Introduction to PJMEDIA

PJMEDIA is a fully featured media stack, distributed under Open Source/GPL terms, and featuring small footprint and good extensibility and excellent portability. Here are some brief overview of PJMEDIA benefits.

Benefits

Many Features

PJMEDIA has many features, and rather than to list them all here, please see the Modules page for more info.

Video is planned to arrive at version 2.

Excellent Portability

It's been ported to all desktop systems and many mobile platforms including Symbian, Windows Mobile, iPhone, and Android. Thanks to its zero thread design, users have been able to run PJMEDIA on deeply embedded platforms, even without operating systems (those typically found in DSP platforms). Except the echo suppressor, all other PJMEDIA components have fixed point implementation, which makes it ideal for embedded systems which lack FPU. PJMEDIA also has tiny footprint, as explained below

Tiny Footprint

Lets not talk about less meaningful and potentially misleading term such as core footprint, and instead here is the footprint of all components typically used to build a full streaming media:

Category        Component       text    data    bss     dec     filename
-------------------------------------------------------------------------------
Core            Error subsystem 135     0       0       135     errno.o
Core            Endpoint        4210    4       4       4218    endpoint.o
Core            Port framework  652     0       0       652     port.o
Core            Codec framework 6257    0       0       6257    codec.o
Codec           Alaw/ulaw conv. 1060    16      0       1076    alaw_ulaw.o
Codec           G.711           3298    128     96      3522    g711.o
Codec           PLC             883     24      0       907     plc_common.o
Codec           PLC             7130    0       0       7130    wsola.o
Session         Stream          12222   0       1920    14142   stream.o
Transport       RTCP            3732    0       0       3732    rtcp.o
Transport       RTP             2568    0       0       2568    rtp.o
Transport       UDP             6612    96      0       6708    transport_udp.o
Transport       Jitter buffer   6473    0       0       6473    jbuf.o
-------------------------------------------------------------------------------
TOTAL                          55,232   268    2,020    57,520

The 56KB are for media streaming components, complete with codec, RTP, and RTCP. The footprint above was done for PJSIP version 1.8.2 on a Linux x86 machine, using footprintopimization as explained in PJSIP FAQ. Numbers are in bytes.

Good Quality

PJMEDIA supports wideband, ultra-wideband, and beyond, as well as multiple audio channels. The jitter buffer has been proven to work on lower bandwidth links such as 3G, and to some extent, Edge and GPRS. We've grown our own algorithm to compensate for packet losses and clock drifts in audio transmission, as well as feature to use codec's built in PLC if available.

Hardware Support

PJMEDIA supports hardware, firmware, or other built-in feature that comes with the device. These are crucial for mobile devices to allow the best use of the very limited CPU and battery power of the device. Among other things, device's on-board codec and echo cancellation may be used if available.

Extensible

Despite its tiny footprint, PJMEDIA uses a flexible port concept, which is adapted from filter based concept found in other media framework. It is not as flexible as those found in Direct Show or gstreamer (and that would be unnecessary since it serves different purpose), but it's flexible enough to allow components to be assembled one after another to achieve certain task, and easy creation of such components by application and interconnect them to the rest of the framework.

(Fairly Okay) Documentation

We understand that any documentation can always be improved, but we put a lot of efforts in creating and maintaining our documentation, because we know it matters.

Organization

At the top-most level, PJMEDIA library suite contains the following libraries.

PJMEDIA

This contains all main media components. Please see the Modules page for complete list of components that PJMEDIA provides.

PJMEDIA Codec

PJMEDIA-CODEC is a static library containing various codec implementations, wrapped into PJMEDIA codec framework. The static library is designed as such so that only codecs that are explicitly initialized are linked with the application, therefore keeping the application size in control.

Please see Codec Framework for more info.

PJMEDIA Audio Device

PJMEDIA-Audiodev is audio device framework and abstraction library. Please see Audio Device API for more info.

PJMEDIA Key Concepts

Below are some key concepts in PJMEDIA: