[FFmpeg-trac] #2852(avcodec:new): dcadec internal default downmix is not normalised and reduces stereo separation by cross mixing L* and R*.
FFmpeg
trac at avcodec.org
Sun Aug 11 12:30:53 CEST 2013
#2852: dcadec internal default downmix is not normalised and reduces stereo
separation by cross mixing L* and R*.
-------------------------------------+-------------------------------------
Reporter: AndyF | Type: defect
Status: new | Priority: normal
Component: avcodec | Version: git-
Keywords: dts dca | master
downmix | Blocked By:
Blocking: | Reproduced by developer: 0
Analyzed by developer: 0 |
-------------------------------------+-------------------------------------
Summary of the bug: When a dts 5.1 channel is downmixed to stereo with
-request_channels the results are faulty: not normalised and the L* and
R* channels are cross mixed albeit with reduced dB so some stereo effect
is still perceivable.
How to reproduce:
{{{
% ffmpeg -request_channels 2 -i 6ch.dts 2ch.wav
ffmpeg version - git
built on ... 10/08/13
}}}
Though this issue seems to exist for all dts samples I have - I don't have
many and totally failed to find a "normal" VOB channel check.
The channel check I used was core extracted from 7.1MA.
Looking at the code it seems that the default matrix in
libavcodec/dcadata.h looks
guilty assuming that dca_default_coeffs refers to dca_downmix_coeffs it
matches with the cross channel mixing that I can hear.
This also raises the question of why this matrix is used when I expected
studio dts material to have downmix meta data.
--
Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/2852>
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