gr_read_file_metadata - Man Page

Read in a GNU Radio file with meta data, extracts the header and prints it.

Metadata file source and sink blocks (Tom Rondeau)

Two new blocks implement enhanced file source and sink blocks that incorporate metadata passed using the stream tags feature in GNU Radio. It is now possible to store things like frequency and sample rate into capture files, or whatever key/value pairs you tag onto data streams inside a flowgraph.

http://www.trondeau.com/home/2012/12/15/metadata-file-format.html