I think that's the software AAC decoder, so source code should be
present in AOSP under frameworks/base/media/libstagefright. Add some
logs in software AAC to see where it is passing that error code up to
OMXCodec.
Another idea is to use a host-based media analyzer tool to examine the
headers for the audio portion of the content -- maybe it's an
unsupported AAC variant, a corrupt AAC frame, etc.