今天在研究AR_ToolKit，它需要搭建OpenCV的環境。於是下載了OpenCV的原始碼進行編譯（下載方法就是直接git克隆git clone https://github.com/opencv/opencv）。

編譯opencv的過程中，一開始都一帆風順，不過後來遇到了以下問題：

[ 49%] Building CXX object modules/videoio/CMakeFiles/opencv_videoio.dir/src/cap_gstreamer.cpp.o
In file included from /usr/include/gstreamer-0.10/gst/pbutils/encoding-profile.h:29:0,
                 from /home/leon/open_source/opencv/modules/videoio/src/cap_gstreamer.cpp:69:
/usr/include/gstreamer-0.10/gst/pbutils/gstdiscoverer.h:35:9: error: ‘GstMiniObjectClass’ does not name a type
 typedef GstMiniObjectClass GstDiscovererStreamInfoClass;
         ^
/usr/include/gstreamer-0.10/gst/pbutils/gstdiscoverer.h:83:9: error: ‘GstMiniObjectClass’ does not name a type
 typedef GstMiniObjectClass GstDiscovererContainerInfoClass;
         ^
/usr/include/gstreamer-0.10/gst/pbutils/gstdiscoverer.h:104:9: error: ‘GstMiniObjectClass’ does not name a type
 typedef GstMiniObjectClass GstDiscovererAudioInfoClass;
         ^
/usr/include/gstreamer-0.10/gst/pbutils/gstdiscoverer.h:129:9: error: ‘GstMiniObjectClass’ does not name a type
 typedef GstMiniObjectClass GstDiscovererVideoInfoClass;
         ^
/usr/include/gstreamer-0.10/gst/pbutils/gstdiscoverer.h:159:9: error: ‘GstMiniObjectClass’ does not name a type
 typedef GstMiniObjectClass GstDiscovererSubtitleInfoClass;
         ^
/usr/include/gstreamer-0.10/gst/pbutils/gstdiscoverer.h:202:9: error: ‘GstMiniObjectClass’ does not name a type
 typedef GstMiniObjectClass GstDiscovererInfoClass;
         ^
In file included from /home/leon/open_source/opencv/modules/videoio/src/cap_gstreamer.cpp:69:0:
/usr/include/gstreamer-0.10/gst/pbutils/encoding-profile.h:47:9: error: ‘GstMiniObjectClass’ does not name a type
 typedef GstMiniObjectClass GstEncodingProfileClass;
         ^
/usr/include/gstreamer-0.10/gst/pbutils/encoding-profile.h:66:9: error: ‘GstEncodingProfileClass’ does not name a type
 typedef GstEncodingProfileClass GstEncodingContainerProfileClass;
         ^
/usr/include/gstreamer-0.10/gst/pbutils/encoding-profile.h:85:9: error: ‘GstEncodingProfileClass’ does not name a type
 typedef GstEncodingProfileClass GstEncodingVideoProfileClass;
         ^
/usr/include/gstreamer-0.10/gst/pbutils/encoding-profile.h:104:9: error: ‘GstEncodingProfileClass’ does not name a type
 typedef GstEncodingProfileClass GstEncodingAudioProfileClass;
         ^
/home/leon/open_source/opencv/modules/videoio/src/cap_gstreamer.cpp: In member function ‘virtual bool GStreamerCapture::grabFrame()’:
/home/leon/open_source/opencv/modules/videoio/src/cap_gstreamer.cpp:268:57: error: ‘gst_app_sink_pull_sample’ was not declared in this scope
     sample = gst_app_sink_pull_sample(GST_APP_SINK(sink));
                                                         ^
/home/leon/open_source/opencv/modules/videoio/src/cap_gstreamer.cpp: In member function ‘virtual bool CvVideoWriter_GStreamer::open(const char*, int, double, CvSize, bool)’:
/home/leon/open_source/opencv/modules/videoio/src/cap_gstreamer.cpp:1515:25: error: ‘GST_VIDEO_FORMAT_ENCODED’ was not declared in this scope
         input_pix_fmt = GST_VIDEO_FORMAT_ENCODED;
                         ^
/home/leon/open_source/opencv/modules/videoio/src/cap_gstreamer.cpp: In member function ‘virtual bool CvVideoWriter_GStreamer::writeFrame(const IplImage*)’:
/home/leon/open_source/opencv/modules/videoio/src/cap_gstreamer.cpp:1686:26: error: ‘GST_VIDEO_FORMAT_ENCODED’ was not declared in this scope
     if (input_pix_fmt == GST_VIDEO_FORMAT_ENCODED) {
                          ^
make[2]: *** [modules/videoio/CMakeFiles/opencv_videoio.dir/src/cap_gstreamer.cpp.o] 錯誤 1
make[1]: *** [modules/videoio/CMakeFiles/opencv_videoio.dir/all] 錯誤 2
make: *** [all] 錯誤 2
 

提取其中一句來看看：

/usr/include/gstreamer-0.10/gst/pbutils/gstdiscoverer.h:202:9: error: ‘GstMiniObjectClass’ does not name a type
 typedef GstMiniObjectClass GstDiscovererInfoClass;

很明顯，與gstreamer-0.10有關。再去分析下CMakeList檔案，以gstreamer為關鍵詞查詢，發現有如下命令：

OCV_OPTION(WITH_FFMPEG         "Include FFMPEG support"                      ON   IF (NOT ANDROID AND NOT IOS AND NOT WINRT) )
OCV_OPTION(WITH_GSTREAMER      "Include Gstreamer support"                   ON   IF (UNIX AND NOT ANDROID) )
OCV_OPTION(WITH_GSTREAMER_0_10 "Enable Gstreamer 0.10 support (instead of 1.x)"                              OFF )
OCV_OPTION(WITH_GTK            "Include GTK support"                         ON   IF (UNIX AND NOT APPLE AND NOT ANDROID) )
 

可以看出，這就明確表示了cmakelist必須依賴於gstreamer-0.10。這裡順便介紹一下gstreamer-0.10，根據百度百科，GStreamer是用來構建流媒體應用的開源多媒體框架(framework)，其目標是要簡化音/視訊應用程式的開發，目前已經能夠被用來處理像 MP3、Ogg、MPEG1、MPEG2、AVI、Quicktime 等多種格式的多媒體資料。在linux中，進行視訊處理的時候，有時候我們需要讀入各種各樣格式的視訊。在沒有相應的解碼器的時候，我們是無法正確讀入資料的，所以要正確安裝gstreamer才能實現各種格式視訊的正確讀取。

於是，乖乖的安裝吧：

sudo apt-get install libgstreamer1.0-dev  libgstreamer-plugins-base1.0-dev
 

裝完，再編譯，一切OK啦！