Live Asynchronous Audio Video Library

ABOUT

A header-only C++ library which wraps FFmpeg, V4L2, ALSA and Libevent for capturing audio and video from multiple live sources (cameras and microphones) and

• Encoding (video: H264, audio: AAC, MP2 and OPUS)
• Decoding (video: MJPEG) / transcoding (video: MJPEG -> H264)
• Recording to file (MPEGTS and MATROSKA containers, audio and/or video)
• Streaming (HTTP and UDP protocols for MPEGTS and MATROSKA containers)
• Basic image processing

The project is useful for building video surveillance systems as well, consisting in media servers which stream and record at the same time and which can be controlled through MQTT or HTTP commands (see THIS and THIS examples).

It also provides an UDP audio (OPUS) + video (H264) streaming system template with the lowest possible latency.

The project runs on Linux (ALSA and V4L2 devices), but a Windows port is planned (any contribution is welcome!).

FEATURES

• All the audio/video tasks are made with strictly asynchronous multiple pipes, inside one main loop. This allows to create simple, short (a complete live H264 grabber/streamer can be made with less than 40 lines of code, see THIS example), easy to read and intuitive code in which all the pipes can be realized through overloaded operators, in the following form:

while (!LAAVStop)
{
    // Pipe
    grabber >> converter >> encoder >> streamer;
    
    // Audio-video events catcher
    eventsCatcher->catchNextEvent();
}

• Threads are not used at all and they are intentionally discouraged in order to avoid that they can be improperly used for decoupling tasks, without taking advantage from multi-core systems.
• All the audio/video modules (-> classes) make extensive use of templates and all their possible concatenations are checked at compile-time, so to avoid inconsistent pipes.
• All the pipes are safe at runtime. I.E: when a source is disconnected or temporarily unavailable, the main loop can continue without necessarily having to check errors (they can be checked, anyway, by polling the status of each node: see THIS example)
• The library is all RAII-designed (basically it safely wraps Libavcodec/format, V4L and ALSA) and the user doesn't have to bother with pointers and memory management.
• The public API is intended to be intuitive, with a few self-explanatory functions.

COMPILING / RUNNING

Dependencies: FFmpeg >= 4.1 (tested with 4.1 version), Libevent and pkg-config (optional: see the compile command below). FFmpeg needs x264 for H264 support and libopus for OPUS support.

• Include the library global header (LAAV.hpp), as shown in the examples, in YourProgram.cpp and execute:

g++ -Wall -std=c++11 -DLINUX -o YourProgram YourProgram.cpp `pkg-config --libs libavformat libavcodec libavutil libswresample libswscale libevent alsa`

• Execute ./CompileExamples for compiling the provided examples.
• API documentation in HTML format can be created by executing, inside the doxy directory:

doxygen Doxyfile

The library has been tested with the VLC, FFPLAY and MPV media players, but other players should work as well. In order to reduce the network streams' latency, use the following flags on the client side:

VLC (tested with v2.2.4: set a low value for --network-caching flag):

vlc --network-caching 200 http://stream_url

FFPLAY:

ffplay -fflags nobuffer http://stream_url

HOW TO USE IT

See the provided EXAMPLES

TODO

• Improve the compile-time error messages, for inconsistent pipes, with more static_assert(...) calls.
• Add a RTSP/RTP streaming server.
• Windows port (basically, it will consist in creating Windows based classes corresponding to the ALSAGrabber and V4L2Grabber classes, with the same API, and few other things: any contribution is welcome!).
• MPEGTS-MJPEG is currently NOT supported.