[FFmpeg-trac] #9352(avfilter:new): loudnorm filter goofs loudness measurements in some cases
FFmpeg
trac at avcodec.org
Fri Jul 30 02:10:23 EEST 2021
#9352: loudnorm filter goofs loudness measurements in some cases
-------------------------------------+-------------------------------------
Reporter: Gregory | Type: defect
Beauregard |
Status: new | Priority: normal
Component: avfilter | Version:
| unspecified
Keywords: | Blocked By:
Blocking: | Reproduced by developer: 0
Analyzed by developer: 0 |
-------------------------------------+-------------------------------------
Summary of the bug: The loudnorm filter can badly goof the integrated
loudness in certain situations (e.g. particular noise after a resample)
resulting in significant distortion if attempting to use it.
Using the attached file `loudnorm_samp.mkv` (4.7 MB), 48 kHz DTS-HD,
analyze the loudness with loudnorm to get integrated loudness ~-21:
`"input_i" : "-21.57"`:
{{{
ffmpeg -i loudnorm_samp.mkv -af
aresample=ocl=stereo,loudnorm=print_format=json -f null -
}}}
However, when we reanalyze it by giving the resampler a dither and
specifying 48 kHz, the loudnorm filter goofs the integrated loudness with
0.13: "input_i" : "0.13"`:
{{{
ffmpeg -i loudnorm_samp.mkv -af
aresample=ocl=stereo:dither_method=shibata:osr=48000,loudnorm=print_format=json
-f null -
}}}
This results in really wrong re-normalization resulting in significant
distortion. If we run `ebur128` to analyze the loudness instead of
`loudnorm` in the situation where it goofs, `ebur128` outputs an expected
-22.2 integrated loudness, and doesn't change between the two situations
above:
{{{
ffmpeg -i loudnorm_samp.mkv -af
aresample=ocl=stereo:dither_method=shibata:osr=48000,ebur128 -f null -
}}}
So there's some odd sensitivity in the `loudnorm` filter that's messing it
up where `ebur128` is still ok.
--
Ticket URL: <https://trac.ffmpeg.org/ticket/9352>
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