# Developing applications with GStreamer

How do I compile programs that use GStreamer ?

GStreamer uses pkg-config to assist applications with compilationa and linking flags. pkg-config is already used by GTK+, GNOME, SDL, and others; so if you are familiar with using it for any of those, you're set.

If you're not familiar with pkg-config to compile and link a small one-file program, pass the --cflags and --libs arguments to pkg-config. For example:

    $ gcc `pkg-config --cflags --libs gstreamer-0.6` -o myprog myprog.c

would be sufficient for a gstreamer-only program. If (for example) your app also used GTK+ 2.0, you could use

    $ gcc `pkg-config --cflags --libs gstreamer-0.6 gtk+-2.0` -o myprog myprog.c

Those are back-ticks (on the same key with the tilde on US keyboards), not single quotes.

For bigger projects, you should integrate pkg-config use in your Makefile, or integrate with autoconf using the pkg.m4 macro.

How can I use GConf to get the system-wide defaults ?

It's a good idea to use GConf to use default ways of outputting audio and video. Since GStreamer's GConf keys can be more than just one element, but a whole pipeline, it would be a good idea to use the gstgconf library. It provides functions to parse the GConf key to a usable pipeline.

To link against gstgconf, use pkg-config to query the gstreamer-libs-0.6.pc file for link flags, and add -lgstgconf to the link flags. This fragment of configure.ac shows how to use pkg-config to get the LIBS:

    dnl check for GStreamer helper libs
    PKG_CHECK_MODULES(GST_HELPLIBS, gstreamer-libs-0.6 >= $GSTREAMER_REQ,,exit)
    AC_SUBST(GST_HELPLIBS_LIBS)
    AC_SUBST(GST_HELPLIBS_CFLAGS)

This fragment of a Makefile.am file shows how to make your application link to it:

    bin_PROGRAMS = application

    application_LDADD = $(GST_LIBS) $(GST_HELPLIBS_LIBS) -lgstgconf
    application_CFLAGS = $(GST_CFLAGS) $(GST_HELPLIBS_CFLAGS)

How do I debug these funny shell scripts that libtool makes ?

When you link a program against uninstalled GStreamer using libtool, funny shell scripts are made to modify your shared object search path and then run your program. For instance, to debug gst-launch, try

    libtool gdb /path/to/gstreamer-launch

. If this does not work, you're probably using a broken version of libtool.

Why is mail traffic so low on gstreamer-devel ?

Our main arena for coordination and discussion is IRC, not email. Join us in #gstreamer on irc.freenode.net For larger picture questions or getting more input from more persons, a mail to gstreamer-devel is never a bad idea. However, we do archive our IRC discussions, which you may find in the gstreamer-daily mailing list archives.

What kind of versioning scheme does GStreamer use ?

For public releases, GStreamer uses a standard MAJOR.MINOR.MICRO version scheme. If the release consists of mostly bug fixes or incremental changes, the MICRO version is incremented. If the release contains big changes, the MINOR version is incremented. If we're particularly giddy, we might even increase the MAJOR number. Don't hold your breath for that though.

During the development cycle, GStreamer also uses a fourth or NANO number. If this number is 1, then it's a CVS version. Any tarball or package that has a nano number of 1 is made from CVS and thus not supported. Additionally, if you didn't get this package or tarball from the GStreamer team, don't have high hopes on it doing whatever you want it to do.

If the number is 2 or higher, it's an official pre-release in preparation of an actual complete release. Your help in testing these tarballs and packages is very much appreciated.

What is the coding style for GStreamer core ?

The core is basically coded in K&R with 2-space indenting. Just follow what's already there and you'll be fine. The core could use a code cleanup though at this point.

Individual plugins in gst-plugins or plugins that you want considered for addition to the gst-plugins module should be coded in the same style. It's easier if everything is consistent. Consistency is, of course, the goal.

If you use emacs, try these lines:

    (defun gstreamer-c-mode ()
      "C mode with adjusted defaults for use with GStreamer."
      (interactive)
      (c-mode)
      (c-set-style "K&R")
      (setq c-basic-offset 2))

    (setq auto-mode-alist (cons '("gst.*/.*\\.[ch]$" . gstreamer-c-mode)
                           auto-mode-alist))

Or, run your code through

    indent -br -bad -cbi0 -cli2 -bls -l100 -ut -ce

before submitting a patch (FIXME: check if these are indeed the proper options).

As for the code itself, the GNOME coding guidelines is a good read. Where possible, we try to adhere to the spirit of GObject and use similar coding idioms.