nx_metadata_sdk
1.0
Metadata SDK
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// Copyright 2018-present Network Optix, Inc. Licensed under MPL 2.0: www.mozilla.org/MPL/2.0/
The whole contents of this package, including all C/C++ source code, is licensed as Open Source under the terms of Mozilla Public License 2.0: www.mozilla.org/MPL/2.0/, with the possible exception of certain files which may be licensed under the terms of other open-source licenses explicitly referenced in those files.
See the license texts in license_*.md
files in the root directory of this package.
This package provides an SDK to create so-called Analytics Plugins for the Video Management System (VMS).
From the business logic point of view, a typical Analytics Plugin is connected to a video camera, may receive video frames from the camera or interact with the camera using a certain proprietary way, and may generate metadata - events and objects (rectangles on a frame) - which is sent to the Server to be stored in its database and visualized in the Client.
From the developers' point of view, an Analytics Plugin is a dynamic library (.dll
on Windows, .so
on Linux) which exports a single extern "C"
entry point function. Such function is a factory for objects inherited from a dedicated SDK abstract class (in other words, implementing a dedicated interface) class nx::sdk::analytics::IPlugin
(src/nx/sdk/analytics/i_plugin.h
), derived from class nx::sdk::IPlugin
(src/nx/sdk/i_plugin.h
). This base interface also defines the name and the prototype of the entry point function.
To make it possible to develop plugins using a different C++ compiler (e.g. with an incompatible ABI) rather than the one used to compile the VMS itself, or potentially in languages other than C++, a COM-like approach is offered: all objects created in a plugin or passed to a plugin inherit abstract classes declared in header files of this SDK, which have only pure virtual functions with C-style arguments (not using C++ standard library classes). To manage lifetime of such objects, they incorporate a reference counter.
The SDK C++ files have extensive documentation comments in Doxygen format, from which HTML files are generated and included into the SDK: see docs/html/index.html
.
To simplify implementation of a plugin, a number of helper classes are provided with this SDK that implement the SDK interfaces and handle such complexities as reference counting and interface requesting. Such classes are located in folders named helpers
. If such a helper class does not address all the requirements of the plugin author, it may be subclassed or not used at all - the plugin can always implement everything from scratch using just interfaces from the header files.
Also, some tools are provided with this SDK, which are recommended though not required to be used by a plugin:
src/nx/sdk/helpers/
- utilities and typical/base classes implementing interfaces, including:ref_countable.h
- class nx::sdk::RefCountable
: base class for objects implementing IRefCountable
interface.ptr.h
- class nx::sdk::Ptr
: Smart Pointer to reference-countable objects.to_string.h
and src/nx/sdk/helpers/uuid_helper.h
: Conversion functions.src/nx/sdk/analytics/helpers/
- Analytics-related utilities and typical/base classes implementing interfaces, including:plugin.h
- class nx::sdk::analytics::Plugin
: Base class for a typical implementation of the nx::sdk::analytics::IPlugin
interface; use it to start developing an Analytics Plugin.pixel_format.h
: Utilities for enum IUncompressedFrame::PixelFormat
.nx_kit
(which itself is an independent project with its own documentation) that offers convenient debug output (logging) and support for .ini files with options for experimenting (e.g. switching alternative implementations, or parameterizing the code), and a rudimentary framework for simple unit tests (used by the SDK itself, and plugin samples).The recommended way to start developing a plugin is the following: inherit your classes from nx::sdk::analytics::Plugin
, nx::sdk::analytics::Engine
and nx::sdk::analytics::DeviceAgent
according to the Doxygen comments in those classes and interfaces they implement.
This package includes a sample Analytics Plugin written in C++: Stub Analytics Plugin
, located at samples/stub_analytics_plugin/
. It receives video frames from a camera, ignores them, and generates stub metadata Objects looking as a rectangle moving diagonally across the frame, and also some hard-coded Events. This plugin has certain settings which allow to test various SDK features, some of its settings (those related to the Plugin object) are located in stub_analytics_plugin_ini.h
.
The included Stub Analytics Plugin
source files can be compiled and linked using CMake, yielding stub_analytics_plugin.dll
on Windows, or libstub_analytics_plugin.so
on Linux.
Prerequisites:
To compile the sample, and (if not cross-compiling) run unit tests, execute the commands collected into the provided scripts (use their source code as a reference):
On Windows, after CMake generation phase, Visual Studio GUI can be used to compile the sample: open ..\metadata_sdk-build\stub_analytics_plugin.sln
and build the ALL_BUILD
project. Make sure that the platform combo-box is set to "x64".
After successful build, locate the main built artifact:
To install the plugin, just copy its library file to the dedicated folder in the VMS Server installation directory:
ATTENTION: After copying the plugin library, the Server has to be restarted.