[XviD-devel] Decoded only 30 bytes from an I-frame - what causes it?

[Yong, Chee Yeew]

Hello all,

I am experiencing a bizarre effect from the Xvid decoder. Whenever I try to
decode an I-frame (by calling xvid_decore), I first get 30 bytes of decoded
'data', and then the rest of the I-frame gets decoded (the next time I call
xvid_decore). 
To make it clearer, I have a buffer that keeps all the frames that are to be
decoded. Whenever an I-frame is encountered, xvid_decore decodes only the
first 30 bytes. I then shift the buffer forward by 30 bytes, leaving the
rest of the I-frame in the buffer. The next time I call xvid_decore, only
then the rest of the I-frame gets decoded.
This does not occur on P-frames. There are no B-frames in my stream.

Is this normal?
What is the significance of the 30 bytes value?

Any pointers *at all* would be welcome.

Cheers,
Chee