lavfi/ebur128: add sample and true peak metering.

Metadata injection and logging. Not yet present visually.
Signed-off-by: Jean First <jeanfirst@gmail.com>

doc/filters.texi

@@ -9322,6 +9322,27 @@ verbose logging level
 
 By default, the logging level is set to @var{info}. If the @option{video} or
 the @option{metadata} options are set, it switches to @var{verbose}.
+
+@item peak
+Set peak mode(s).
+
+Available modes can be cumulated (the option is a @code{flag} type). Possible
+values are:
+@table @samp
+@item none
+Disable any peak mode (default).
+@item sample
+Enable sample-peak mode.
+
+Simple peak mode looking for the higher sample value.
+@item true
+Enable true-peak mode.
+
+If enabled, the peak lookup is done on an over-sampled version of the input
+stream for better peak accuracy. This mode requires a build with
+@code{libswresample}.
+@end table
+
 @end table
 
 @subsection Examples

libavfilter/Makefile

@@ -22,6 +22,8 @@ FFLIBS-$(CONFIG_SCALE_FILTER)                += swscale
 FFLIBS-$(CONFIG_SHOWSPECTRUM_FILTER)         += avcodec
 FFLIBS-$(CONFIG_SMARTBLUR_FILTER)            += swscale
 FFLIBS-$(CONFIG_SUBTITLES_FILTER)            += avformat avcodec
+EBUR128LIBS-$(CONFIG_SWRESAMPLE)              = swresample
+FFLIBS-$(CONFIG_EBUR128_FILTER)              += $(EBUR128LIBS-yes)
 
 HEADERS = asrc_abuffer.h                                                \
           avcodec.h                                                     \