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

[Nicolas George]

ffmpeg | branch: master | Nicolas George <nicolas.george at normalesup.org> | Tue Jan 24 12:42:20 2012 +0100| [9aaa70a845fe8eb26b3d2e264958b8586150d76b] | committer: Nicolas George

faq: document af_aconvert quirks using lavfi.

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=9aaa70a845fe8eb26b3d2e264958b8586150d76b
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 doc/faq.texi |   18 ++++++++++++++++++
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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
+lost.
+
+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
+aconvert=s16:stereo:packed
+ at end example
+
 @chapter Development
 
 @section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat?