ffmpeg to capture screenshot from a video file in a fine time unit

I use ffmpeg to capture screenshot from video. Here is the command code:

ffmpeg -i /my_video_file_dir/video.flv -y -f image2 -ss 8 -sameq 开发者_JAVA技巧-t 0.001 
-s 320*240 /image_dir/screenshot.jpg

And I want to capture the screenshot at a fine time unit 8.344 for example

But it does not output screenshot image by the above command

In my test, -ss 1,1.5,2,2.5 ... works fine and others not such as 1.1,1.11

Does andbody know why it happens and how can I capture screenshot at a x.xxx time

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Try this instead:

ffmpeg -ss 00:00:01.01 -i /my_video_file_dir/video.flv -y -f image2 \
   -vcodec mjpeg -vframes 1 /image_dir/screenshot.jpg

Note that very small increments will not normally result in different images, due to lower frame rates of most videos. 0.001s increments only work with videos of 1000fps framerates :) 0.03 increments should work with a 30fps video, etc.