ffmpeg -f gif -i imagen.gif video.mp4

ffmpeg -i animated.gif -movflags faststart -pix_fmt yuv420p -vf "scale=trunc(iw/2)*2:trunc(ih/2)*2" video.mp4

convert from gif to webm:
ffmpeg -f gif -i cat.gif cat.webm
If you don't have ffmpeg, try avconv.

Convert Gif to MP4:
ffmpeg -f gif -i cat.gif cat.mp4

Convert mov to MP4:
ffmpeg -f mov -i cat.mov cat.mp4

Converter qualquer formato de video em MP4
ffmpeg -i video.xxx novo.mp4