lavfi: add aecho filter

Signed-off-by: Paul B Mahol <onemda@gmail.com>

1 files changed, 60 insertions, 0 deletions

diff --git a/doc/filters.texi b/doc/filters.texi
index 33436ad267..92f86124cd 100644
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -347,6 +347,66 @@ aconvert=u8:auto
 @end example
 @end itemize
 
+@section aecho
+
+Apply echoing to the input audio.
+
+Echoes are reflected sound and can occur naturally amongst mountains
+(and sometimes large buildings) when talking or shouting; digital echo
+effects emulate this behaviour and are often used to help fill out the
+sound of a single instrument or vocal. The time difference between the
+original signal and the reflection is the @code{delay}, and the
+loudness of the reflected signal is the @code{decay}.
+Multiple echoes can have different delays and decays.
+
+A description of the accepted parameters follows.
+
+@table @option
+@item in_gain
+Set input gain of reflected signal. Default is @code{0.6}.
+
+@item out_gain
+Set output gain of reflected signal. Default is @code{0.3}.
+
+@item delays
+Set list of time intervals in milliseconds between original signal and reflections
+separated by '|'. Allowed range for each @code{delay} is @code{(0 - 90000.0]}.
+Default is @code{1000}.
+
+@item decays
+Set list of loudnesses of reflected signals separated by '|'.
+Allowed range for each @code{decay} is @code{(0 - 1.0]}.
+Default is @code{0.5}.
+@end table
+
+@subsection Examples
+
+@itemize
+@item
+Make it sound as if there are twice as many instruments as are actually playing:
+@example
+aecho=0.8:0.88:60:0.4
+@end example
+
+@item
+If delay is very short, then it sound like a (metallic) robot playing music:
+@example
+aecho=0.8:0.88:6:0.4
+@end example
+
+@item
+A longer delay will sound like an open air concert in the mountains:
+@example
+aecho=0.8:0.9:1000:0.3
+@end example
+
+@item
+Same as above but with one more mountain:
+@example
+aecho=0.8:0.9:1000|1800:0.3|0.25
+@end example
+@end itemize
+
 @section afade
 
 Apply fade-in/out effect to input audio.