How to: Strongly recommended
* [**ffmpeg** and **ffprobe**](https://www.ffmpeg.org) - Required for [merging separate video and audio files](#format-selection), as well as for various [post-processing](#post-processing-options) tasks. License [depends on the build](https://www.ffmpeg.org/legal.html)

    There are bugs in ffmpeg that cause various issues when used alongside yt-dlp. Since ffmpeg is such an important dependency, we provide [custom builds](https://github.com/yt-dlp/FFmpeg-Builds#ffmpeg-static-auto-builds) with patches for some of these issues at [yt-dlp/FFmpeg-Builds](https://github.com/yt-dlp/FFmpeg-Builds). See [the readme](https://github.com/yt-dlp/FFmpeg-Builds#patches-applied) for details on the specific issues solved by these builds

    **Important**: What you need is ffmpeg *binary*, **NOT** [the Python package of the same name](https://pypi.org/project/ffmpeg)

* [**yt-dlp-ejs**](https://github.com/yt-dlp/ejs) - Required for deciphering YouTube n/sig values. Licensed under [Unlicense](https://github.com/yt-dlp/ejs/blob/main/LICENSE), bundles [MIT](https://github.com/davidbonnet/astring/blob/main/LICENSE) and [ISC](https://github.com/meriyah/meriyah/blob/main/LICENSE.md) components.

    A JavaScript runtime/engine like [**deno**](https://deno.land) (recommended), [**node.js**](https://nodejs.org), [**bun**](https://bun.sh), or [**QuickJS**](https://bellard.org/quickjs/) is also required to run yt-dlp-ejs. See [the wiki](https://github.com/yt-dlp/yt-dlp/wiki/EJS).