[FFmpeg-user] How to grab a jpg thumb image?

[kadin 320]

I am trying to grab a frame of video and convert it to a jpg thumb image.
I am only seccessful at coverting it to a png thumb.
I tried putting the word jpg and jpeg in the exec()
and making sure the file ext. is jpg or jpeg, but I can't get it to work.
What am I doing wrong? Thanks.

exec("$ffmpegPath -y -i $srcFile -vframes 1 -ss 00:00:03 -an -vcodec png -f
rawvideo -s 110x90 $destThumb");