[FFmpeg-devel] [PATCH] faq: document af_aconvert quirks using lavfi.

Nicolas George nicolas.george at normalesup.org
Tue Jan 24 12:44:54 CET 2012

Signed-off-by: Nicolas George <nicolas.george at normalesup.org>
 doc/faq.texi |   18 ++++++++++++++++++
 1 files changed, 18 insertions(+), 0 deletions(-)

diff --git a/doc/faq.texi b/doc/faq.texi
index bd88da3..3fda98e 100644
--- a/doc/faq.texi
+++ b/doc/faq.texi
@@ -292,6 +292,24 @@ The solution is to apply the @option{-profile} option to the video stream only
 by using @url{http://ffmpeg.org/ffmpeg.html#Stream-specifiers-1, Stream specifiers}.
 Appending @code{:v} to it will do exactly that.
+ at section Using @option{-f lavfi}, audio becomes mono for no apparent reason.
+Use @option{-dumpgraph -} to find out exactly where the channel layout is
+Most likely, it is through @code{auto-inserted aconvert}. Try to understand
+why the converting filter was needed at that place.
+Just before the output is a lilely place, as @option{-f lavfi} currently
+only support packed S16.
+Then insert the correct @code{aconvert} explicitly in the filter graph,
+specifying the exact format.
+ at example
+ at end example
 @chapter Development
 @section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat?

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