[FFmpeg-user] Image extraction broken with ffmpeg, but not with mencoder. How can I fix this?

[James Board]

>Did you tried -vsync 0 with above command?

I tried -vsync 0 and it worked.  ffmpeg doesn't generate additional
image files.  That's good.  I still have to redo my edits, but I guess that'okay.
 
My question is: what does -vsync do?  And, why does it work (so
I can avoid this problem in the future)?
 
Thank you for your help and I'm sorry if I was rude.