diff --git a/interlace-frames.py b/interlace-frames.py
index 243e565..3e777b4 100644
--- a/interlace-frames.py
+++ b/interlace-frames.py
@@ -12,42 +12,69 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-"""Script to take a set of frames (PNG files) for a recovery animation
-and turn it into a single output image which contains the input frames
-interlaced by row.  Run with the names of all the input frames on the
-command line, in order, followed by the name of the output file."""
+"""
+Script to take a set of frames (PNG files) for a recovery animation and turn
+it into a single output image which contains the input frames interlaced by
+row. Run with the names of all the input frames on the command line. Specify
+the name of the output file with -o (or --output), and optionally specify the
+number of frames per second (FPS) with --fps (default: 20).
 
+e.g.
+interlace-frames.py --fps 20 --output output.png frame0.png frame1.png frame3.png
+"""
+
+from __future__ import print_function
+
+import argparse
 import sys
 try:
   import Image
   import PngImagePlugin
 except ImportError:
-  print "This script requires the Python Imaging Library to be installed."
+  print("This script requires the Python Imaging Library to be installed.")
   sys.exit(1)
 
-frames = [Image.open(fn).convert("RGB") for fn in sys.argv[1:-1]]
-assert len(frames) > 0, "Must have at least one input frame."
-sizes = set()
-for fr in frames:
-  sizes.add(fr.size)
 
-assert len(sizes) == 1, "All input images must have the same size."
-w, h = sizes.pop()
-N = len(frames)
+def interlace(output, fps, inputs):
+  frames = [Image.open(fn).convert("RGB") for fn in inputs]
+  assert len(frames) > 0, "Must have at least one input frame."
+  sizes = set()
+  for fr in frames:
+    sizes.add(fr.size)
 
-out = Image.new("RGB", (w, h*N))
-for j in range(h):
-  for i in range(w):
-    for fn, f in enumerate(frames):
-      out.putpixel((i, j*N+fn), f.getpixel((i, j)))
+  assert len(sizes) == 1, "All input images must have the same size."
+  w, h = sizes.pop()
+  N = len(frames)
 
-# When loading this image, the graphics library expects to find a text
-# chunk that specifies how many frames this animation represents.  If
-# you post-process the output of this script with some kind of
-# optimizer tool (eg pngcrush or zopflipng) make sure that your
-# optimizer preserves this text chunk.
+  out = Image.new("RGB", (w, h*N))
+  for j in range(h):
+    for i in range(w):
+      for fn, f in enumerate(frames):
+        out.putpixel((i, j*N+fn), f.getpixel((i, j)))
 
-meta = PngImagePlugin.PngInfo()
-meta.add_text("Frames", str(N))
+  # When loading this image, the graphics library expects to find a text
+  # chunk that specifies how many frames this animation represents.  If
+  # you post-process the output of this script with some kind of
+  # optimizer tool (eg pngcrush or zopflipng) make sure that your
+  # optimizer preserves this text chunk.
 
-out.save(sys.argv[-1], pnginfo=meta)
+  meta = PngImagePlugin.PngInfo()
+  meta.add_text("Frames", str(N))
+  meta.add_text("FPS", str(fps))
+
+  out.save(output, pnginfo=meta)
+
+
+def main(argv):
+  parser = argparse.ArgumentParser()
+  parser.add_argument('--fps', default=20)
+  parser.add_argument('--output', '-o', required=True)
+  parser.add_argument('input', nargs='+')
+  args = parser.parse_args(argv)
+
+  interlace(args.output, args.fps, args.input)
+
+
+if __name__ == '__main__':
+  main(sys.argv[1:])
+