[PATCH] Document null muxer.

[Stefano Sabatini]

---
 doc/muxers.texi |   22 ++++++++++++++++++++++
 1 files changed, 22 insertions(+), 0 deletions(-)

diff --git a/doc/muxers.texi b/doc/muxers.texi
index d98abef..d661c96 100644
--- a/doc/muxers.texi
+++ b/doc/muxers.texi
@@ -109,4 +109,26 @@ ffmpeg -i file.mpg -acodec copy -vcodec copy \
      -y out.ts
 @end example
 
+ at section null
+
+Null muxer.
+
+This muxer does not generate any output file, it is mainly useful for
+testing or benchmarking purposes.
+
+For example to benchmark decoding with @file{ffmpeg} you can use the
+command:
+ at example
+ffmpeg -benchmark -i INPUT -f null out.null
+ at end example
+
+Note that the above command does not read or write the @file{out.null}
+file, but specifying the output file is required by the @file{ffmpeg}
+syntax.
+
+Alternatively you can write the command as:
+ at example
+ffmpeg -benchmark -i INPUT -f null -
+ at end example
+
 @c man end MUXERS
-- 
1.7.2.3


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