[M4IF Technotes] Request for clarifications while decoding backward using RVLC

[Ramkishor Korada]

Hi,
----- Original Message -----
From: "A.Ilangovan" <a.ilangovan   gdatech.co.in>
To: <technotes   lists.m4if.org>
Sent: Friday, May 03, 2024 10:08 PM
Subject: [M4IF Technotes] Request for clarifications while decoding backward
using RVLC
> Dear friends,
>
> 1)   For RVLC backward decoding also, we require the
>       DC values of Ref blocks "A" and "C". To be assured of these
>       Ref Blocks' DC values in the data_partitioned (DP) header,
>       only the DC VLC table must be used and AC VLC table must
>       not be used (If AC VLC table is used for DC coef, the DC is
>       treated with other AC coeffs in the texture info and would have
>      got corrupted in errors and also not available in DP header).
>
>      The safer / simpler way to ensure this is to make "intra_dc_vlc_thr"
>       equal to "0" in VOP header (ofcourse in VP header also), which
>      always forces the DC VLC table for DC coefficients of all the blocks.
>
>      To the extent I tried to confirm this from the standard, I am not
able
>      to find it. Am I missing it or it is missed in the standard? However,
>      all the test bitstreams provided by the standard has
"intra_dc_vlc_thr"
>      equals "0" in such cases. But, I don't want to infer this way, and
may
>      I request confirmation from experts? Also, if this is the true and is
> not
>      mentioned in the standard, it should be added in the amendments to
>     avoid this ambiguity.
>
    In simple profile at level 0, intra_dc_vlc_thr should be zero. Level 0
is aimed for wireless channels, where bit corruption is possible.
> 2)  This confusion can be further fuelled by E.1.4.4.2.2 (page:425) which
>      says INTRA MBs in a DP VP must be discarded even though they
>      could have been decoded!
>
>     Again, I have infered from the context that, this is applicable for
>     INTRA MBs in P-VOPs only!! Can experts confirm this also?
>     If this is also correct, one more item for amendments?
>

    Discaridng of INTRA MBs is recommendation only not normative.
> Thank you in advance
>
> A.Ilangovan
> ===========================================
>

regards,
ramkishor
Architect - Video
Multimedia Technologies Division
Emuzed India
Bangalore
www.emuzed.com