================================= GStreamer Static Linking README ================================= DRAFT, April 2013 I. INTRODUCTION It is possible to link GStreamer libraries, plugins and applications statically, both in case of free/libre/open-source software applications and proprietary applications. On some platforms static linking may even be required. However, distributing statically linked binaries using GStreamer usually requires additional effort to stay compliant with the GNU LGPL v2.1 license. The purpose of this document is to draw attention to this fact, and to summarise in layman's terms what we believe is required from anyone distributing statically linked GStreamer binaries. Most of this also applies to dynamically linked GStreamer binaries. II. DISCLAIMER This document is not legal advice, nor is it comprehensive. It may use words in ways that do not match the definition or use in the license text. It may even be outright wrong. Read the license text for all the details, it is the only legally binding document in this respect. This document is primarily concerned with the implications for the distribution of binaries based on LGPL-licensed software as imposed by the LGPL license, but there may be other restrictions to the distribution of such binaries, such as terms and conditions of distribution channels (e.g. "app stores"). III. THE SPIRIT OF THE LGPL LICENSE The GNU LGPL v2.1 license allows use of such-licensed software by proprietary applications, but still aims to ensure that at least the LGPL-licensed software parts remain free under all circumstances. This means any changes to LGPL-licensed source code must be documented and be made available on request to those who received binaries of the software. It also means that it must be possible to make changes to the LGPL-licensed software parts and make the application use those, as far as that is possible. And that recipients of an application using LGPL-licensed software are made aware of their rights according to the LGPL license. In an environment where GStreamer libraries and plugins are used as dynamically-loaded shared objects (DLL/.so/.dyn files), this is usually not a big problem, because it is fairly easy to compile a modified version of the GStreamer libraries or LGPL plugins, and the application will/should just pick up and use the modified version automatically. All that is needed is for the original, LGPL-licensed source code and source code modifications to be made available, and for a way to build the libraries or plugins for the platform required (usually that will be using the build system scripts that come with GStreamer, and using the typical build environment on the system in question, but where that is not the case the needed build scripts and/or tools would need to be provided as well). IV. THINGS YOU NEED TO DO * You must tell users of your application that you are using LGPL-licensed software, which LGPL-licensed software exactly, and you must provide them with a copy of the license so they know their rights under the LGPL. * You must provide (on request) all the source code and all the changes or additions you have made to the LGPL-licensed software you are using. For GStreamer code we would recommend that the changes be provided either in form of a branch in a git repository, or as a set of "git format-patch"- style patches against a GStreamer release or a snapshot of a GStreamer git repository. The patches should ideally say what was changed and why it was changed, and there should ideally be separate patches for independent changes. * You must provide a way for users of your application to make changes to the LGPL-licensed parts of the code, and re-create a full application binary with the changes (using the standard toolchain and tools of the target platform; if you are using a custom toolchain or custom tools you must provide these and document how to use them to create a new application binary). Note that this of course does not mean that the user is allowed to re-distribute the changed application. Nor does it mean that you have to provide your proprietary source code - it is sufficient to provide a ready-made compiled object file that can be relinked into an application binary with the re-compiled LGPL components. V. THINGS TO LOOK OUT FOR While most GStreamer plugins and the libraries they depend on are licensed under the LGPL or even more permissive licenses, that is not the case for all plugins and libraries used, esp. those in the gst-plugins-ugly or some of those in the gst-plugins-bad set of plugins. When statically linking proprietary code, care must be taken not to statically link plugins or libraries that are licensed under less permissive terms than the LGPL, such as e.g. GPL-licensed libraries. VI. SPECIAL CONSIDERATIONS FOR SPECIFIC USE-CASES 1. Proprietary GStreamer/GLib-based Application On iOS Let's assume an individual or a company wants to distribute a proprietary iOS application that is built on top of GStreamer and GLib through Apple's App Store. At the time of writing the Apple iPhone developer agreement didn’t allow the bundling of shared libraries, so distributing a proprietary iOS application with shared libraries is only possible using distribution mechanisms outside of the App Store and/or only to jailbroken devices, a prospect that may not appeal to our individual or company. So the only alternative then is to link everything statically, which means the obligations mentioned above come into play. 2. Example: Jabber on iOS Tandberg (now Cisco) created a Jabber application for iOS, based on GStreamer. On request they provided an LGPL compliance bundle in form of a zip file, with roughly the following contents: buildapp.sh readme.txt Jabber/Jabber-Info.plist Jabber/libip.a [236MB binary with proprietary code] Jabber/main.mm Jabber/xcconfig/Application.xcconfig Jabber/xcconfig/Debug.xcconfig Jabber/xcconfig/Release.xcconfig Jabber/xcconfig/Shared.xcconfig Jabber/Resources/*.lproj/Localizable.strings Jabber/Resources/{Images,Audio,Sounds,IB,Message Styles,Emoticons,Fonts}/* Jabber/Resources/* Jabber.xcodeproj/project.pbxproj Jabber.xcodeproj/project.xcworkspace/contents.xcworkspacedata opensource/build/config.site opensource/build/m4/movi.m4 opensource/build/scripts/clean-deps.sh opensource/build/scripts/fixup-makefile.sh opensource/build/scripts/MoviMaker.py opensource/build.sh opensource/env.sh opensource/Makefile opensource/external/glib/* opensource/external/gstreamer/{gstreamer,gst-plugins-*}/* opensource/external/openssl/* opensource/external/proxy-libintl/* opensource/toolchain/darwin-x86/bin/{misc autotoools,m4,glib-mkenums,glib-genmarshal,libtool,pkg-config,etc.} opensource/toolchain/darwin-x86/share/{aclocal,aclocal-1.11,autoconf,automake-1.11,libtool}/* opensource/toolchain/darwin-x86/share/Config.pm opensource/toolchain/darwin-x86/share/Config.pm.movi.in patches/glib/glib.patch patches/gst-plugins-bad/gst-plugins-bad.patch patches/gst-plugins-base/gst-plugins-base.patch patches/gst-plugins-good/gst-plugins-good.patch patches/gstreamer/gstreamer.patch patches/openssl/openssl.patch readme.txt starts with "This Readme file describes how to build the Cisco Jabber for iPad application. You need to install Xcode, but the final package is built by running buildapp.sh." and describes how to build project, prerequisites, the procedure in detail, and a "How to Include Provisioning Profile Manually / Alternate Code Signing Instructions" section. 3. Random Links Which May Be Of Interest [0] http://multinc.com/2009/08/24/compatibility-between-the-iphone-app-store-and-the-lgpl/