diff --git a/docs/setup.en.md b/docs/setup.en.md
index 25cad9204..741c597d6 100644
--- a/docs/setup.en.md
+++ b/docs/setup.en.md
@@ -29,6 +29,7 @@ Please install and setup these softwares:
 * [Redis](https://redis.io/)
   * Redis is optional, but we strongly recommended to install it
 * [Elasticsearch](https://www.elastic.co/) - required to enable the search feature
+* ffmpeg
 
 *3.* Setup MongoDB
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diff --git a/docs/setup.fr.md b/docs/setup.fr.md
index 01fc810a3..c7005e68d 100644
--- a/docs/setup.fr.md
+++ b/docs/setup.fr.md
@@ -29,6 +29,7 @@ Installez les paquets suivants :
 * [Redis](https://redis.io/)
   * Redis est optionnel mais nous vous recommandons vivement de l'installer
 * [Elasticsearch](https://www.elastic.co/) - requis pour pouvoir activer la fonctionnalité de recherche
+* ffmpeg
 
 *3.* Paramètrage de MongoDB
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diff --git a/docs/setup.ja.md b/docs/setup.ja.md
index 46e608aa9..4598acc20 100644
--- a/docs/setup.ja.md
+++ b/docs/setup.ja.md
@@ -35,6 +35,7 @@ adduser --disabled-password --disabled-login misskey
 		* Twitter連携
 * [Elasticsearch](https://www.elastic.co/)
 	* 検索機能を有効にするためにはインストールが必要です。
+* ffmpeg
 
 *3.* MongoDBの設定
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