I would recommend JAVE.
The JAVE (Java Audio Video Encoder) library is Java
wrapper on the ffmpeg project. Developers can take take
advantage of JAVE to transcode audio and video files from a format to
another. This description is taken from here.
JAVE supports (some examples):
- transcode an AVI file to a MPEG
- convert a WAV audio file to a MP3 or a Ogg Vorbis
- separate and transcode audio and video trackseparate and transcode audio and video tracks
- resize videos
I and my friend have used this library to build our project (part of course assignment), ami-converter, a desktop-based multimedia converter. With this library, we can convert original format of audio and video into another format. You might wonder the audio and video codecs that supported by JAVE, audio and video attributes, and anything else. I suggest you to read the documentation.
Something that I don't know about JAVE is splitting a video in many parts, like you said before. At least, JAVE supports video format conversion.
The latest version of JAVE is released on April, 15 2009 (very old). I think it's still good library, though.