[FFmpeg-devel] [PATCH 2/3] doc/encoders: add doc for AAC encoder

Timothy Gu timothygu99 at gmail.com
Mon Sep 9 02:02:05 CEST 2013

Thanks-to: Kostya Shishkov <kostya.shishkov at gmail.com>
Signed-off-by: Timothy Gu <timothygu99 at gmail.com>
 doc/encoders.texi | 91 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 91 insertions(+)

diff --git a/doc/encoders.texi b/doc/encoders.texi
index f85e9c6..3ef8f6b 100644
--- a/doc/encoders.texi
+++ b/doc/encoders.texi
@@ -25,6 +25,96 @@ enabled encoders.
 A description of some of the currently available audio encoders
+ at anchor{aacenc}
+ at section aac
+Advanced Audio Coding (AAC) encoder.
+This encoder is an experimental FFmpeg-native AAC encoder. Currently only the
+low complexity (AAC-LC) profile is supported. To use this encoder, you must set
+ at option{strict} option to @samp{experimental} or lower.
+We have done our best to keep this encoder bug-free; however, as this encoder
+is experimental, unexpected behavior may exist from time to time. For a more
+stable AAC encoder, see @ref{libvo-aacenc}. However, be warned that it has a
+worse quality reported by some users.
+ at c Comment this out until somebody writes the respective documentation.
+ at c See also @ref{libfaac}, @ref{libaacplus}, and @ref{libfdk-aac-enc}.
+ at subsection Options
+ at table @option
+ at item b
+Set bit rate in bits/s. Setting this automatically activates constant bit rate
+(CBR) mode.
+ at item q
+Set quality for variable bit rate (VBR) mode. This option is valid only using
+the @command{ffmpeg} command-line tool. For library interface users, use
+ at option{global_quality}.
+ at item stereo_mode
+Set stereo encoding mode. Possible values:
+ at table @samp
+ at item auto
+Automatically selected by the encoder.
+ at item ms_off
+Disable middle/side encoding.
+ at item ms_force
+Force middle/side encoding.
+ at end table
+ at item aac_coder
+Set AAC encoder coding method. Possible values:
+ at table @samp
+ at item faac
+FAAC-inspired method.
+This method is a simplified reimplementation of the method used in FAAC, which
+sets thresholds proportional to the band energies, and then decreases all the
+thresholds with quantizer steps to find the appropriate quantization with
+distortion below threshold band by band.
+The quality of this method is comparable to the two loop searching method
+descibed below, but somewhat a little better and slower.
+ at item anmr
+Average noise to mask ratio (ANMR) trellis-based solution.
+This has a theoretic best quality out of all the coding methods, but at the
+cost of the slowest speed.
+ at item twoloop
+Two loop searching (TLS) method.
+This method first sets quantizers depending on band thresholds and then tries
+to find an optimal combination by adding or subtracting a specific value from
+all quantizers and adjusting some individual quantizer a little.
+This method produces similar quality with the FAAC method and is the default.
+ at item fast
+Constant quantizer method.
+This method sets a constant quantizer for all bands. This is the fastest of all
+the methods, yet produces the worst quality.
+ at end table
+ at end table
+ at subsection Tips and Tricks
+According to some reports
+(e.g. @url{http://d.hatena.ne.jp/kamedo2/20120729/1343545890}), setting the
+ at option{cutoff} option to 15000 Hz greatly improves the quality of the output
+quality. As a result, we encourage you to do the same.
 @section ac3 and ac3_fixed
 AC-3 audio encoders.
@@ -553,6 +643,7 @@ Set MPEG audio original flag when set to 1. The default value is 0
 @end table
+ at anchor{libvo-aacenc}
 @section libvo-aacenc
 VisualOn AAC encoder.

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