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.

#!/bin/bash

# Graceful cleanup upon CTRL-C

trap "gstd-client pipeline_delete p; exit" SIGHUP SIGINT SIGTERM

# Make sure there is no pipeline with this name already
gstd-client pipeline_delete p

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 
gstd-client pipeline_play p 

bool=true
left_=50
right_=50
up_=50
down_=50

# set the start values for the window cropped 
gstd-client element_set p crop right $right_
gstd-client element_set p crop left $left_
gstd-client element_set p crop bottom $down_
gstd-client element_set p crop top $up_
				
while [ "$bool" = true ];
do read -s -n 1 key  # read from the keyboard
	case $key in
		'a') 
			echo "left"
			# Use "A" key move to the left side 
			if [ $left_ -gt 0 ]
				then
				left_=$((left_ - 5))
				right_=$((right_ + 5))
				gstd-client element_set p crop right $right_
				gstd-client element_set p crop left $left_
			fi 
			;;
		'd') 
			echo "right"
			# Use "D" key to move to the right side 
			if [ $right_ -gt 0 ]
				then
				right_=$((right_ - 5))
				left_=$((left_ + 5))
				gstd-client element_set p crop right $right_
				gstd-client element_set p crop left $left_
			fi 
			;;
		's') 
			echo "down"
			# Use "S" key to move to the bottom side 
			if [ $down_ -gt 0 ]
				then
				up_=$((up_ + 5))
				down_=$((down_ - 5))
				gstd-client element_set p crop bottom $down_
				gstd-client element_set p crop top $up_
			fi 
			;;
		'w') 
			echo "up"
			# Use "W" key to move to the top side 
			if [ $up_ -gt 0 ]
				then
				down_=$((down_ + 5))
				up_=$((up_ - 5))
				gstd-client element_set p crop top $up_
				gstd-client element_set p crop bottom $down_
			fi 	
			;;			
		'x') 
			echo "zoom-out"
			# Use "X" key to Zoom out  
			if [ $up_ -gt 0 ] && [ $down_ -gt 0 ] && [ $left_ -gt 0 ] && [ $right_ -gt 0 ]
				then
				down_=$((down_ - 5))
				up_=$((up_ - 5))
				right_=$((right_ - 5))
				left_=$((left_ - 5))
				gstd-client element_set p crop top $up_
				gstd-client element_set p crop bottom $down_
				gstd-client element_set p crop right $right_
				gstd-client element_set p crop left $left_
			fi 		
			;;
		'z') 
			echo "zoom-in"
			# Use "Z" key to Zoom in  
			if [ $up_ -lt 200 ] 
				then
				down_=$((down_ + 5))
				up_=$((up_ + 5))
				right_=$((right_ + 5))
				left_=$((left_ + 5))
				gstd-client element_set p crop top $up_ 
				gstd-client element_set p crop bottom $down_
				gstd-client element_set p crop right $right_
				gstd-client element_set p crop left $left_
			fi 
			;;
		$'\e') 
			echo "Escape"
			# Use "ESC" key to exit to the application 
			break
			;;

	esac
done

To run the PTZ script type:

./PTZ.sh

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