diff --git a/Dockerfile b/Dockerfile
index 4d26b473..c6587650 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -931,7 +931,7 @@ ENV FIREFOX_VERSION="${FF_VER}" \
   FIREFOX="true" \
   MULTINODE="false" \
   FFMPEG_FRAME_RATE=10 \
-  FFMPEG_CODEC_ARGS="-crf 0 -preset ultrafast -qp 0" \
+  FFMPEG_CODEC_ARGS="-crf 0 -preset ultrafast -qp 0 -pix_fmt yuv420p" \
   FFMPEG_FINAL_CRF=0 \
   FFMPEG_DRAW_MOUSE=1 \
   VIDEO_TMP_FILE_EXTENSION="mkv" \
diff --git a/README.md b/README.md
index cb1a8fe8..918a54d5 100644
--- a/README.md
+++ b/README.md
@@ -202,7 +202,7 @@ Once your tests are done you can either manually stop the recording via `docker
 Relevant up-to-date environment variables to customize it are at the Dockerfile, below a possibly outdated list of settings:
 
     FFMPEG_FRAME_RATE=10
-    FFMPEG_CODEC_ARGS="-crf 0 -preset ultrafast -qp 0"
+    FFMPEG_CODEC_ARGS="-crf 0 -preset ultrafast -qp 0 -pix_fmt yuv420p"
     FFMPEG_FINAL_CRF=0
     FFMPEG_DRAW_MOUSE=1
     VIDEO_TMP_FILE_EXTENSION="mkv"