[M4IF Technotes] Reverse Decoding in DP mode

[Nitin Gupta--DSP, Noida]

Hi all,
	I have doubts regarding the reverse decoding
which we do for error resilience in the DP mode having
reversible_vlc. I want to know why the ac_pred_flag
in the DP mode having reversible_vlc should not be 
0 for all the macroblocks ? 
	If we consider a case that a video packet consist
of 3 or more macroblock rows. Then if we encounter an
error in the forward direction lets say in the first row,
we would go to the end of the video packet & would start
reverse decoding from there. Now if we once again encounter
error in that row only, then the middle row is not decoded
in the forward or the reverse direction. So now if we find
ac_pred_flag = 1 in the macroblocks that were decoded in 
the reverse direction, then how can we do AC Prediction
as there might be the case that the prediction is done
from the above row & in such a case we don't have any data for 
the above row. 
	Plz advise how to proceed in such a case as i am stuck
in its implementation & i am unable to move further forward
now.
Thanx & Regards,
Nitin Gupta.