[gst-devel] plugin directory/hierarchy

[Thomas Nyberg]

On Wed, Mar 07, 2001 at 10:14:16PM +0100, Wim Taymans wrote:
> In GStreamer all plugins are techically filters, the only way they
> can be considered sources or sinks (input/output) elements is
> by the absence of src/sink pads. 

This really sucks!
If you are writing an application, you should not assume that a given
plugin exists on the system. Perhaps you want to use an alas_sink if it
exists - else an oss_sink. Perhaps someonee has renamed the oss_sink into
audio_output-sink. This is a real problem I believe.

The best way to solve this, and one of the easier, is to create a numeric
identifier for each type. This way you could easily determine what kind
of a filter a filter really is. You do not need to analyze the plugins
kinds of pads to find out if you can use for output.
A simple gst_element_factory_get_type(...) function should do it. Then
you could test the type.

By looking at gst/elements/gstaudiosink.c one finds
...
"Sink/Audio"
...
however, this string is only a description nothing more.

Instead of using Sink/Audio, one could use a enum(whatever...) like
enum {
     SINK = (1 << 0),
     SRC = (1 << 1),
     AUDIO = (1 << 2),
     VIDEO = (1 << 3),
     PARSER = (1 << 4),
     ...
};

By OR-ing these values together the type of the element is easy to test,
and since we use numeric values - not much space is wasted and
spelling-errors are much easier to detect.

It would be easy to determine if a given element was a soundcard by
if ((gst_element_factory_get_type() & (SINK | AUDIO)) == (SINK | AUDIO))
   ...


If we use an int, we have like 32 different kinds of filters, which should
be enough for everyone(pun intended :)

If this isn't enough, one can move onto 64bit and so on... The best approach
is to create a
typedef element_type_t guint32;

It is easy to change this into guint64 and then it only takes a recompile of
all sources for it to work as aspected.


Since an application can test each element-factory present on the system one
can cope with name-changes, "3rd-party"-plugins and so on... 

/Thomas <thomas at codefactory.se>

-- 
Thomas Nyberg                    thomas.nyberg at codefactory.se
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