Which parameter in RMOpenFileMP4()? (Write sigma codec)

[systest]

Hi, I'm writing a codec module for VLC use sigma library.

And for decode mpeg4 file, RMOpenFileMP4() or RMOpenUrlMP4() must be used,

RM_EXTERN_C RMstatus RMOpenFileMP4(const RMnonAscii *filename,
RMascii *fileType,
ExternalRMmp4Client *mp4c);

RM_EXTERN_C RMstatus RMOpenUrlMP4 ( const RMascii * url,
ExternalRMmp4Client * mp4c
)

And in VLC codec module, how can I get the mpeg4 filename or the URL?
Or, how can I get the stream data in VLC codec module?