XMediaLib

XMediaLib is a media and signaling toolkit for VoIP and WebRTC on Erlang/Elixir. It provides wire-format helpers and optional native codecs for RTP/RTCP, SRTP, STUN/TURN, SDP, SIP, and ZRTP. Parts of the API descend from Peter Lemenkov's RTPLib.

Published home: https://github.com/Lazarus404/xmedialib

What problem this solves

Building a phone or conference app means more than HTTP. Peers must agree on codecs and network paths (SDP, ICE), authenticate and encrypt media (DTLS-SRTP in WebRTC, or ZRTP as an in-band alternative), and move packets through NAT (STUN/TURN). XMediaLib packages those building blocks as Elixir modules plus optional NIF- or port-backed drivers where performance matters.

Main modules

• XMediaLib.Codec -- audio encode/decode via native port drivers (G.711, G.722, Opus, and others). Opus in-band FEC/PLC via set_inband_fec/2, decode_fec/2, decode_plc/1; fmtp parse in XMediaLib.Codec.OpusFmtp.
• XMediaLib.Rtp / XMediaLib.Rtcp -- RFC 3550 RTP and RTCP framing; header extensions and Dependency Descriptor helpers under XMediaLib.Rtp.*.
• XMediaLib.Srtp -- SRTP protect/unprotect after key agreement.
• XMediaLib.Stun -- STUN/TURN message encode and decode.
• XMediaLib.SDP -- session description parse and encode.
• XMediaLib.SIP -- SIP message helpers (pure Elixir; optional PJSIP NIF).
• XMediaLib.Zrtp / XMediaLib.ZrtpFsm / XMediaLib.ZrtpCrypto -- ZRTP packet codec, key derivation, and handshake state machine.
• XMediaLib.SAS -- Short Authentication String rendering for ZRTP.
• XMediaLib.CRC32C -- Castagnoli CRC-32C (ZRTP packet trailer).
• XMediaLib.TestUtils -- lab helpers for codec golden-file checks (not for production wire paths).

RFCs

Codecs and media:

• RFC 3551 (RTP profile, static payload types including PCMU/PCMA)
• RFC 3550 (RTP and RTCP)
• RFC 3711 (SRTP)
• ITU-T G.711 (PCMU/PCMA), ITU-T G.722, ITU-T G.729
• RFC 6716 (Opus)
• RFC 4867 (Speex over RTP), RFC 3951 (iLBC)
• RFC 8285 (RTP header extensions); AV1 RTP Dependency Descriptor

Signaling and connectivity:

• RFC 8866 / RFC 4566 (SDP)
• RFC 3261 (SIP)
• RFC 8489 (STUN), RFC 8656 (TURN)

ZRTP and related:

• RFC 6189 (ZRTP)
• RFC 3526 / RFC 5114 (DH groups referenced by ZRTP)
• RFC 8265 (SAS rendering / Base32)
• CRC-32C (Castagnoli); see RFC 3385 / RFC 4960 / RFC 3720 B.4

Prerequisites

To run all tests and use all codec features, install the native libraries the port drivers link against:

• libilbc
• bcg729
• SampleRate
• SpanDSP
• libOpus
• libSpeex

Example on Ubuntu:

# install libilbc
wget https://github.com/TimothyGu/libilbc/releases/download/v2.0.2/libilbc-2.0.2.tar.gz
tar -xzvf libilbc-2.0.2.tar.gz
cd libilbc-2.0.2
./configure
make && sudo make install

# install bcg729
git clone git@github.com:BelledonneCommunications/bcg729.git
cd bcg729/
cmake . -DENABLE_STATIC=YES
make && sudo make install

# install remaining libs
sudo add-apt-repository ppa:jonathonf/ffmpeg-3
sudo apt-get update
sudo apt-get install libsamplerate-dev libspandsp-dev libopus-dev libopus0 opus-tools libspeex-dev

Without these libraries, codec drivers that need them will not load; other modules (RTP, SDP, STUN, and so on) still work.

SIP (optional NIF)

XMediaLib.SIP.parse/1 and encode/1 always work: they use the PJSIP NIF when priv/sip_nif.so is built, otherwise the pure-Elixir fallback (XMediaLib.SIP.Elixir).

Building the NIF requires PJSIP (libpjproject). If PJSIP is not installed, make prints skip sip_nif: PJSIP not found and continues. NIF-specific tests skip automatically; Elixir-path tests always run.

Install PJSIP (example on macOS with Homebrew):

brew install pjproject

Then from xmedialib/:

make
mix test test/sip/

SDP

XMediaLib.SDP.parse/1 and encode/1 parse and serialize Session Description Protocol for WebRTC-oriented offers and answers. Media attributes such as ICE candidates, fingerprints, rtpmap/fmtp, and SCTP data-channel fields are promoted onto %XMediaLib.SDP.Media{}.

mix test test/sdp/

Codec (Opus FEC / PLC)

XMediaLib.Codec loads Erlang port drivers under priv/. Opus supports:

• set_bitrate/2 -- OPUS_SET_BITRATE
• set_inband_fec/2 -- OPUS_SET_INBAND_FEC
• set_packet_loss_perc/2 -- OPUS_SET_PACKET_LOSS_PERC (0..100)
• decode/2 -- normal decode (fec=0)
• decode_fec/2 -- recover the previous lost frame from in-band FEC in this packet (fec=1)
• decode_plc/1 -- concealment from decoder state (NULL packet)

Non-Opus codecs return {:error, :unsupported} for FEC/PLC setters and decoders (no silent no-op). Parse SDP fmtp with XMediaLib.Codec.OpusFmtp.parse/1, then call set_inband_fec/2 after start_link/1 when useinbandfec is true.

mix test test/codecs/codec_opus_test.exs

Installation

Add xmedialib to your mix.exs dependencies:

def deps do
  [{:xmedialib, "~> 0.3.0"}]
end

Contact

For questions or suggestions, email experts@xirsys.com

Copyright

Copyright (c) 2013 - 2026 Jahred Love & Xirsys LLC

All rights reserved.

XMediaLib is licensed by Xirsys, with permission, under the Apache License Version 2.0. See LICENSE for the full license text.