[FFmpeg-devel] Help!!!B picture before any references, skipping&&decode_slice_header error&&no frame!

[Cheng TaoTRS]

-hi,all- 
	i am using ffmpeg to extract frames of vedio files. 
	today, i encountered a problem. when i decoding a avi file, the
following is the warning information:

[h264 @ 0xb7e57830]B picture before any references, skipping
[h264 @ 0xb7e57830]decode_slice_header error
[h264 @ 0xb7e57830]no frame!
[h264 @ 0xb7e57830]B picture before any references, skipping
[h264 @ 0xb7e57830]decode_slice_header error
[h264 @ 0xb7e57830]no frame!
[h264 @ 0xb7e57830]B picture before any references, skipping
[h264 @ 0xb7e57830]decode_slice_header error
[h264 @ 0xb7e57830]no frame!
[h264 @ 0xb7e57830]B picture before any references, skipping
[h264 @ 0xb7e57830]decode_slice_header error
[h264 @ 0xb7e57830]no frame!
[h264 @ 0xb7e57830]B picture before any references, skipping
[h264 @ 0xb7e57830]decode_slice_header error
[h264 @ 0xb7e57830]no frame!

what's wrong?  

the frame i obtained is very fuzzy, as if having many mosaic.

anybody help me?