Mediastreamer2 - the multimedia streaming engine

Features

• Read/Write from to an alsa device, an oss device, a windows waveapi device
• Send and receive RTP packets
• Encode and decode the following formats: speex, G711, GSM, H263, theora, iLBC, MPEG4, and H264.
• Read and write from/to a wav file
• Read YUV pictures from a webcam (provided that it has video4linux v1 or v2 driver)
• Display YUV pictures (using SDL library or native apis on windows)
• Dual tones generation
• Echo cancelation, using the extraordinary echo canceler algorithm from the speex library
• Audio conferencing
• Audio parametric equalizer using a FIR filter
• Volume control, automatic gain control
• Works on linux, windows XP
• macos X audio only, video support in progress

Mediastreamer2 can be extended with dynamic plugins, currently a H264 and an ILBC codec plugins are available.

Design and principles

Each processing entity is contained within a MSFilter object. MSFilter(s) have inputs and/or outputs that can be used to connect from and to other MSFilters.

A trivial example to understand:

• MSRtpRecv is a MSFilter that receives RTP packets from the network, unpacketize them and post them on its only output.
• MSSpeexDec is a MSFilter that takes everything on its input assuming these are speex encoded packets, and decodes them and put the result on its output.
• MSFileRec is a MSFilter that takes everything on its input and write it to wav file (assuming the input is 16bit linear pcm).

MSFilters can be connected together to become filter chain. If we assemble the three above examples, we obtain a processing chain that receives RTP packet, decode them and write the uncompressed result into a wav file.

The execution of the media processing work is scheduled by a MSTicker object, a thread that wakes up every 10 ms to process data in all the MSFilter chains it manages. Several MSTicker can be used simultaneously, for example one for audio filters, one for video filters, or one on each processor of the machine where it runs.

Mediastreamer2 is easy to use

If your intent is simply to create audio and video streams, a simple API is defined in audiostream.h and videostream.h to create audio and video stream.

It can be as simple as:

AudioStream *as=audio_stream_start(.../*list of parameters*/);sleep(10);
audio_stream_stop(as);

If your intent is to add new functionalities to mediastreamer2, you'll be glad to know that implementing a mediastreamer2 filter is very straightforward: no complex declarations, inheritance or such like this.

As an example, have a look at this: it is the 'MSVolume' MSFilter, whose goal is to measure and control loudness of an audio stream.

Thanks to this lightweighted framework, developers can concentrate on what matters: the implementation of the algorithm !

Documentation

Mediastreamer2 is documented using doxygen. You can browse the API documention here.

Mediastreamer2 is suitable for embedded systems

• Mediastreamer2 is light. For example on linux/x86 the full-featured shared library takes around 800ko unstripped and compiled with -g (debug). Data messages that carries the media data within mediastreamer2 chains are optimized using the famous sys-V mblk_t structure. This is to avoid copies as long it is possible and allow low cost fragmentation/re-assemble operations that are very common especially when processing video streams.
• Mediastreamer2 is written in C
• Mediastreamer2 compiles on arm with gcc.
• Mediastreamer2 has only oRTP and libc as minimal dependencies. Others (ffmpeg, speex, alsa...) can be added optionnaly if you need all features.
• Thanks to its plugin architecture, mediastreamer2 can be extended to interface with hardware codecs, for example video codecs dsp.

Download

Mediastreamer2 is part of linphone releases.

You can also use git to retrieve the lastest source code (recommended for developers):

git clone git://git.linphone.org/mediastreamer2.git

License

Mediastreamer2 is licensed under GPL.

Proprietary licenses can be ordered from Belledonne Communications.

Need commercial support for mediastreamer2 ?

Please contact
Belledonne Communications.