[FFmpeg-devel] [PATCH v3] doc/filters: Add double-pass example for loudnorm

[Marvin Scholz]

---
Changes to v2:

- Removed -map option to prevent filter to affect all audio channels
  in the first pass example

 doc/filters.texi | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/doc/filters.texi b/doc/filters.texi
index 32c95b591c..f082d55d32 100644
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -3659,6 +3659,29 @@ Set print format for stats. Options are summary, json, or none.
 Default value is none.
 @end table
 
+ at subsection Examples
+
+For double pass processing you need to first run the filter with
+ at code{print_format} set to either @code{json} or @code{summary}, then read
+the values in the output and pass it to the next run of the filter:
+
+ at example
+$ ffmpeg -i input -af loudnorm=I=-23:TP=-1:print_format=summary -f null -
+
+[...]
+Input Integrated:     -9.0 LUFS
+Input True Peak:      +1.5 dBTP
+Input LRA:             9.4 LU
+Input Threshold:     -19.5 LUFS
+ at end example
+
+Then pass the input measurements to the next run that produces the result:
+
+ at example
+ffmpeg -i input -af loudnorm=I=-23:TP=-1:measured_I=-9.0:measured_TP=1.5:measured_LRA=9.4:measured_thresh=-19.5:print_format=summary output
+ at end example
+
+
 @section lowpass
 
 Apply a low-pass filter with 3dB point frequency.
-- 
2.17.0 (Apple Git-106)