一步一步创建GStreamer插件(

原文地址：一步一步创建GStreamer插件(ZZ)作者：wuqiseu

1、获取创建插件的模板gst-template
http://hi.baidu.com/zhxust/blog/item/8161ab637d89ac6a0d33fa45.html

方法一： CVS
$cvs -d:pserver:[e-mail]/cvs/gstreamer login
password: ［root的密码］
$cvs -z3 -d:pserver:[e-mail]:/cvs/gstreamer co gst-template

方法二： GIT
如果没有安装git，则首先安装git:
$sudo apt-get install git-core
再获取模板： 

          
$git clone git://anongit.freedesktop.org/gstreamer/gst-template.git


2、进入目录gst-template/gst-plugin/src
$cd gst-template/gst-plugin/src
$../tools/make_element ExampleFilter

产生文件
gstexamplefilter.c gstexamplefilter.h

3、修改Makefile.am文件 （注意：是src目录下的Makefile.am）
$sudo gedit Makefile.am

plugin_LTLIBRARIES = libgstexamplefilter.la

libgstexamplefilter_la_SOURCES = gstexamplefilter.c

libgstexamplefilter_la_CFLAGS = $(GST_CFLAGS)
libgstexamplefilter_la_LIBADD = $(GST_LIBS)
libgstexamplefilter_la_LDFLAGS = $(GST_PLUGIN_LDFLAGS)
libgstexamplefilter_la_LIBTOOLFLAGS = --tag=disable-static

noinst_HEADERS = gstexamplefilter.h

总共有七行


4、导入PKG_CONFIG_PATH环境变量，在命令行输入：

$export PKG_CONFIG_PATH=/usr/lib/pkgconfig


5、进入目录gst-template/gst-plugin,修改文件autogen.sh
进入上一层目录
$cd.. 
编辑autogen.sh文件：
$sudo gedit autogen.sh

如果是通过CVS获取的模板，则修改原来的
srcfile=src/main.c
为新的：
srcfile=src/gstexamplefilter.c

如果是通过GIT获取的模板，则在autogen.sh的开始添加：
srcfile=src/gstexamplefilter.c

6、运行autogen.sh,产生Makefile文件

$./autogen.sh

7、开始安装：
$./configure
$make
$sudo make install

再进入src子目录中
$cd src

用ls -a查询会有.libs目录产生
（注意： .libs 为隐藏目录）
进入.libs
$cd .libs
$ls -a
会发现里面产生了

libgstexamplefilter.la
libgstexamplefilter.so

8、将插件加入到gstreamer库中
把libgstexamplefilter.la
libgstexamplefilter.so
这两个文件拷贝到系统目录中： /usr/lib/gstreamer-0.10

$sudo cp libgstexamplefilter.la /usr/lib/gstreamer-0.10/libgstexamplefilter.la
$sudo cp libgstexamplefilter.so /usr/lib/gstreamer-0.10/libgstexamplefilter.so

如果gstreamer无法扫描到新加入的plugin，可能是因为路径设置不正确(GST_PLUGIN_PATH环境变量)
    

  用gst-inspect命令来查看plugin时，会建立一个cache文件：如在X86上是
     $HOME/.gstreamer-0.10/registry.x86_64.bin
  如果有新的plugin加入，可能需要先删除这个cache文件，再重新运行gst-inspect,否则不会把新的plugin
  扫描到cache中。

 几个重要的环境变量：
   1:GST_PLUGIN_SCANNER
  
  env = g_getenv ("GST_PLUGIN_SCANNER");  //设置gst-plugin_scanner这个命令的路径

  2. GST_PLUGIN_PATH
  
  plugin_path = g_getenv ("GST_PLUGIN_PATH"); //plugin的搜索路径
  g_warning ("External plugin loader failed. This most likely means that "
          "the plugin loader helper binary was not found or could not be run. "
          "%s", (g_getenv ("GST_PLUGIN_PATH") != NULL) ?
          "If you are running an uninstalled GStreamer setup, you might need "
          "to update your gst-uninstalled script so that the "
          "GST_PLUGIN_SCANNER environment variable gets set." : "");


3.GST_PLUGIN_SYSTEM_PATH
   GST_PLUGIN_SYSTEM_PATH specifies a list of plugins that are always
   loaded by default.  If not set, this defaults to the system-installed
   path, and the plugins installed in the user's home directory

  plugin_path = g_getenv ("GST_PLUGIN_SYSTEM_PATH");

  如果这个变量没有设置，default:
 
   plugin_path = g_getenv ("GST_PLUGIN_SYSTEM_PATH");
   if (plugin_path == NULL) {
    home_plugins = g_build_filename (g_get_home_dir (),
        ".gstreamer-" GST_MAJORMINOR, "plugins", NULL);
   }



 4. GST_REGISTRY_UPDATE(yes or no) ，是否重新扫描去更新cache内容
    update_env = g_getenv ("GST_REGISTRY_UPDATE")
    do_update = (strcmp (update_env, "no") != 0)


  函数调用：
    init_post()->gst_update_registry()->ensure_current_registry()->gst_registry_binary_read_cache
                                                                 ->scan_and_update_registry()
    ->读环境变量GST_PLUGIN_PATH->gst_registry_scan_path_internal()
    ->读环境变量GST_PLUGIN_SYSTEM_PATH-> gst_registry_scan_path_internal() （从目录下去读文件)               


检查插件：
$gst-inspect examplefilter

如果显示了插件的信息，那么插件就创建好了


(2) Gst good/ugly/bad 库中的plugin的列表
    http://gstreamer.freedesktop.org/documentation/plugins.html

    关于whitelist和blacklist(黑名单)
     在plugin库中，有些plugin的license是blacklist的：
          if (strcmp (plugin->desc.license, "BLACKLIST") == 0)
                  plugin->flags |= GST_PLUGIN_FLAG_BLACKLISTED;

     但是BLACKLIST并不是开放给用户设置的，而是gstreamer里面自己使用的。含义是说如果这个plugin 
     加载失败时，那么就加入到blacklist中，下次不需要去扫描了，用户也不能去使用。
     这种plugin在scan时会进入blacklist的plugin list中，在下次扫描时不会去扫描这些blacklist。
       exchange_packets()->read_one（）-> handle_rx_packet(payloadLength)->plugin_loader_create_blacklist_plugin（）

   代码：
     if (entry != NULL) {
       
        plugin_loader_create_blacklist_plugin (l, entry);//plugin->desc.license = "BLACKLIST";
        l->got_plugin_details = TRUE;
      }

    如果要查看为什么加载plugin会失败：https://bugzilla.gnome.org/show_bug.cgi?id=627102
      plugins are blacklisted when there's an error loading them. You can check what went wrong by removing your registry (~/.gstreamer-0.10/registry*) and then running:
      GST_DEBUG=2,GST_PLUGIN_LOADING:5,GST_REGISTRY:5 gst-inspect-0.10


     上面这些参数是设置debug系统：
       _gst_debug_init()

(3) Gstreamer中的几个命令使用
    http://linux.about.com/library/cmd/blcmdl1_gst-inspect.htm
    http://www.opensolarisforum.org/man/man1/gst-inspect.html

    gst-inspect:      

gst-inspect prints information about available GStreamer plugins, information about a particular plugin, or information about a particular element.

If no element or plugin argument is specified, gst-inspect prints a list of all plugins and elements. If an element or plugin argument is specified, gst-inspectprints information about that element or plug-in. If a given argument is valid as either an element or a plugin, gst-inspect treats the argument as an element, by default.

OPTIONS

The following options are supported by gst-inspect:

-a, --print-all Print all elements.

--version Print GStreamer version number.

gst-std-options Standard options available for use with most GStreamer applications. See gst-std-options(5) for more information.

OPERANDS

The following operands are supported:

element Name of an element.

plugin Name of a plugin.

EXAMPLES

Example 1: Displaying Information About a Plugin:

example% gst-inspect alaw Plugin Details: Name: alaw Description: ALaw audio conversion routines Filename: /usr/lib/gstreamer-0.10/libgstalaw.so Version: 0.10.3 License: LGPL Source module: gst-plugins-good Binary package: GStreamer Good Plug-ins source release Origin URL: Unknown package origin alawdec: A Law audio decoder alawenc: A Law audio encoder 2 features: +-- 2 elements

 

    gst-launch:
      

gst-launch builds and runs basic GStreamer pipelines.

In simple form, a pipeline-description is a list of elements separated by exclamation marks (!). Properties can be appended to elements, in the form property=value.

For a complete description of possible values for pipeline-description, see the section Pipeline Description below or consult the GStreamer documentation.

Please note that gst-launch is primarily a debugging tool for developers and users. You should not build applications on top of it. For applications, use the gst_parse_launch() function of the GStreamer API as an easy way to construct pipelines from pipeline descriptions.

OPTIONS

The following options are supported by gst-launch:

-X, --exclude=type1,type2,... Do not output status information of specified type.

-f, --no-fault Do not install a fault handler.

-o, -output-=file Save XML representation of pipeline to file, then exit.

-t, --tags Output tags, also known as metadata.

-T, --trace Print memory allocation trace, if enabled at compile time.

-v, --verbose Output status information and property notifications.

--version Print GStreamer version number.

gst-std-options Standard options available for use with most GStreamer applications. See gst-std-options(5) for more information.

EXTENDED DESCRIPTION

    Pipeline Description

A pipeline consists elements and links. Elements can be put into bins of different sorts. Elements, links and bins can be specified in a pipeline description in any order.

    Elements

elementtype [property1 ...]

Creates an element of type elementtype and sets the properties.

    Properties

property=value ...

Sets the property to the specified value. You can use gst-inspect(1) to find out about properties and allowed values of different elements.

Enumeration properties can be set by name, nick or value.

    Bins

[bintype.] ( [property1 ...] pipeline-description )

Specifies that a bin of type bintype is created and the given properties are set. Every element between the braces is put into the bin. Please note the dot that has to be used after the bintype. You will almost never need this functionality, it is only really useful for applications using the gst_launch_parse() API with ’bin’ as bintype. That way it is possible to build partial pipelines instead of a full-fledged top-level pipeline.

    Links

[[srcelement].[pad1,...]] ! [[sinkelement].[pad1,...]] [[srcelement].[pad1,...]] !caps ! [[srcelement].[pad1,...]]

Links the element with name srcelement to the element with name sinkelement, using the caps specified in caps as a filter. Names can be set on elements with the name property. If the name is omitted, the element that was specified directly in front of or after the link is used. This works across bins. If a padname is given, the link is done with these pads. If no pad names are given all possibilities are tried and a matching pad is used. If multiple padnames are given, both sides must have the same number of pads specified and multiple links are done in the given order. So the simplest link is a simple exclamation mark, that links the element to the left of it to the element right of it.

    Caps

mimetype [, property[, property ...]]] [; caps[; caps ...]]

Creates a capability with the given mimetype and optionally with given properties. The mimetype can be escaped using " or ’. If you want to chain caps, you can add more caps in the same format afterwards.

    Properties

name[:type]=value in lists and ranges: [type=]value

Sets the requested property in capabilities. The name is an alphanumeric value and the type can have the following case-insensitive values:

o i or int for integer values or ranges

o f or float for float values or ranges

o 4 or fourcc for FOURCC values

o b, bool, or boolean for boolean values

o s, str, or string for strings

o l or list for lists

If no type was given, the following order is tried: integer, float, boolean, string. Integer values must be parsable by strtol(), floats by strtod(). FOURCC values may either be integers or strings. Boolean values are (case insensitive) yes, no, true or false and may like strings be escaped with " or ’.

Ranges are in this format: [ property, property ] Lists use this format: ( property [,property ...] )

    Pipeline Control

A pipeline can be controlled by signals. SIGUSR2 will stop the pipeline (GST_STATE_NULL); SIGUSR1 will put it back to play (GST_STATE_PLAYING). By default, the pipeline will start in the playing state. There are currently no signals defined to go into the ready or pause (GST_STATE_READY and GST_STATE_PAUSED) state expli- citely.

EXAMPLES

The examples below assume that you have the correct plugins available. In general, "sunaudiosink" can be substituted with another audio output plugin such as "esdsink", "alsasink", "osxaudiosink", or "artsdsink". Likewise, "xvimagesink" can be substituted with "ximagesink", "sdlvideosink", "osxvideosink", or "aasink". Keep in mind though that different sinks might accept different formats and even the same sink might accept different formats on different machines, so you might need to add converter elements like audioconvert and audioresample (for audio) or ffmpegcolorspace (for video) in front of the sink to make things work.

Example 1: Audio Playback

Play the WAV music file "music.wav":

example% gst-launch filesrc location=music.wav ! wavparse ! sunaudiosink

Play the mp3 music file "music.mp3":

example% gst-launch filesrc location=music.mp3 ! flump3dec ! sunaudiosink

Play the Ogg Vorbis file "music.ogg":

example% gst-launch filesrc location=music.ogg ! oggdemux ! vorbisdec ! audioconvert ! sunaudiosink

Play an mp3 file or an http stream using GNOME-VFS:

example% gst-launch gnomevfssrc location=music.mp3 ! flump3dec ! sunaudiosink

example% gst-launch gnomevfssrc location=http://domain.com/music.mp3 ! flump3dec ! sunaudiosink

Use GNOME-VFS to play an mp3 file located on an SMB server:

example% gst-launch gnomevfssrc location=smb://computer/music.mp3 ! flump3dec ! sunaudiosink

Example 2: Video Playback

Play an Ogg video file:

example% gst-launch filesrc location=video.ogg ! oggdemux ! theoradec ! ffmpegcolorspace ! xvimagesink

Example 3: Format Conversion

Convert an mp3 music file to the Ogg Vorbis format:

example% gst-launch filesrc location=music.mp3 ! flump3dec ! audioconvert ! vorbisenc ! oggmux ! filesink location=music.ogg

Convert an mp3 music file to the FLAC format:

example% gst-launch filesrc location=music.mp3 ! flump3dec ! audioconvert ! flacenc ! filesink location=test.flac

Convert a .WAV file to the Ogg Vorbis format:

example% gst-launch filesrc location=music.wav ! wavparse ! audioconvert ! vorbisenc ! oggmux ! filesink location=music.ogg

Example 4: Recording Audio

Record sound from your audio input and encode it into an Ogg file:

example% gst-launch sunaudiosrc ! audioconvert ! vorbisenc ! oggmux ! filesink location=music.ogg

Example 5: Compact Disk (CDDA)

Play track number 3 from compact disc:

example% gst-launch cddasrc track=3 ! sunaudiosink

Play track number 5 from compact disc:

example% gst-launch cdda://5 ! sunaudiosink

Example 6: Diagnostic

Generate a null stream and ignore it:

example% gst-launch fakesrc ! fakesink

Generate a pure tone to test the audio output:

example% gst-launch audiotestsrc ! sunaudiosink

Generate a familiar test pattern to test the video output:

example% gst-launch videotestsrc ! xvimagesink

Generate a familiar test pattern to test the video output:

example% gst-launch videotestsrc ! ximagesink

Example 7: Automatic Linking

You can use the decodebin element to automatically select the right elements to get a working pipeline.

Play any supported audio format:

example% gst-launch filesrc location=musicfile ! decodebin ! sunaudiosink

Play any supported video format with video and audio output. Threads are used automatically.

example% gst-launch filesrc location=videofile ! decodebin name=decoder decoder. ! queue ! audioconvert ! audioresample ! osssink decoder. ! ffmpegcolorspace ! xvimagesink

To make this even easier, you can use the playbin element:

example% gst-launch playbin uri=file:///home/joe/foo.avi

Example 8: Filtered Connections

These examples show how to use filtered capabilities.

Show a test image and use the YUY2 or YV12 video format for this:

example% gst-launch videotestsrc ! video/x-raw-yuv,format=urcc)YUY2;video/x-raw-yuv,format=urcc)YV12 ! xvimagesink

Record audio and write it to a .wav file. Force usage of signed 16 to 32 bit samples and a sample rate between 32kHz and 64KHz:

example% gst-launch sunaudiosrc ! ’audio/x-raw-int,rate=[32000,64000],width=[16,32],depth={16,24,32},signed=(boolean)true’ ! wavenc ! filesink location=recording.wav更加详细的信息查看：   http://gstreamer.freedesktop.org/documentation/