View source for Documentation:Modules/rtp

{{See also|Documentation:Modules/live555}}
{{Module|name=rtp|type=Access|first_version=0.7.0|description=Real-Time Protocol ([[RTP]]) input|sc=dccp|sc2=rtptcp|sc3=udplite}}

The only supported format for <code>rtp-dynamic-pt</code> is <code>[[theora]]</code>.

== SRTP ==
The module supports RTP with encryption ([[SRTP]]) through {{VLCSourceFile|modules/access/rtp/srtp.c|l=srtp.c}} using [https://directory.fsf.org/wiki/Libgcrypt libgcrypt] ([https://www.gnupg.org/documentation/manuals/gcrypt/ gcrypt manual]). There are no sub-modules or other shortcuts (in particular, <kbd>srtp</kbd> will not work).

Hexadecimal strings are base-16 numbers. Each character is one of <kbd>0123456789abcdef</kbd> (case-insensitive).

=== Crypto ===
Functions of interest (defined in {{VLCSourceFile|modules/access/rtp/srtp.c|l=srtp.c}} and {{VLCSourceFile|modules/access/rtp/srtp.h|l=srtp.h}}) lie in {{VLCSourceFile|modules/access/rtp/rtp.c|l=rtp.c}} between:
<syntaxhighlight lang="c">
#ifdef HAVE_SRTP
</syntaxhighlight>
and
<syntaxhighlight lang="c">
#endif
</syntaxhighlight>

In summary:
* SRTP sessions are one-way and re-keyed periodically
* To set or reset the master key and master salt for an SRTP session <code>int srtp_setkey (srtp_session_t *s, const void *key, size_t keylen, const void *salt, size_t saltlen)</code> is called
* The <code>setkey</code> values are currently hard-coded as [[wikipedia:Advanced Encryption Standard|AES]] in [[wikipedia:Block cipher mode of operation#CTR|counter mode]] authenticated with [[wikipedia:HMAC|HMAC]]-[[wikipedia:SHA1|SHA1]]; the salt with [[wikipedia:Pseudorandom function family|PRF]]-AES-CM. There are code comments suggesting this be improved
** [https://shattered.io/ SHA1 is deprecated] but using it here should be passably secure for now
* There are explanations (for hackers) in the form of code comments in the files

== Options ==
{{Option
|name=rtcp-port
|value=integer
|min=0
|max=65535
|description=[[RTCP]] packets will be received on this transport protocol [[port]]. If zero, [[multiplex]]ed RTP/RTCP is used
|default=0
}}
{{Option
|name=srtp-key
|value=string
|description=[[RTP]] packets will be authenticated and deciphered with this Secure RTP master shared secret key. This must be a 32-character-long hexadecimal string
}}
{{Option
|name=srtp-salt
|value=string
|description=[[SRTP|Secure RTP]] requires a (non-secret) master [[wikipedia:salt (cryptography)|salt]] value. This must be a 28-character-long hexadecimal string
}}
{{Option
|name=rtp-max-src
|value=integer
|min=1
|max=255
|description=How many distinct active RTP sources are allowed at a time
|default=1
}}
{{Option
|name=rtp-timeout
|value=integer
|description=How long to wait (in seconds) for any packet before a source is expired
|default=5
}}
{{Option
|name=rtp-max-dropout
|value=integer
|min=0
|max=32767
|description=RTP packets will be discarded if they are too much ahead (i.e. in the future) by this many packets from the last received packet
|default=3000
}}
{{Option
|name=rtp-max-misorder
|value=integer
|min=0
|max=32767
|description=RTP packets will be discarded if they are too far behind (i.e. in the past) by this many packets from the last received packet
|default=100
}}
{{Option
|name=rtp-dynamic-pt
|value=string
|description=This payload format will be assumed for dynamic payload types (between 96 and 127) if it can't be determined otherwise with out-of-band mappings ([[SDP]])
|default=NULL
}}

== Source code ==
* {{VLCSourceFile|modules/access/rtp/rtp.c}}

{{Documentation}}