Hi, I am posting to devel as I’m assuming that this won’t go without some changes to the code base, so please bear with me even though it may sound like a user issue at first sight:
This is about extracting images from a video file – every 10s in the following example: ffmpeg -i input.mkv -r 0.1 -s 320x132 img_%05d.jpg This is working of course, but it takes a pretty long time. Problem seems to be that the video is always fully decoded to every single frame. For a 30fps video that means 300 frames need to be decoded for every single image that I want. I’m not sure whether I’m missing something, but among all available parameters and filters I couldn’t find a way to affect input reading, like: "after one video frame (or timespan x) has been read, skip forward 10s reading the input” (I apologize, if there’s already a way to do this – at least I couldn’t find one.) I suppose the primary question about this might be “WHY?”. And this is easy to explain. Looking at the above command line: ffmpeg -i input.mkv -r 0.1 -s 320x132 img_%05d.jpg This will create 60 images for a 10 minute video. Alternate method: When I run ffmpeg 60 times in a batch file like this: ffmpeg -ss 0 -f matroska -i input.mkv -v quiet -vframes 1 -s 320x132 thumbX_0.png ffmpeg -ss 10 -f matroska -i input.mkv -v quiet -vframes 1 -s 320x132 thumbX_1.png ffmpeg -ss 20 -f matroska -i input.mkv -v quiet -vframes 1 -s 320x132 thumbX_2.png ffmpeg -ss 30 -f matroska -i input.mkv -v quiet -vframes 1 -s 320x132 thumbX_3.png ffmpeg -ss 40 -f matroska -i input.mkv -v quiet -vframes 1 -s 320x132 thumbX_4.png ffmpeg -ss 50 -f matroska -i input.mkv -v quiet -vframes 1 -s 320x132 thumbX_5.png ffmpeg -ss 60 -f matroska -i input.mkv -v quiet -vframes 1 -s 320x132 thumbX_6.png … … Those 60 ffmpeg executions are still twice as fast as the single command above. So, at least by theory, that whole process should be able to perform even faster with a single (optimized) execution instead of 60. What’s your thoughts about this? Did I make any incorrect assumptions? Thanks you very much, softworkz _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel