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