GStreamer is a pipeline-based multimedia framework that links together a wide variety of media processing systems to complete complex workflows. For instance, GStreamer can be used to build a system that reads files in one format, processes them, and exports them in another.
GStreamer pipelines adhere to the GStreamer Pipeline Description and consist of an ordered sequence of elements, their configuration properties, and connections are all specified as a list of strings separated by exclamation marks (!). Internally the GStreamer library constructs a pipeline object that contains the individual elements and handles common operations such as clocking, messaging, and state changes.
Example: gst-launch-1.0 videotestsrc ! ximagesink
An element is the fundamental building block of a pipeline.
Elements perform specific operations on incoming frames and then push the resulting frames
downstream for further processing. Elements are linked together textually by exclamation marks (!) with the full chain of elements
representing the entire pipeline. Each element will take data from its upstream element, process it and then output the data for further processing by the next element.
Elements designated as source elements provide input into the pipeline from external sources. Elements designated as sink elements represent the final stage of a pipeline. As an example a sink element could write transcoded frames to a file on the local disk or open a window to render the video content to the screen or even re-stream the content via RTSP.
Object detection pipelines typically use the decodebin utility element to construct a set of decode operations based on the given input format, decoder and demuxer elements available in the system. The next step in the pipeline is often color space conversion which is handled by the videoconvert element.
Elements are configured using key-value pairs called properties. As an example the filesrc element has a property named location which specifies the file path for input.
Example:
filesrc location=cars_1900.mp4
A list of properties supported by each element can be viewed using the command line tool gst-inspect-1.0. The tool also provides a property description and
the valid range of values that can be set.