It is just a pain in the ass if you cannot get any work done because you have to constantly check if the image of a webcam has changed. Therefore I wrote a shell script that downloads the webcam images and puts them together as a video.
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\nWhat the scrip does is the following:<\/p>\n
Now let’s give some credit where it is due: I put the code into two functions. The first takes for arguments:<\/p>\n First we make sure that the directory where we store the images exists. Then we figure out what the file name of the latest downloaded image is. We can then download the image with curl or wget. To compare the two files (the latest and the just downloaded) we compute the md5 checksum and compare them. If the do not match we rename the downloaded file by giving it a timestamp as a file name and then call the second function to create the video. Now the second function creates the video from the image files. It takes the name of the video file as an argument. I choose the ffmpeg approach since it did work better for me and might work better on a NAS.<\/p>\n The video is created with a frame rate of one frame per second. If you want to display the same image over several seconds you have to input it several times. The variable DURATION defines how many times. The images are copied into the temporary video directory. The file name is changed to consecutive numbering with five digits starting with 0. The tricky part is the counting: The file name is a string so you have to evaluate the expression of adding 1 to the numeric file name and then reformatting it as a five digit string. To install this a a cronjob issue<\/p>\n on the console and add this line<\/p>\n You will want to apply the correct path to your script. This line executes the script every ten minutes and throws away all output. If the images on the URL are replaced regularly you are doing good in choosing the same interval here.
\nDownloading the image can be done with either wget or curl. However the file must be renamed do avoid overriding: Curl for grabbing webcam pics in succession?<\/a>
\nBasically there are three ways to create a movie from images. Two are described in Making movies from image files using ffmpeg\/mencoder<\/a>. The third<\/a> did not work for me but this may because I use Ubuntu Gnome. On a KDE desktop it might work. This solution however only works with a desktop an cannot be run on a server or a NAS.
\nThe iterative aspect of the execution of the script I solved with a cron job<\/a>.<\/p>\n\n
\r\ndownloadAndCreateMovie(){\r\n\tSTORE_PATH=$2\r\n\tURL=$1\r\n\r\n\tif [ ! -d $STORE_PATH ]\r\n\tthen\r\n\t\tmkdir $STORE_PATH\r\n\tfi\r\n\tcd $STORE_PATH\r\n\tPREFIX=$3\r\n\tLASTFILE=`ls -Atr *.jpg | tail -1`\r\n\tFILENAME=$4\r\n\r\n\r\n#\tcurl -O $URL\r\n\twget -q $URL\r\n\r\n\tMD5LAST=`md5sum -b $LASTFILE | sed 's: :\\n:g' | head -1`\r\n\r\n\tMD5CUR=`md5sum -b $FILENAME | sed 's: :\\n:g' | head -1`\r\n\r\n\tif test $MD5LAST != $MD5CUR\r\n\tthen\r\n\t\tcp -v $FILENAME `date +\"%y%m%d-%H%M%S\"`.jpg\r\n\t\timages2movie $PREFIX\r\n\tfi\r\n\trm $FILENAME\r\n}\r\n<\/pre>\n
\nThis function has some drawbacks:<\/p>\n\n
\r\nimages2movie(){\r\n\tMOVIE_NAME=\"movie\"\r\n\tMOVIE_NAME=$1\r\n\tDURATION=3\r\n\tmkdir movie\r\n\tFILECOUNTER=`printf \"%05d\" 0`\r\n\tfor file in `ls`\r\n\tdo\r\n\t\tfor (( i = 0 ; i < = $DURATION; i++ ))\r\n\t\tdo\r\n\t\t\tcp $file movie\/$FILECOUNTER.jpg\r\n\t\t\tFILECOUNTER=`expr $FILECOUNTER + 1`\r\n\t\t\tFILECOUNTER=`printf \"%05d\" $FILECOUNTER`\t\r\n\t\tdone\r\n\tdone\r\n\trm $MOVIE_NAME.mp4\r\n\tffmpeg -r 1 -b 1800 -s svga -i movie\/%05d.jpg $MOVIE_NAME.mp4\r\n\trm -rf movie\r\n}\r\n<\/pre>\n
\nThe next thing is to create the video from the sample images. The parameter -r specifies the frames per second. The parameter -b defines the bitrate. The parameter -s defines the output format. Here you will want to select a format that matches the format of the images for best quality. The parameter -i defines the input using the same expression as the file name. The last parameter is the output file name.
\nBasically that's it. Therefore the call would look like this:<\/p>\n\r\nSTORE_PATH=~\/Pictures\/kronplatz\/Marchner\r\nURL=http:\/\/www.kronplatz.com\/_webcam\/70\/webcam7.jpg\r\ndownloadAndCreateMovie $URL $STORE_PATH Marchner webcam7.jpg\r\n<\/pre>\n
\r\ncrontab -e\r\n<\/pre>\n
\r\n*\/10 * * * * \/home\/andi\/bin\/downloadImage.sh > \/dev\/null 2>&1\r\n<\/pre>\n
\nWhen closing the editor the temporary file will be stored and installed as cron job.<\/p>\n