The two RTP analysis utilities rtp-gsmfr-dump and rtp-gsmfr-extr support the
following RTP payload formats for FR/EFR codec frames and BFI markers:

* Standard RFC 3551 (same as TS 101 318) format for good frames

* TRAUlike RTP payload format defined here:

https://www.freecalypso.org/hg/themwi-system-sw/file/tip/doc/RTP-TRAUlike-format

* Old BFI marker format defined here:

https://www.freecalypso.org/hg/themwi-system-sw/file/tip/doc/RTP-BFI-extension

* Zero-length RTP payload serving as a BFI marker

All of these formats are distinguished by rtp-gsmfr-dump in its human-oriented
dump output, but not all of them can be represented losslessly in the gsmx
binary file format defined in our Themyscira Wireless GSM codec libraries and
utilities package.  The latter on-disk file format requires plain RFC 3551
format for good frames and the old Themyscira 2-byte BFI marker format for bad
frames; rtp-gsmfr-extr converts everything into this fixed format.