libavfilter/af_hdcd.c: Collect HDCD stats and report

The new HDCD filter really does nothing to show that it is working or
that HDCD control information was even detected in the stream. This
patch collects information about the decode, like which features were
used, and reports it to the user at the end.

Also,
* Fixes low-level gain adjustment
* Updates the documentation

Signed-off-by: Burt P <pburt0@gmail.com>
Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

1 files changed, 17 insertions, 2 deletions

diff --git a/doc/filters.texi b/doc/filters.texi
index 3cf3d7ce89..a8c2c8799d 100644
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -8427,8 +8427,23 @@ ffplay input.mkv -vf "movie=clut.png, [in] haldclut"
 
 @section hdcd
 
-Decodes high definition audio cd data. 16-Bit PCM stream containing hdcd flags
-is converted to 20-bit PCM stream.
+Decodes High Definition Compatible Digital (HDCD) data. A 16-bit PCM stream with
+embedded HDCD codes is expanded into a 20-bit PCM stream.
+
+The filter supports the Peak Extend and Low-level Gain Adjustment features
+of HDCD, and detects the Transient Filter flag.
+
+@example
+ffmpeg -i HDCD16.flac -af hdcd OUT24.flac
+@end example
+
+When using the filter with wav, note the default encoding for wav is 16-bit,
+so the resulting 20-bit stream will be truncated back to 16-bit. Use something
+like @command{-acodec pcm_s24le} after the filter to get 24-bit PCM output.
+@example
+ffmpeg -i HDCD16.wav -af hdcd OUT16.wav
+ffmpeg -i HDCD16.wav -af hdcd -acodec pcm_s24le OUT24.wav
+@end example
 
 @section hflip