ffmpeg convert gif to mp4, for best cross browser compatibility

gistfile1.txt

### Full command line options

```
ffmpeg -f gif -i FOO.gif -pix_fmt yuv420p -c:v libx264 -movflags +faststart -filter:v crop='floor(in_w/2)*2:floor(in_h/2)*2' BAR.mp4
```

### Notie

 * output mp4 is encoded with h264, support Firefox/Chrome/Safari in Windows, Mac OSX, Android, and iOS.
 * one mp4 file for all platforms, there is no need to encode an extra `webm` movie, which encoding speed is pretty slow.
 * format as `yuv420p` for Firefox compatibility, the downside is color becomes less-saturate than original gif.
 * yuv420p only support even width/height, so crop filter is required
 * `-movflags +faststart` flags are optimized for online view in browser
 * compression ratio typically 10:1, pretty awesome. note that if original gif is < 512KB, convert as mp4 is less efficient.

### Obtain static binary ffmpeg

 * http://johnvansickle.com/ffmpeg/