I am using ffmpeg to extract frames of video to JPEG from a WMV file - passing in a set time to perform the image extract, etc. This all works fine, and the command is as follows...

ffmpeg -i C:\<vid_name>.wmv -ss 00:00:20 -t 00:00:1 -s 320x240 -r 1 -f mjpeg <image_name>.jpg

To build up a storyboard of images, I submit the same command over and over again - incrementing the "time to process" by 1 minute. This is very resource hungry since every time it has to load the file, scan through it and then take the image.

Does anyone know if it is possible to get ffmpeg to load the file once, and then take images at set intervals through the file - as this would be much more efficient.

My other question is if the above is possible, I notice in the command list comments regarding motion detection - could you do the same, but instead of specifying a fixed interval, simply trigger of motion..?

All help is appreciated!!