fix: embed the animation as a GIF instead of a <video> tag

README.md

@@ -238,10 +238,11 @@ License: GNU General Public License v3.0
 options:
   -h, --help            show this help message and exit
   -b, --bitrate BITRATE
-                        bitrate (in kbps) of the encoded video (default: 1800)
+                        bitrate (in kbps) of the encoded MP4 video, ignored
+                        for GIF output (default: 1800)
   -f, --outfile OUTFILE
-                        name of the output MP4 file; if not set the animation
-                        is displayed interactively instead
+                        name of the output file (.mp4 or .gif); if not set the
+                        animation is displayed interactively instead
   --fps FPS             frames per second of the encoded video (default: 25)
   --hold HOLD           seconds to hold the last frame at the end of the
                         animation (default: 2.0)
@@ -257,17 +258,19 @@ examples:
   hadcrut5_animate.py --global
   hadcrut5_animate.py --period "1880-1920"
   hadcrut5_animate.py --period "1880-1920" --outfile HadCRUT5-1880-1920-animation.mp4
+  hadcrut5_animate.py --period "1880-1920" --outfile HadCRUT5-1880-1920-animation.gif
   hadcrut5_animate.py --fps 30 --hold 5 --outfile HadCRUT5-animation.mp4
 ```
 
-This script requires `ffmpeg` to be installed, and reveals the selected regions year by year instead of drawing the
-whole time series at once. Without `--outfile` the animation is displayed interactively; with it, the animation is
-encoded to an MP4 file.
+This script reveals the selected regions year by year instead of drawing the whole time series at once. Without
+`--outfile` the animation is displayed interactively. An `.mp4` output requires `ffmpeg` to be installed; a `.gif`
+output only needs Pillow (already a Matplotlib dependency). GitHub's Markdown renderer strips `<video>` tags for
+repo-hosted files, so the GIF format is what's embedded below.
 
 ```
-$ ./hadcrut5_animate.py --period "1880-1920" --outfile plots/HadCRUT5-1880-1920-animation.mp4
+$ ./hadcrut5_animate.py --period "1880-1920" --outfile plots/HadCRUT5-1880-1920-animation.gif
 ```
-<video src="plots/HadCRUT5-1880-1920-animation.mp4" controls loop autoplay muted playsinline></video>
+![HadCRUT5 animated plot of the temperature anomalies related to 1880-1920](plots/HadCRUT5-1880-1920-animation.gif)
 
 # License
 

hadcrut5_animate.py

@@ -52,6 +52,7 @@ def parse_args() -> argparse.Namespace:
         "%(prog)s --global",
         '%(prog)s --period "1880-1920"',
         '%(prog)s --period "1880-1920" --outfile HadCRUT5-1880-1920-animation.mp4',
+        '%(prog)s --period "1880-1920" --outfile HadCRUT5-1880-1920-animation.gif',
         "%(prog)s --fps 30 --hold 5 --outfile HadCRUT5-animation.mp4",
     ]
 
@@ -63,15 +64,16 @@ def parse_args() -> argparse.Namespace:
         dest="bitrate",
         default=1800,
         type=int,
-        help="bitrate (in kbps) of the encoded video (default: 1800)",
+        help="bitrate (in kbps) of the encoded MP4 video, ignored for GIF "
+        "output (default: 1800)",
     )
     parser.add_argument(
         "-f",
         "--outfile",
         action="store",
         dest="outfile",
-        help="name of the output MP4 file; if not set the animation is "
-        "displayed interactively instead",
+        help="name of the output file (.mp4 or .gif); if not set the "
+        "animation is displayed interactively instead",
     )
     parser.add_argument(
         "--fps",
@@ -237,7 +239,14 @@ def update(frame):
     )
 
     if outfile:
-        writer = animation.FFMpegWriter(fps=fps, bitrate=bitrate)
+        writer: animation.AbstractMovieWriter
+        if outfile.lower().endswith(".gif"):
+            # GitHub's Markdown renderer strips <video> tags for repo-hosted
+            # files, so a GIF (embeddable as a normal image) is required to
+            # show the animation inline in a README.
+            writer = animation.PillowWriter(fps=fps)
+        else:
+            writer = animation.FFMpegWriter(fps=fps, bitrate=bitrate)
         ani.save(outfile, writer=writer)
     else:
         plt.show()

plots.sh

@@ -46,6 +46,6 @@ echo "creating plot closing in to 1.5°C ..."
 echo "creating animated plot ..."
 ./hadcrut5_animate.py \
     --period "1880-1920" \
-    --outfile plots/HadCRUT5-1880-1920-animation.mp4
+    --outfile plots/HadCRUT5-1880-1920-animation.gif
 
 echo "done."