Improve compatibility for h264 ffmpeg-encoded videos.

Default pixel format of yuv444 is, apparently, not widely supported.
Changing to yuv420p fixes playback with Quicktime, on iOS, and with a
wide array of browsers (for HTML5 video).

lib/matplotlib/animation.py

@@ -405,6 +405,12 @@ def output_args(self):
         # The %dk adds 'k' as a suffix so that ffmpeg treats our bitrate as in
         # kbps
         args = ['-vcodec', self.codec]
+        # For h264, the default format is yuv444, which is not compatible with
+        # quicktime (and others). Specifying yuv420p fixes playback on iOS,
+        # as well as HTML5 video in firefox and safari (on both Win and OSX).
+        # Also fixes internet explorer. This is as of 2015/10/29.
+        if self.codec == 'h264':
+            args.extend(['-pix_fmt', 'yuv420p'])
         if self.bitrate > 0:
             args.extend(['-b', '%dk' % self.bitrate])
         if self.extra_args: