I'm not having that problem.
Are you using the ffmpeg.exe file that I provided? Are you using a Windows OS? XAMPP?
Can you post the URLs of any videos that are not converting for you?
Are you able to play the video at "videos/1342856867_500a5ea3425531.60843462.flv"? If you can't play the video, then either the file is corrupt or cURL is not downloading the video correctly.