We describe what we try to achieve with GStreamer.
GStreamer wants to provide a clean interface to:
The application programmer who wants to build a media pipeline. The programmer can use an extensive set of powerful tools to create media pipelines without writing a single line of code. Performing complex media manipulations becomes very easy.
The plugin programmer. Plugin programmers are provided a clean and simple API to create self-contained plugins. An extensive debugging and tracing mechanism has been integrated. GStreamer also comes with an extensive set of real-life plugins that serve as examples too.
GStreamer adheres to the GLib 2.0 object model. A programmer familiar with GLib 2.0 or older versions of GTK+ will be comfortable with GStreamer.
GStreamer uses the mechanism of signals and object properties.
All objects can be queried at runtime for their various properties and capabilities.
GStreamer intends to be similar in programming methodology to GTK+. This applies to the object model, ownership of objects, reference counting, ...
All GStreamer Objects can be extended using the GObject inheritance methods.
All plugins are loaded dynamically and can be extended and upgraded independently.
Plugins are shared libraries that are loaded at runtime. Since all the properties of the plugin can be set using the GObject properties, there is no need (and in fact no way) to have any header files installed for the plugins.
Special care has been taken to make plugins completely self-contained. All relevant aspects of plugins can be queried at run-time.
High performance is obtained by:
g_mem_chunk and fast
non-blocking allocation algorithms where possible to
minimize dynamic memory allocation.
extremely light-weight links between plugins. Data can travel the pipeline with minimal overhead. Data passing between plugins only involves a pointer dereference in a typical pipeline.
providing a mechanism to directly work on the target memory. A plugin can for example directly write to the X server's shared memory space. Buffers can also point to arbitrary memory, such as a sound card's internal hardware buffer.
refcounting and copy on write minimize usage of memcpy. Sub-buffers efficiently split buffers into manageable pieces.
the use of cothreads to minimize the threading overhead. Cothreads are a simple and fast user-space method for switching between subtasks. Cothreads were measured to consume as little as 600 cpu cycles.
allowing hardware acceleration by using specialized plugins.
using a plugin registry with the specifications of the plugins so that the plugin loading can be delayed until the plugin is actually used.
all critical data passing is free of locks and mutexes.
The core of GStreamer is essentially media-agnostic. It only knows about bytes and blocks, and only contains basic elements. The core of GStreamer is functional enough to even implement low-level system tools, like cp.
All of the media handling functionality is provided by plugins external to the core. These tell the core how to handle specific types of media.
GStreamer also wants to be an easy framework where codec developers can experiment with different algorithms, speeding up the development of open and free multimedia codecs like Theora and Vorbis.