http://sdkdocs.roku.com/display/sdkdoc/ ... leCreationRoku recommends using ffmpeg. I prefer to use VirtualDub with an mpeg plugin to extract the images - as it's more accurate on timing.
...the stated ffmpeg command for generating graphics does kind of work - I suppose it depends on your source video file. Most of the time for me it generates 3 of the same image and then an image from ~8 seconds, followed by 19 seconds, followed by 27 seconds, etc - it is fast, can be batched to do hundreds of videos, etc etc - but it is truly sloppy in the results, requiring files to be renamed after it's done, and so on. I tried builds of ffmpeg going back from the latest and 'greatest' to versions in 2008 and all exhibit this problem.
The way I resolved it was using VirtualDub and a plugin to allow loading MP4 files. The 'ffmpeg input driver' mentioned here -
http://www.donsalva.com/2011/07/03/how- ... virtualduballows that. So you can load your mp4 into virutaldub, go to video/framerate and select "decimate by". If your video is 25fps then decimate by would be 250. If 23.976 then 240 would be 'close enough' - 29.976 would be 300...
Then go to Video/Filters and add 'resize' to set your image dimensions (320x240) , and then file/export image sequence.
It starts the numbering at 0, you can set the number of leading 0's, defaults to JPG and you can set quality, and it's faster than ffmpeg (at least it seems faster to me). Then you can run the standard biftool, python, ruby script or whatever you use for the images and it turns out accurate results.