diff --git a/utils/testdata.sh b/utils/testdata.sh
index d0c1072..572ed64 100755
--- a/utils/testdata.sh
+++ b/utils/testdata.sh
@@ -6,8 +6,8 @@ create_file() {
 
 rm -rf testdata
 mkdir testdata
-create_file "a.mp4"
+ffmpeg -f lavfi -i testsrc -t 30 -pix_fmt yuv420p testdata/a.mp4
 create_file "a.gif"
 create_file "b.gif"
 create_file "b.jpeg"
-create_file "c.mp4"
+ffmpeg -f lavfi -i testsrc -t 30 -pix_fmt yuv420p testdata/b.mp4