Add ffmpeg

dockerfile

@@ -15,7 +15,8 @@ ARG TARGETARCH
 
 ARG DEPENDENCIES="  \
     ca-certificates \
-    libsox-dev"
+    libsox-dev \
+    ffmpeg"
 
 RUN --mount=type=cache,target=/var/cache/apt,sharing=locked \
     --mount=type=cache,target=/var/lib/apt,sharing=locked \