[FFmpeg-user] Erroneous volume level shifts using ffmpeg to convert AC3 in M2TS to WAV
lists at johnpilgrim.net
Sat Feb 28 23:59:33 CET 2015
I using ffmpeg to extract audio from non-commercial bluray m2ts video files, for subsequent loudness analysis in AudioLeak or Dolby Media Meter. The m2ts sometimes have AC3 audio and sometimes have linear PCM audio. I wish to output a WAV file. The command I am using is
ffmpeg -i foo.m2ts foo.wav
The volume levels of the WAV files are not accurate compared to the corresponding AC3 files.
Here's what I mean: If I extract the ac3 audio instead, using
ffmpeg -i foo.m2ts -acodec copy -f ac3 foo.ac3
and run both through Dolby Media Meter, the loudness and peak levels of the WAV are shifted up/or down compared to the corresponding AC3 file.
And this is happening with AC3 files with a DIALNORM metadata value of -31, which per the Dolby specs, should result in NO volume level change, as -31 is the reference point.
Does anyone have any insight into what's going on, or recommendations for a better invocation of ffmpeg?
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