From d339e03fc3b889fe60cc1dd00cdd18cb68aaa2ab Mon Sep 17 00:00:00 2001 From: Stefano Sabatini Date: Tue, 29 Oct 2013 21:50:09 +0100 Subject: doc/encoders: document the libfdk-aac wrapper Partially based on the https://trac.ffmpeg.org/wiki/AACEncodingGuide guide. --- doc/encoders.texi | 169 +++++++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 167 insertions(+), 2 deletions(-) (limited to 'doc/encoders.texi') diff --git a/doc/encoders.texi b/doc/encoders.texi index 7825b9a..840d55e 100644 --- a/doc/encoders.texi +++ b/doc/encoders.texi @@ -38,8 +38,8 @@ 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. -@c Comment this out until somebody writes the respective documentation. -@c See also @ref{libfaac}, @ref{libaacplus}, and @ref{libfdk-aac-enc}. +@c todo @ref{libfaac}, @ref{libaacplus} +See also @ref{libfdk-aac-enc,,the libfdk_aac section}. @subsection Options @@ -494,6 +494,171 @@ Selected by Encoder (default) @end table +@anchor{libfdk-aac-enc} +@section libfdk_aac + +libfdk-aac AAC (Advanced Audio Coding) encoder wrapper. + +The libfdk-aac library is based on the Fraunhofer FDK AAC code from +the Android project. + +Requires the presence of the libfdk-aac headers and library during +configuration. You need to explicitly configure the build with +@code{--enable-libfdk-aac}. The library is also incompatible with GPL, +so if you allow the use of GPL, you should configure with +@code{--enable-gpl --enable-nonfree --enable-libfdk-aac}. + +This encoder is considered to be of higher quality with respect to +both @ref{aacenc,,the native experimental FFmpeg AAC encoder} and +libfaac. + +For more information see the fdk-aac project at +@url{http://sourceforge.net/p/opencore-amr/fdk-aac/}. + +@subsection Options + +The following options are mapped on the shared FFmpeg codec options. + +@table @option +@item b +Set bit rate in bits/s. If the bitrate is not explicitly specified, it +is automatically set to a suitable value depending on the selected +profile. + +In case VBR mode is enabled the option is ignored. + +@item ar +Set audio sampling rate (in Hz). + +@item channels +Set the number of audio channels. + +@item flags +qscale +Enable fixed quality, VBR (Variable Bit Rate) mode. +Note that VBR is implicitely enabled when the @option{vbr} value is +positive. + +@item cutoff +Set cutoff frequency. If not specified (or explicitly set to 0) it +will use a value automatically computed by the library. Default value +is 0. + +@item profile +Set audio profile. + +The following profiles are recognized: +@table @samp +@item aac_low +Low Complexity AAC (LC) + +@item aac_he +High Efficiency AAC (HE-AAC) + +@item aac_he_v2 +High Efficiency AAC version 2 (HE-AACv2) + +@item aac_ld +Low Delay AAC (LD) + +@item aac_eld +Enhanced Low Delay AAC (ELD) +@end table + +If not specified it is set to @samp{aac_low}. +@end table + +The following are private options of the libfdk_aac encoder. + +@table @option +@item afterburner +Enable afterburner feature if set to 1, disabled if set to 0. This +improves the quality but also the required processing power. + +Default value is 1. + +@item eld_sbr +Enable SBR (Spectral Band Replication) for ELD if set to 1, disabled +if set to 0. + +Default value is 0. + +@item signaling +Set SBR/PS signaling style. + +It can assume one of the following values: +@table @samp +@item default +choose signaling implicitly (explicit hierarchical by default, +implicit if global header is disabled) + +@item implicit +implicit backwards compatible signaling + +@item explicit_sbr +explicit SBR, implicit PS signaling + +@item explicit_hierarchical +explicit hierarchical signaling +@end table + +Default value is @samp{default}. + +@item latm +Output LATM/LOAS encapsulated data if set to 1, disabled if set to 0. + +Default value is 0. + +@item header_period +Set StreamMuxConfig and PCE repetition period (in frames) for sending +in-band configuration buffers within LATM/LOAS transport layer. + +Must be a 16-bits non-negative integer. + +Default value is 0. + +@item vbr +Set VBR mode, from 1 to 5. 1 is lowest quality (though still pretty +good) and 5 is highest quality. A value of 0 will disable VBR mode, +and CBR (Constant Bit Rate) mode is enabled. + +Currently only the @samp{aac_low} profile supports VBR mode. + +VBR modes 1-5 correspond to roughly the following average bit rate: + +@table @samp +@item 1 +32 kbps/channel +@item 2 +40 kbps/channel +@item 3 +48-56 kbps/channel +@item 4 +64 kbps/channel +@item 5 +about 80-96 kbps/channel +@end table + +Default value is 0. +@end table + +@section Examples + +@itemize +@item +Use @command{ffmpeg} to convert an audio file to VBR AAC in an M4A (MP4) +container: +@example +ffmpeg -i input.wav -codec:a libfdk_aac -vbr 3 output.m4a +@end example + +@item +Use @command{ffmpeg} to convert an audio file to CBR 64k kbps AAC, using the +High-Efficiency AAC profile: +@example +ffmpeg -i input.wav -c:a libfdk_aac -profile:a aac_he -b:a 64k output.m4a +@end example +@end itemize + @anchor{libmp3lame} @section libmp3lame -- cgit v1.1