[Ffmpeg-devel] first frame wrong

[Ignazio Castrogiovanni]

I've made a wrapper of the last ffmpeg for using in my program. I send all
the parameters to a function that replies the ffmpeg.c and I obtain the same
results as I was just using the ffmpeg.
But I still have a problem about the first frame of some file...
If I extract the first image of a video it looks damaged
If I extract a video from frame 0 to 30 for example (-vframes 31) I get a
video formed by 31 frames but starting from frame 2 and ending to the frame
32 (fr 0 and fr 1 skipped).
Is there some -tag  that I can use to solve this problem?
If there's no tag, How can I do to put a right frame (frame n. 3 for
example) in the first 2 position and have my 31 frames compose by frame (n3
n3 n3 n4 n5 n6 ... n30)?
Thanks in advance!!