gstreamer/markdown/frequently-asked-questions/developing.md

Developing applications with GStreamer

How do I compile programs that use GStreamer ?

This depends all a bit on what your development environment and target operating systems is. The following is mostly aimed at Linux/unix setups.

GStreamer uses the pkg-config utility to provide applications with the right compiler and linker flags. pkg-config is a standard build tool that is widely used unix systems to locate libraries and retrieve build settings, so if you're familiar with using it already then you're basically 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:

$ libtool --mode=link gcc `pkg-config --cflags --libs gstreamer-1.0` -o myprog myprog.c

would be sufficient for a gstreamer-only program. If (for example) your application also used GTK+ 3.0, you could use

$ libtool --mode=link gcc `pkg-config --cflags --libs gstreamer-1.0 gtk+-3.0` -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 (providing PKG_CONFIG_CHECK).

How do I develop against an uninstalled GStreamer copy ?

It is possible to develop and compile against an uninstalled copy of gstreamer and gst-plugins-* (for example, against git checkouts). This allows you to develop against and test the latest GStreamer version without having to install it and without interfering with your system-wide GStreamer setup.

There are two ways to achieve such a setup:

1. gst-build is our new meta-build module based on the Meson build system. This is the shiny new thing. It's fast and simple to get started with, but you will need a recent version of Meson installed. Just check out the git repository and run the setup.py script. Once the initial meson configure stage has passed, you can enter an uninstalled environment by running ninja uninstalled in the build directory. This will make sure tools and plugin from the uninstalled build tree will be used. Any problems, let us know.

2. gst-uninstalled is our traditional autotools- and libtool-based build setup. The easiest way too create such a setup is using the latest version of the create-uninstalled-setup.sh script. This setup makes use of the latest version of the gst-uninstalled script. Running this script, you'll be in an environment where the uninstalled tools and plugins will be used by default. Also, pkg-config will detect the uninstalled copies before (and prefer them to) any installed copies.

Multiple uninstalled setups can be used in parallel, e.g. one for the latest stable branch and one for git master. Have a look at the gst-uninstalled script to see how it determines which environment is used.

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

For GNOME applications it's a good idea to use GConf to find the default ways of outputting audio and video. You can do this by using the 'gconfaudiosink' and 'gconfvideosink' elements for audio and video output. They will take care of everything GConf-related for you and automatically use the outputs that the user configured. If you are using gconfaudiosink, your application should set the 'profile' property.

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 --mode=execute gdb /path/to/gst-launch

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

If you build GStreamer using the Meson build system, libtool will not be used and this is not a problem. You can run gdb, valgrind or any debugging tools directly on the binaries Meson creates in the build directory.

Why is mail traffic so low on gstreamer-devel ?

Our main arena for coordination and discussion are IRC and bugzilla, not mailing lists. Join us in #gstreamer on irc.freenode.net. There is also a webchat interface. For larger picture questions or getting more input from more people, a mail to the gstreamer-devel mailing list is never a bad idea, however.

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. A change in the MAJOR version indicates incompatible API or ABI changes, which happens very rarely (the last one dates back to 2012). This is also known as semantic versioning.

Even MINOR numbers indicate stable releases: 1.0.x, 1.2.x, 1.4.x, 1.6.x, 1.8.x, and 1.10.x are our stable release series. Odd MINOR numbers are used for unstable development releases and prereleases which should only be used temporarily for testing; your help in testing these tarballs and packages is very much appreciated!

During the development cycle, GStreamer also uses a fourth or NANO number. If this number is 1, then it's a git development version. Any tarball or package that has a nano number of 1 is made from git 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.

What is the coding style for GStreamer code?

The core and almost all plugin modules are basically coded in K&R with 2-space indenting. Just follow what's already there and you'll be fine.

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

Simply run your code (only the *.c files, not the header files) through

indent \
  --braces-on-if-line \
  --case-brace-indentation0 \
  --case-indentation2 \
  --braces-after-struct-decl-line \
  --line-length80 \
  --no-tabs \
  --cuddle-else \
  --dont-line-up-parentheses \
  --continuation-indentation4 \
  --honour-newlines \
  --tab-size8 \
  --indent-level2

before submitting a patch. (This is using GNU indent.) There is also a gst-indent script in the GStreamer core source tree in the tools directory which wraps this and contains the latest option. The easiest way to get the indenting right is probably to develop against a git checkout. The local git commit hook will ensure correct indentation. We only require code files to be indented, header files may be indented manually for better readability (however, please use spaces for indenting, not tabs, even in header files).

Comments should be in /* ANSI C comment style */ and code should generally be compatible with ANSI C89, so please declare all variables at the beginning of the block etc.

Patches should ideally be made against git master or a recent release and should be created using git format-patch format. They should then be attached individually to a bug report or feature request in bugzilla. Please don't send patches to the mailing list, they will likely get lost there.

See How to submit patches for more details.

I have translated one of the module .po files into a new language. How do I get it included?

GStreamer translations are uniformly managed through the Translation Project. There are some instructions on how to join the Translation Project team and submit new translations at http://translationproject.org/html/translators.html.

New translations submitted via the Translation Project are merged periodically into git by the maintainers by running make download-po in the various modules when preparing a new release.

We won't merge new translations or translation fixes directly, everything must go via the Translation Project.