GStreamer Elements

["Milosz Derezynski" <internalerror gmail com>]

Hi All,

With GStreamermm progressing, we need to look at how to access individual elements in a C++-ish fashion.
I'll make a small introduction into the topic here:

GStreamer is based on a plugin based architecture, this means that it in itself is only a framework, and individual plugins exist which range from source elements (which provide data to be decoded) to decoders, demuxers, processors, and output plugins. GST terminology calls these "elements".

Elements can have a lot of signals and properties, which are simply GLib signals and GLib object properties and are important for coding with GStreamer (they can not just be ignored for gstmm).

How i thought of accessing them is using a code generator: It would scan the relevant element and generate a shallow wrapper class e.g. GstElementFilesrc ( : public GstElement ) with the relevant properties and signals present; this could then be added to the project's code and used to access this element.

Firstly it might seem problematic to do this, namely, to create code with a generator on the developer's computer, and then distribute this code with the entire source package, but, in practice, there seems to be no problem:

- GStreamer never creates backwards incompatibility in elements with progressing version numbers; if anything then a new element is created instead which is incompatible (e.g. decodebin2 for incompatible decodebin changes)

- If an element will not wrap correctly into the generated code then it would be also incompatible using the C interface, just that the C interface is much more lax (g_signal_connect failing with g_warnings, g_object_set/get as well), but either way the program wouldn't be guaranteed anymore to run correctly, hence using a precreated wrapper class for C++ doesn't really make a difference in this regard; if anything then we have stricter checking whether the user's installed system will be compatible with the program

The code for this generator could be based on gst-inspect, which prints the properties, signals and other information about elements through inspection.

Comments are welcome :)

-- Milosz