Here is a list of all documented files with brief descriptions:

[detail level 123]

include
ortp
logging.h	Logging API
ortp.h	General purpose library functions
payloadtype.h	Definition of payload types
rtpprofile.h	Using and creating standart and custom RTP profiles
rtpsession.h	The RtpSession api
sessionset.h	Sending and receiving multiple streams together with only one thread
telephonyevents.h	Receiving and sending telephone events (RFC2833)