MP4 container writer in Java

Question

I would like to find a FREE MP4 (container) writer for Java. I do not need an encoder, only something which can write the correct atoms given their expected values. Bonus

Answer 1

The Java I've seen which modifies MP4 files would invoke Nero AAC Codec externally (a Windows native .exe which Nero does not supply the source for) to modify AAC files (which are Apple's audio-only MP4 files). It works for audio only, not to video.