Use non-deprecated frames option.

Pointed out by JP Mens.

llgal.org

@@ -80,11 +80,11 @@ hack around that a bit.
 First we use ~ffmpeg~ to create the thumbnails:
 #+begin_src shell
   for i in *.mp4; do
-      ffmpeg -ss 1 -i ${i} -vframes 1 -vf "scale=240:-1" \
+      ffmpeg -ss 1 -i ${i} -frames:v 1 -vf "scale=240:-1" \
              .llgal/my_thump_${i}.jpg
   done
 #+end_src
-We grab one frame (=-vframes 1=), one second into the video (=-ss
+We grab one frame (=-frames:v 1=), one second into the video (=-ss
 1=), and scale it to 240 pixels wide while keeping the aspect ratio
 (=-vf "scale=240:-1"=). We store the thumbnail in the ~.llgal~
 sub-directory, where ~llgal~ stores its own thumbnails and scaled