[M4IF Technotes] Reverse Decoding in DP mode

[T Sundar Murthy]

Hi,
 In case of Reverse decoding, all the intra MBs are not displayed
instead concealed (decode and discard. decoding is required to get the
next MB position).. Only inter MBs are decoded and there will not be
AC/DC prediction in case of inter MBs.section E.1.4.4.2.2 of ISO/IEC
14496-2 Second Edition.
Sundar
"Nitin Gupta--DSP, Noida" wrote:
> 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.
>
>
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