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I am writing this command on my Ubuntu 14.04 terminal terminal

./cpp-example-facedetect lena.jpg

for obtaining the samples of Opencv but i am getting these errors.

errors. This program demonstrates the cascade recognizer. Now you can use Haar or LBP features. features. This classifier can recognize many kinds of rigid objects, once the appropriate classifier is trained. trained. It's most known use is for faces. Usage: faces.

Usage:

./facedetect [--cascade=<cascade_path> this is the primary trained classifier such as frontal face]
   [--nested-cascade[=nested_cascade_path this an optional secondary classifier such as eyes]]
   [--scale=<image scale="" greater="" or="" equal="" to="" 1,="" try="" 1.3="" for="" example="">]
scale greater or equal to 1, try 1.3 for example>]
   [--try-flip]
   [filename|camera_index]
[filename|camera_index]

see facedetect.cmd for one call: call:

./facedetect --cascade="../../data/haarcascades/haarcascade_frontalface_alt.xml" --nested-cascade="../../data/haarcascades/haarcascade_eye.xml" --scale=1.3
--scale=1.3

During execution: execution:

Hit any key to quit.
 Using OpenCV version 3.0.0-alpha
 
3.0.0-alpha
   Processing 1 lena.jpg
 Processing 2 //
2
   Failed to load OpenCL runtime
 init done 
 opengl support available 
 In capture ...
 OpenCV Error: Unspecified error (GStreamer: unable to start pipeline
) in icvStartPipeline, file /home/ashish/opencv_alpha/opencv-3.0.0-alpha/modules/videoio/src/cap_gstreamer.cpp, line 399
terminate called after throwing an instance of 'cv::Exception'
  what():  /home/ashish/opencv_alpha/opencv-3.0.0-alpha/modules/videoio/src/cap_gstreamer.cpp:399: error: (-2) GStreamer: unable to start pipeline
 in function icvStartPipeline
 
icvStartPipeline

Aborted (core dumped)dumped)

Please provide any solution for this, i am using Opencv 3.0.0 alpha version.