[x264-devel] Regarding disabling 4x4 in JM code

[List, Peter]

________________________________

Von: mahesh k [mailto:maheswarreddy.k at gmail.com] 
Gesendet: Dienstag, 7. August 2007 14:24
An: Mailing list for x264 developers
Betreff: Re: [x264-devel] Regarding disabling 4x4 in JM code

 

Dear peter,
I am talking about decoder only. I will explain u my problem more
clearly.

Right now our decoder works properly with our encoder. Now we need to
make this decoder standardised in the sense that it should accept any
other bitstream(for example i want to decode JM encoders output with my
decoder). 

After reading the syntax elements as per baseline standard I need to
check whether this is implemented or not in my decoder and return the
error still needs to be implemented. the intent was that the code
shouldnot crash in such situations instead return proper error code. 

Obviously you will need to decode the COMPLETE mb_type than. For values
of '0' in Intra-frames and values of '5' in P-Frames and '23' in
B-Frames you produce your error message. 



I went through the section that u told me. But my doubts were,
i dont understand what 0_0_0 signify in name of MB type. 

The 1. number in x_x_x  corresponds to column 5 of table 7-11

The 2. number....                                       column  6

The 3. number                                             column 7

Search for the label-text of these table-columns to get their exact
meaning

 

Also in table 7.13 mb_types for P slices, what do we mean by inferred
type.

Inferred means deduced. I simply says: if a macroblock does not appeare
in the bitstream (because it is skipped due to 'mb_skip_run' it
automatically has the type P_Skip and is 16x16 ....


Also tell me can we idetify the prediction mode from mb_type itself? 
Yes, every possible mode is part of the tables! Somewere in 7.4.5 you
find the note that you have to add the I-Table at the bottom of the P
and B tables, to signal Intra MB's in P and B-frames.  

 


thanks in advance,
mahesh.

On 8/7/07, List, Peter <Peter.List at t-systems.com> wrote: 

Dear Mahesh,

if you are talking about a DECODER intra 4x4 is a must, if you want to
be standard conform in all cases (for any profile). 

If you are talking about  ENCODERS you don't need to implement intra-4x4
but only use intra-16x16 (resulting in very poor intra performance).

 

I don't understand what you mean with:

But we want to decode any standard bitstream that is as per standard but
return the error code accordingly . 

About mb_type read in  "Recommendation H.264" (ISO/IEC 14496-10)
paragraph 7.4.5

 

Peter

 

________________________________

Von: mahesh k [mailto:maheswarreddy.k at gmail.com] 
Gesendet: Dienstag, 7. August 2007 11:22
An: Mailing list for x264 developers
Betreff: Re: [x264-devel] Regarding disabling 4x4 in JM code

 

thanks for ur reply. Plz tell me whether intra 4x4 is must in base line
profile or it is an optional.
 Can't we run the baseline profile decoder without 4x4 as per standard?
I need this because at present we have not implemented this 4x4 mode But
we want to decode any standard bitstream that is as per standard but
return the error code accordingly . 
Also I am confused with the syntax element mb_type. 
What values does mb_type should have if i need to check whether this is
an 4x4 or 16x16.
Also plz tell me in clear about this mb_type and ma_mde.
If possible refer some good document on this. 

Thanks in advance.

On 8/7/07, List, Peter <Peter.List at t-systems.com> wrote:


> mahesh k wrote:
> > I want a baseline ecoded bit stream in which intra4x4 predition mode
> > should not be present.
>
> Note (but you probably already know it): of course intra4x4 is part of

> baseline.

Also note that intra4x4 is NOT some fancy add on for intra-coding like
some people think 4x4 motion estimation is.
Intra4x4 is the basic intra coding mode! It is usually used for the
majority of intra-macroblocks. Intra-16x16 is only used for very uniform

macroblocks like blocks from a blue sky or something like that.
Regards, Peter
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