[FFmpeg-devel] [PATCH] doc/encoders: add libfaac encoder documentation

[Timothy Gu]

On Oct 30, 2013 6:26 AM, "Stefano Sabatini" <stefasab at gmail.com> wrote:
>
> ---
>  doc/encoders.texi | 119
+++++++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 117 insertions(+), 2 deletions(-)
>
> diff --git a/doc/encoders.texi b/doc/encoders.texi
> index 54157f0..a9d518a 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.
>
> - at c todo @ref{libfaac}, @ref{libaacplus}
> -See also @ref{libfdk-aac-enc,,the libfdk_aac section}.
> + at c todo @ref{libaacplus}
> +See also @ref{libfdk-aac-enc,,libfdk_aac} and @ref{libfaac}.
>
>  @subsection Options
>
> @@ -494,6 +494,121 @@ Selected by Encoder (default)
>
>  @end table
>
> + at anchor{libfaac}
> + at section libfaac
> +
> +libfaac 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 libfaac headers and library during
> +configuration. You need to explicitly configure the build with
> + at code{--enable-libfaac --enable-nonfree}.
> +
> +This encoder is considered to be of higher quality with respect to the
> + at ref{aacenc,,the native experimental FFmpeg AAC encoder}.

...with respect to aac and libvo-aacenc...but somehow worse compared to
libfdk-aac.

> +
> +For more information see the libfaac project at
> + at url{http://sourceforge.net/projects/faac/}.

The real URL is http://www.audiocoding.com/faac.html

> +
> + at subsection Options
> +
> +The following shared FFmpeg codec options are recognized.
> +
> +The following options are supported by the libfaac wrapper. The
> + at command{faac}-equivalent of the options are listed in parentheses.
> +
> + at table @option
> + at item b (@emph{-b})
> +Set bit rate in bits/s for ABR (Average Bit Rate) mode. If the bitrate

"bit rate" with space in between for consistency.

> +is not explicitly specified, it is automatically set to a suitable
> +value depending on the selected profile. @command{faac} bitrate is
> +expressed in kilobits/s.

@command{faac} @option{-b} option is expressed...

> +
> +Note that libfaac does not support CBR (Constant Bit Rate) but only
> +ABR (Average Bit Rate).
> +
> +In case VBR mode is enabled this option is ignored.

In case of

> +
> + at item ar (@emph{-R})
> +Set audio sampling rate (in Hz).
> +
> + at item ac (@emph{-c})
> +Set the number of audio channels.

Not sure if these two are necessary.

> +
> + at item cutoff (@emph{-C})
> +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.
> +
> + at item profile
> +Set audio profile.
> +
> +The following profiles are recognized:
> + at table @samp
> + at item aac_main
> +Main AAC (Main)
> +
> + at item aac_low
> +Low Complexity AAC (LC)
> +

> + at item aac_he
> +High Efficiency AAC (HE-AAC)

Faac doesn't support aac_he.

> +
> + at item aac_ssr
> +Scalable Sample Rate (SSR)
> +
> + at item aac_ltp
> +Long Term Prediction (LTP)
> + at end table
> +
> +If not specified it is set to @samp{aac_low}.
> +
> + at item flags +qscale
> +Set constant quality VBR (Variable Bit Rate) mode.
> +
> + at item global_quality
> +Set quality in VBR mode as an integer.
> +
> +Only relevant when VBR mode is enabled with @code{flags +qscale}.
> + at option{global_quality} is expressed in Lagrange units. To get the
> +corresponding QP value you need to divide by the @code{FF_QP2LAMBDA}
> +constant. The higher the value the higher the quality.
> +
> +Default value is 0.
> +
> + at item q (@emph{-q})
> +Enable VBR mode, and set constant quality value as an integer.
> +
> +This option is valid only using the @command{ffmpeg} command-line
> +tool. The value is expressed in QP units, the higher the value the
> +higher the quality. A reasonable range for the option value is
> +[10-500].

The valid range for...

> +
> +Default value is 0.
> +
> +For library interface users, use @option{global_quality}.
> + at end table
> +
> + at subsection Examples
> +
> + at itemize
> + at item
> +Use @command{ffmpeg} to convert an audio file to ABR 128kbps AAC in an
M4A (MP4)

Nnnnnit: 128 kbps with space

> +container:
> + at example
> +ffmpeg -i input.wav -codec:a libfaac -b:a 128k -output.m4a
> + at end example
> +

> + at item
> +Use @command{ffmpeg} to convert an audio file to VBR AAC, using the
> +High-Efficiency AAC profile:
> + at example
> +ffmpeg -i input.wav -c:a libfaac -profile:a aac_he -q:a 100 output.m4a
> + at end example
> + at end itemize

Again, faac doesn't support HE.

> +
>  @anchor{libfdk-aac-enc}
>  @section libfdk_aac
>
> --
> 1.8.1.2

Timothy