[M4IF Technotes] question about intra_dc_vlc_thr2

[tetsuo kosuge]

Dear Mr.Gautam and other MPEG-4 Experts :
Thanks to answer my question again, Mr.Gautam
Your thouhgt is reasonable,I think so.
If (Qp >= intra_dc_vlc_thr && pattern_code==0),usually think dc_coeff exist.
But I checked this sequence in microsft_vfdis_v10-990812 codec,seem the bitstream doesn't obey that sequence.
In this bitstream, <pattern_code == 0> has priority over Intra_MB.
When (Qp >= intra_dc_vlc_thr && pattern_code==0), the block doesn't have dc_coeff(say has 0 value in all coeff).
The other bitstream which does't make microsft codec obeys the same sequence.
And I read 14496-2:2001,this represents as follows:
	7.4.1.4 Intra dc coefficient decoding for the case of switched encoding
	At the VOP layer,using quantizer value as the threshold,a 3 bit code(intra_dc_vlc_thr) allows switching 
	between 2VLCs(DC Intra VLC and AC Intra VLC)when decoding DC coefficients of Intra macroblocks,see Table 
	6-21.
	NOTE	When the intra AC VLC is turned on,IntraDC coefficients are not handled separately any more,but 
	treated the same as all other coefficients.That means that a zero Intra DC coefficient will not be coded 
	but will simply increase the run for the following AC coefficients.The definitions of mcbpc and cbpy in 
	subclause 6.3.6 are changed accordingly.
 What does it(mcbpc and cbpy in subclause 6.3.6 are changed accordingly)  represents ? It is  that (CBP==1) -> (CBP==0)
 or (CBP==1) -> (CBP==0),or (Intra MB) -> (Inter MB) ? I can't judge correct sequence(for my lack of English kowledge? 
(TT) ).
 Which is sequence correct?
Bye, Tetsuo Kosuge
>Kosuge-San,
>
>intra_vlc_format is function of intra_dc_vlc_thr and qp.
>if intra_vlc_format = 1 and mbintra = 1 ==> dc value is encoded using ac
>table (table B-16).
>last need not to be zero. run is always zero for this, as this is the first
>element.
>i think, escape code should be used if it falls outside the table range.
>
>Warm Regards,
>Gautam
>
>
>>-----Original Message-----
>>From: tetsuo kosuge [mailto:kosuge   td.idc.lsi.sanyo.co.jp]
>>Sent: Friday, February 21, 2024 10:14 AM
>>To: Technotes   lists.m4if.org
>>Subject: [M4IF Technotes] question about intra_dc_vlc_thr2
>>
>>
>>Dear: MPEG-4 Experts
>>
>>Thanks to answer my previous question, Mr.Gautam.
>>I can understand.
>>
>>I have one more question.
>>If Intra MB which over Intra_dc_thr and block pattern_code == 
>>0, in this case dc_coeff is also derived from Intra VLC ?
>>If derive from Intra VLC, is always LAST and RUN 0 ?  And do 
>>exist ESC ?
>>
>>bye
>>	Tetsuo Kosuge
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