diff --git a/capture-full-replay.sh b/capture-full-replay.sh
index 5a235f7..b47f77e 100755
--- a/capture-full-replay.sh
+++ b/capture-full-replay.sh
@@ -23,6 +23,7 @@ docker run --rm -d --name=grid -p 4444:24444 -p 5920:25900 \
   -e SCREEN_WIDTH=1080 -e SCREEN_HEIGHT=720 \
   -e FFMPEG_DRAW_MOUSE=0 \
   -e FFMPEG_FRAME_RATE=24 \
+  -e VIDEO_FILE_EXTENSION="mkv" \
   elgalu/selenium
 
 docker exec grid wait_all_done 30s