Update Dockerfile

Dockerfile

@@ -13,6 +13,10 @@ RUN cp -f ./custom-imagemagick-policy.yml /etc/ImageMagick-6/policy.xml
 RUN sed -i 's/none/read,write/g' /etc/ImageMagick-6/policy.xml 
 ##安装imagemagic
 
+#设置ffmpeg环境变量
+RUN apt install -y ffmpeg
+ENV FFMPEG_BINARY=/usr/bin/ffmpeg
+
 RUN pip install -U pip