[FFmpeg-devel] [PATCH] avfilter/f_ebur128: add dualmono measurement option

[Kyle Swanson]

> questions:
>
> - what happens if you resample the input (by prefixing ebur128 with
>   aformat=channel_layout=stereo)?
> - if I'm reading the blog correctly ("Note that In my discussions with
>   leading experts in the space, it has come to my attention that this
>   approach may not be sustainable. Many pros feel it is the responsibility
>   of the playback device and/or delivery system to apply the necessary
>   compensation.") this is not a standard behaviour at all. Do you confirm
>   this?

ffmpeg -nostats -i mono.wav -filter_complex
"aformat=channel_layouts=stereo,ebur128" -f null -
does not give the appropriate output. It looks like
`channel_layouts=stereo` is intelligent enough to
apply pan law gain to each channel before remapping, but this results
in the same inaccurate loudness
measurement.  A `dualmono=true` flag is convenient way to use the same
ffmpeg call to measure
loudness for all files, including multichannel files beyond stereo.

See also: a similar option is enabled by default in R128GAIN -
http://r128gain.sourceforge.net/

Thanks!
Kyle