[Ffmpeg-devel] Decoding a single MPEG2 GOP, missing 2 frames?

[Robert Ficklin]

Greetings,
                                                                       
        
I'm trying to decode the frames from a single GOP from an MPEG2 stream.
My intent is to be able to randomly seek to any GOP in a file (I have
an index of all I-frames in the file), and decode the entire GOP, one
frame at a time. The GOP size is 15, but what I see is the first 3
frames swallowed by avcodec_decode_frame without producing an output
image, the next 12 frames produce good images, and the
avcodec_decode_frame function gives me one more image when I pass it
NULL for the last input packet.  Total usuable frames = 13.  The next
random GOP I try to decode gives me an error about zombie frame being
dropped and produces
only 13 frames also.
                                                                       
        
I use av_seek_frame(..AVSEEK_FLAG_BYTE) to position the input file to
the desired GOP.  Then av_read_frame to get each frame in the GOP, and
finally avcodec_decode_frame to get each frame image. I'm also using
the CVS snapshot from May 26.
                                                                       
        
Thanks for any insight anybody may have.
                                                                       
        
Bob Ficklin