The simplest converter to HTML5 Video (Ogg Theora, MP4, WebM) file groups?

Question

Video

There are several thousand very short videos in AVI format. All these files need to be converted into the three formats listed above, keeping the file name (eg 0001.avi → 0001.mp4). I went through a bunch of converters, but none came up, including due to the lack of support for group conversion.
I really hope for help in finding a subject.

Answer 1

#!/bin/bash
for i in `seq 1 1000`; do
  for f in ogg mp4 webm; do
    ffmpeg -i $(printf "%04d" $i.avi) -f $f $(printf "%04d" $i.$f)
  done
done

Answer 2

Miro Video Converter

Answer 3

For ogg it is also convenient to use ffmpeg2theora