Thank you Andy! ffmpeg -drc_scale 0 -i foo.m2ts foo.wav worked perfectly and the loudness measurements of the AC3 and WAV extractions now match, as they should. To wit, http://johnpilgrimdesign.com/client/loudness/SCowR25LKFS/#lifeofsock Thanks again, John
On Feb 28, 2015, at 3:44 PM, Andy Furniss <[email protected]> wrote: > John Pilgrim wrote: >> 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? > > By default ac3dec will apply full DRC if there is any there it doesn't > use dialnorm by default. > > To get full range DRC wise do > > ffmpeg -drc_scale 0 -i foo.m2ts > > WRT dialnorm - I am not familiar with Dolby s/w, but I think it's > possible that some decoders would scale up to a target higher than -31 > depending on how they are set - so just because the stream is -31 I am > not sure that excludes the possibility that a decoder will adjust - > target level is a decoder setting. > _______________________________________________ _______________________________________________ ffmpeg-user mailing list [email protected] http://ffmpeg.org/mailman/listinfo/ffmpeg-user
