[Libav-user] h264 getting dct coefficients in decoder

ULTRANj frozen-cs at yandex.ru
Fri May 27 20:35:54 CEST 2016

I want to implement LSB-steganography algorithm for h264-encoded video.

According to  this paper <http://www.cs.ox.ac.uk/andrew.ker/docs/ADK54B.pdf> 
, I need to modify the quantized coefficients in encoder, and translate
video (via vlc-media player).

The quality of the encoded video went bad and some steganography artifacts
occured in destination video player.

Now I want to extract hidden information, but I can't find a place in libav
codec, where decoder gets the DCT coefficients.

I checked the function *decode_cabac_residual_internal()* in *h264_cabac.c*
and dumped *block[]* of some coefficients there, but it differs from
coefficients , I dumped in encoder. 

Where is the place in decoder, where I can get dct coefficients, that i sent
from encoder?

Thanks, Nj

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