Wouldn’t something like this work for H.264?
jcodec - a pure java implementation of video/audio codecs.
About
JCodec is a library implementing a set of popular video and audio codecs. Currently JCodec supports:
Video codecs
H.264 main profile decoder;
H.264 baseline profile encoder;
VP8 decoder (I frames only);
VP8 encoder (I frames only);
MPEG 1/2 decoder ( I/P/B frames, interlace );
Apple ProRes decoder/encoder;
JPEG decoder;
PNG decoder/encoder.
DivX/Xvid
Audio codecs
SMPTE 302M decoder;
AAC decoder (JAAD)
RAW PCM.
Formats:
MP4 ( MOV ) demuxer / muxer;
MKV ( Matroska ) demuxer / muxer;
MPEG PS demuxer;
MPEG TS demuxer;
WAV demuxer/muxer;
MPEG Audio (MP3) demuxer;
ADTS demuxer.
DPX parser
JCodec is free software distributed under FreeBSD License.