Change in the default animation codec

To generate a video output of animated plots, a more efficient codec, H.264, is now used by default in place of MPEG-4. As H.264 has a higher compression rate, the smaller output file size permits longer video record time and reduces the time and network data needed to load them. Real-time playback of H.264 videos is generally more fluent and in better quality than those encoded in MPEG-4.