[FFmpeg-devel] DCT Coefficients Debugging

Michael Niedermayer michaelni
Mon Jun 11 10:20:23 CEST 2007


On Mon, Jun 11, 2007 at 08:35:47AM +0200, Benjamin Bohlmann wrote:
> Hello All,
> I'm not sure if this question belongs here or on ffmpeg-users. If I  
> posted to the wrong list, please give me a hint and I'll repost it to  
> the correct list.
> I'm trying to extract the DCT coefficent information from a mpeg2  
> video frame that was decoded with libavcodec. I understand that when  
> I turn FF_DEBUG_DCT_COEFF on, that this information is stored in  
> AVFrame->dct_coeff. I read through this list and the source code, but  
> couldn't find any information on how the data inside the dct_coeff  
> field is organized. The only thing that I found out by reading the  
> source, is that for each macroblock 6x64 dct coefficients are written  
> into this field. Can I interpret this as four 8x8 blocks of Luminance  
> (Y) coefficients followed by one 8x8 block of Cb and one 8x8 block of  
> Cr? Is the order of the Y-Blocks "top-left, top-right, bottom-left,  
> bottom-right"? 

yes sounds correct

> If this is true, where can I find the DCT information  
> for the remaining Chrominance blocks for 4:2:2 or 4:4:4 coded  
> macroblocks?

probably not in any public place ...
patch welcome ...

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Opposition brings concord. Out of discord comes the fairest harmony.
-- Heraclitus
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