
+
 "@esbuild/android-arm64@0.17.12":
   version "0.17.12"
   resolved "https://registry.yarnpkg.com/@esbuild/android-arm64/-/android-arm64-0.17.12.tgz#15a8e2b407d03989b899e325151dc2e96d19c620"
@@ -508,6 +532,13 @@
   resolved "https://registry.yarnpkg.com/@types/chai/-/chai-4.3.4.tgz#e913e8175db8307d78b4e8fa690408ba6b65dee4"
   integrity sha512-KnRanxnpfpjUTqTCXslZSEdLfXExwgNxYPdiO2WGUj8+HDjFi8R3k5RVKPeSCzLjCcshCAtVO2QBbVuAV4kTnw==
 
+"@types/dotenv@^8.2.0":
+  version "8.2.0"
+  resolved "https://registry.yarnpkg.com/@types/dotenv/-/dotenv-8.2.0.tgz#5cd64710c3c98e82d9d15844375a33bf1b45d053"
+  integrity sha512-ylSC9GhfRH7m1EUXBXofhgx4lUWmFeQDINW5oLuS+gxWdfUeW4zJdeVTYVkexEW+e2VUvlZR2kGnGGipAWR7kw==
+  dependencies:
+    dotenv "*"
+
 "@types/json-schema@^7.0.9":
   version "7.0.11"
   resolved "https://registry.yarnpkg.com/@types/json-schema/-/json-schema-7.0.11.tgz#d421b6c527a3037f7c84433fd2c4229e016863d3"
@@ -1180,7 +1211,7 @@ dot-prop@^5.2.0:
   dependencies:
     is-obj "^2.0.0"
 
-dotenv@^16.0.3:
+dotenv@*, dotenv@^16.0.3:
   version "16.0.3"
   resolved "https://registry.yarnpkg.com/dotenv/-/dotenv-16.0.3.tgz#115aec42bac5053db3c456db30cc243a5a836a07"
   integrity sha512-7GO6HghkA5fYG9TYnNxi14/7K9f5occMlp3zXAuSxn7CKCxt9xbNWG7yF8hTCSUchlfWSe3uLmlPfigevRItzQ==
@@ -1293,7 +1324,7 @@ es-to-primitive@^1.2.1:
     is-date-object "^1.0.1"
     is-symbol "^1.0.2"
 
-esbuild@^0.17.4, esbuild@^0.17.5:
+esbuild@^0.17.4, esbuild@^0.17.5, esbuild@~0.17.6:
   version "0.17.12"
   resolved "https://registry.yarnpkg.com/esbuild/-/esbuild-0.17.12.tgz#2ad7523bf1bc01881e9d904bc04e693bd3bdcf2f"
   integrity sha512-bX/zHl7Gn2CpQwcMtRogTTBf9l1nl+H6R8nUbjk+RuKqAE3+8FDulLA+pHvX7aA7Xe07Iwa+CWvy9I8Y2qqPKQ==
@@ -1807,7 +1838,7 @@ get-symbol-description@^1.0.0:
     call-bind "^1.0.2"
     get-intrinsic "^1.1.1"
 
-get-tsconfig@^4.2.0:
+get-tsconfig@^4.2.0, get-tsconfig@^4.4.0:
   version "4.4.0"
   resolved "https://registry.yarnpkg.com/get-tsconfig/-/get-tsconfig-4.4.0.tgz#64eee64596668a81b8fce18403f94f245ee0d4e5"
   integrity sha512-0Gdjo/9+FzsYhXCEFueo2aY1z1tpXrxWZzP7k8ul9qt1U5o8rYJwTJYmaeHdrVosYIVYkOy2iwCJ9FdpocJhPQ==
@@ -3240,6 +3271,17 @@ tsutils@^3.21.0:
   dependencies:
     tslib "^1.8.1"
 
+tsx@^3.12.6:
+  version "3.12.6"
+  resolved "https://registry.yarnpkg.com/tsx/-/tsx-3.12.6.tgz#36b3693e48b8392da374487190972c7b80e433b4"
+  integrity sha512-q93WgS3lBdHlPgS0h1i+87Pt6n9K/qULIMNYZo07nSeu2z5QE2CellcAZfofVXBo2tQg9av2ZcRMQ2S2i5oadQ==
+  dependencies:
+    "@esbuild-kit/cjs-loader" "^2.4.2"
+    "@esbuild-kit/core-utils" "^3.0.0"
+    "@esbuild-kit/esm-loader" "^2.5.5"
+  optionalDependencies:
+    fsevents "~2.3.2"
+
 type-check@^0.4.0, type-check@~0.4.0:
   version "0.4.0"
   resolved "https://registry.yarnpkg.com/type-check/-/type-check-0.4.0.tgz#07b8203bfa7056c0657050e3ccd2c37730bab8f1"