GStreamer Daemon - Digital PTZ

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Digital PTZ

Digital PTZ is based on 3 parameters: input resolution, output resolution, and properties (pan, tilt, and zoom). the properties can be described as following:

Zoom

The zoom can reduce the resolution of the output image and the output image can be crop or a complete image, taking the input image as a complete reference. Follow the picture below which explains how it works:

Pan-Tilt

• Pan: Indicates the movement left or right in the image coordinate.
• Tilt: Indicates the movement top or bottom in the image coordinate.

Follow picture explain how works Pan and tilt:

Using Gstd

For the PTZ example, we will use Gstd that allows us to change the values of any property of the elements in the pipeline while the pipeline is running, in our case is very useful that feature. The next example script can move a cropped window around a video playback, also the window can be zoom-in and zoom out.

how to use the example:

* Use A for a left move. 
* Use D for a right move. 
* Use W for a up move. 
* Use S for a down move.
* Use Z to zoom-in.
* Use X to zoom-out.
* Use ESC to exit on the example.  

  1 #!/bin/bash
  2 
  3 # Graceful cleanup upon CTRL-C
  4 
  5 trap "gstd-client pipeline_delete p; exit" SIGHUP SIGINT SIGTERM
  6 
  7 # Make sure there is no pipeline with this name already
  8 gstd-client pipeline_delete p
  9 
 10 gstd-client pipeline_create p videotestsrc is-live=true ! capsfilter caps=video/x-raw,width=640,height=480 ! videocrop name=crop ! videoscale ! capsfilter caps=video/x-raw,width=320,height=240 ! autovideosink 
 11 gstd-client pipeline_play p 
 12 
 13 bool=true
 14 left_=50
 15 right_=50
 16 up_=50
 17 down_=50
 18 
 19 # set the start values for the window cropped 
 20 gstd-client element_set p crop right $right_
 21 gstd-client element_set p crop left $left_
 22 gstd-client element_set p crop bottom $down_
 23 gstd-client element_set p crop top $up_
 24 				
 25 while [ "$bool" = true ];
 26 do read -s -n 1 key  # read from the keyboard
 27 	case $key in
 28 		'a') 
 29 			echo "left"
 30 			# Use "A" key move to the left side 
 31 			if [ $left_ -gt 0 ]
 32 				then
 33 				left_=$((left_ - 5))
 34 				right_=$((right_ + 5))
 35 				gstd-client element_set p crop right $right_
 36 				gstd-client element_set p crop left $left_
 37 			fi 
 38 			;;
 39 		'd') 
 40 			echo "right"
 41 			# Use "D" key to move to the right side 
 42 			if [ $right_ -gt 0 ]
 43 				then
 44 				right_=$((right_ - 5))
 45 				left_=$((left_ + 5))
 46 				gstd-client element_set p crop right $right_
 47 				gstd-client element_set p crop left $left_
 48 			fi 
 49 			;;
 50 		's') 
 51 			echo "down"
 52 			# Use "S" key to move to the bottom side 
 53 			if [ $down_ -gt 0 ]
 54 				then
 55 				up_=$((up_ + 5))
 56 				down_=$((down_ - 5))
 57 				gstd-client element_set p crop bottom $down_
 58 				gstd-client element_set p crop top $up_
 59 			fi 
 60 			;;
 61 		'w') 
 62 			echo "up"
 63 			# Use "W" key to move to the top side 
 64 			if [ $up_ -gt 0 ]
 65 				then
 66 				down_=$((down_ + 5))
 67 				up_=$((up_ - 5))
 68 				gstd-client element_set p crop top $up_
 69 				gstd-client element_set p crop bottom $down_
 70 			fi 	
 71 			;;			
 72 		'x') 
 73 			echo "zoom-out"
 74 			# Use "X" key to Zoom out  
 75 			if [ $up_ -gt 0 ] && [ $down_ -gt 0 ] && [ $left_ -gt 0 ] && [ $right_ -gt 0 ]
 76 				then
 77 				down_=$((down_ - 5))
 78 				up_=$((up_ - 5))
 79 				right_=$((right_ - 5))
 80 				left_=$((left_ - 5))
 81 				gstd-client element_set p crop top $up_
 82 				gstd-client element_set p crop bottom $down_
 83 				gstd-client element_set p crop right $right_
 84 				gstd-client element_set p crop left $left_
 85 			fi 		
 86 			;;
 87 		'z') 
 88 			echo "zoom-in"
 89 			# Use "Z" key to Zoom in  
 90 			if [ $up_ -lt 200 ] 
 91 				then
 92 				down_=$((down_ + 5))
 93 				up_=$((up_ + 5))
 94 				right_=$((right_ + 5))
 95 				left_=$((left_ + 5))
 96 				gstd-client element_set p crop top $up_ 
 97 				gstd-client element_set p crop bottom $down_
 98 				gstd-client element_set p crop right $right_
 99 				gstd-client element_set p crop left $left_
100 			fi 
101 			;;
102 		$'\e') 
103 			echo "Escape"
104 			# Use "ESC" key to exit to the application 
105 			break
106 			;;
107 
108 	esac
109 done

To run the PTZ script type:

./PTZ.sh

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