doc/encoders.texi - third_party/ffmpeg - Git at Google

 @chapter Encoders
 @c man begin ENCODERS

 Encoders are configured elements in FFmpeg which allow the encoding of
 multimedia streams.

 When you configure your FFmpeg build, all the supported native encoders
 are enabled by default. Encoders requiring an external library must be enabled
 manually via the corresponding @code{--enable-lib} option. You can list all
 available encoders using the configure option @code{--list-encoders}.

 You can disable all the encoders with the configure option
 @code{--disable-encoders} and selectively enable / disable single encoders
 with the options @code{--enable-encoder=@var{ENCODER}} /
 @code{--disable-encoder=@var{ENCODER}}.

 The option @code{-codecs} of the ff* tools will display the list of
 enabled encoders.

 @c man end ENCODERS

 @chapter Audio Encoders
 @c man begin AUDIO ENCODERS

 A description of some of the currently available audio encoders
 follows.

 @section ac3 and ac3_fixed

 AC-3 audio encoders.

 These encoders implement part of ATSC A/52:2010 and ETSI TS 102 366, as well as
 the undocumented RealAudio 3 (a.k.a. dnet).

 The @var{ac3} encoder uses floating-point math, while the @var{ac3_fixed}
 encoder only uses fixed-point integer math. This does not mean that one is
 always faster, just that one or the other may be better suited to a
 particular system. The floating-point encoder will generally produce better
 quality audio for a given bitrate. The @var{ac3_fixed} encoder is not the
 default codec for any of the output formats, so it must be specified explicitly
 using the option @code{-acodec ac3_fixed} in order to use it.

 @subsection AC-3 Metadata

 The AC-3 metadata options are used to set parameters that describe the audio,
 but in most cases do not affect the audio encoding itself. Some of the options
 do directly affect or influence the decoding and playback of the resulting
 bitstream, while others are just for informational purposes. A few of the
 options will add bits to the output stream that could otherwise be used for
 audio data, and will thus affect the quality of the output. Those will be
 indicated accordingly with a note in the option list below.

 These parameters are described in detail in several publicly-available
 documents.
 @itemize
 @item @uref{http://www.atsc.org/cms/standards/a_52-2010.pdf,A/52:2010 - Digital Audio Compression (AC-3) (E-AC-3) Standard}
 @item @uref{http://www.atsc.org/cms/standards/a_54a_with_corr_1.pdf,A/54 - Guide to the Use of the ATSC Digital Television Standard}
 @item @uref{http://www.dolby.com/uploadedFiles/zz-_Shared_Assets/English_PDFs/Professional/18_Metadata.Guide.pdf,Dolby Metadata Guide}
 @item @uref{http://www.dolby.com/uploadedFiles/zz-_Shared_Assets/English_PDFs/Professional/46_DDEncodingGuidelines.pdf,Dolby Digital Professional Encoding Guidelines}
 @end itemize

 @subsubsection Metadata Control Options

 @table @option

 @item -per_frame_metadata @var{boolean}
 Allow Per-Frame Metadata. Specifies if the encoder should check for changing
 metadata for each frame.
 @table @option
 @item 0
 The metadata values set at initialization will be used for every frame in the
 stream. (default)
 @item 1
 Metadata values can be changed before encoding each frame.
 @end table

 @end table

 @subsubsection Downmix Levels

 @table @option

 @item -center_mixlev @var{level}
 Center Mix Level. The amount of gain the decoder should apply to the center
 channel when downmixing to stereo. This field will only be written to the
 bitstream if a center channel is present. The value is specified as a scale
 factor. There are 3 valid values:
 @table @option
 @item 0.707
 Apply -3dB gain
 @item 0.595
 Apply -4.5dB gain (default)
 @item 0.500
 Apply -6dB gain
 @end table

 @item -surround_mixlev @var{level}
 Surround Mix Level. The amount of gain the decoder should apply to the surround
 channel(s) when downmixing to stereo. This field will only be written to the
 bitstream if one or more surround channels are present. The value is specified
 as a scale factor.  There are 3 valid values:
 @table @option
 @item 0.707
 Apply -3dB gain
 @item 0.500
 Apply -6dB gain (default)
 @item 0.000
 Silence Surround Channel(s)
 @end table

 @end table

 @subsubsection Audio Production Information
 Audio Production Information is optional information describing the mixing
 environment.  Either none or both of the fields are written to the bitstream.

 @table @option

 @item -mixing_level @var{number}
 Mixing Level. Specifies peak sound pressure level (SPL) in the production
 environment when the mix was mastered. Valid values are 80 to 111, or -1 for
 unknown or not indicated. The default value is -1, but that value cannot be
 used if the Audio Production Information is written to the bitstream. Therefore,
 if the @code{room_type} option is not the default value, the @code{mixing_level}
 option must not be -1.

 @item -room_type @var{type}
 Room Type. Describes the equalization used during the final mixing session at
 the studio or on the dubbing stage. A large room is a dubbing stage with the
 industry standard X-curve equalization; a small room has flat equalization.
 This field will not be written to the bitstream if both the @code{mixing_level}
 option and the @code{room_type} option have the default values.
 @table @option
 @item 0
 @itemx notindicated
 Not Indicated (default)
 @item 1
 @itemx large
 Large Room
 @item 2
 @itemx small
 Small Room
 @end table

 @end table

 @subsubsection Other Metadata Options

 @table @option

 @item -copyright @var{boolean}
 Copyright Indicator. Specifies whether a copyright exists for this audio.
 @table @option
 @item 0
 @itemx off
 No Copyright Exists (default)
 @item 1
 @itemx on
 Copyright Exists
 @end table

 @item -dialnorm @var{value}
 Dialogue Normalization. Indicates how far the average dialogue level of the
 program is below digital 100% full scale (0 dBFS). This parameter determines a
 level shift during audio reproduction that sets the average volume of the
 dialogue to a preset level. The goal is to match volume level between program
 sources. A value of -31dB will result in no volume level change, relative to
 the source volume, during audio reproduction. Valid values are whole numbers in
 the range -31 to -1, with -31 being the default.

 @item -dsur_mode @var{mode}
 Dolby Surround Mode. Specifies whether the stereo signal uses Dolby Surround
 (Pro Logic). This field will only be written to the bitstream if the audio
 stream is stereo. Using this option does @b{NOT} mean the encoder will actually
 apply Dolby Surround processing.
 @table @option
 @item 0
 @itemx notindicated
 Not Indicated (default)
 @item 1
 @itemx off
 Not Dolby Surround Encoded
 @item 2
 @itemx on
 Dolby Surround Encoded
 @end table

 @item -original @var{boolean}
 Original Bit Stream Indicator. Specifies whether this audio is from the
 original source and not a copy.
 @table @option
 @item 0
 @itemx off
 Not Original Source
 @item 1
 @itemx on
 Original Source (default)
 @end table

 @end table

 @subsection Extended Bitstream Information
 The extended bitstream options are part of the Alternate Bit Stream Syntax as
 specified in Annex D of the A/52:2010 standard. It is grouped into 2 parts.
 If any one parameter in a group is specified, all values in that group will be
 written to the bitstream.  Default values are used for those that are written
 but have not been specified.  If the mixing levels are written, the decoder
 will use these values instead of the ones specified in the @code{center_mixlev}
 and @code{surround_mixlev} options if it supports the Alternate Bit Stream
 Syntax.

 @subsubsection Extended Bitstream Information - Part 1

 @table @option

 @item -dmix_mode @var{mode}
 Preferred Stereo Downmix Mode. Allows the user to select either Lt/Rt
 (Dolby Surround) or Lo/Ro (normal stereo) as the preferred stereo downmix mode.
 @table @option
 @item 0
 @itemx notindicated
 Not Indicated (default)
 @item 1
 @itemx ltrt
 Lt/Rt Downmix Preferred
 @item 2
 @itemx loro
 Lo/Ro Downmix Preferred
 @end table

 @item -ltrt_cmixlev @var{level}
 Lt/Rt Center Mix Level. The amount of gain the decoder should apply to the
 center channel when downmixing to stereo in Lt/Rt mode.
 @table @option
 @item 1.414
 Apply +3dB gain
 @item 1.189
 Apply +1.5dB gain
 @item 1.000
 Apply 0dB gain
 @item 0.841
 Apply -1.5dB gain
 @item 0.707
 Apply -3.0dB gain
 @item 0.595
 Apply -4.5dB gain (default)
 @item 0.500
 Apply -6.0dB gain
 @item 0.000
 Silence Center Channel
 @end table

 @item -ltrt_surmixlev @var{level}
 Lt/Rt Surround Mix Level. The amount of gain the decoder should apply to the
 surround channel(s) when downmixing to stereo in Lt/Rt mode.
 @table @option
 @item 0.841
 Apply -1.5dB gain
 @item 0.707
 Apply -3.0dB gain
 @item 0.595
 Apply -4.5dB gain
 @item 0.500
 Apply -6.0dB gain (default)
 @item 0.000
 Silence Surround Channel(s)
 @end table

 @item -loro_cmixlev @var{level}
 Lo/Ro Center Mix Level. The amount of gain the decoder should apply to the
 center channel when downmixing to stereo in Lo/Ro mode.
 @table @option
 @item 1.414
 Apply +3dB gain
 @item 1.189
 Apply +1.5dB gain
 @item 1.000
 Apply 0dB gain
 @item 0.841
 Apply -1.5dB gain
 @item 0.707
 Apply -3.0dB gain
 @item 0.595
 Apply -4.5dB gain (default)
 @item 0.500
 Apply -6.0dB gain
 @item 0.000
 Silence Center Channel
 @end table

 @item -loro_surmixlev @var{level}
 Lo/Ro Surround Mix Level. The amount of gain the decoder should apply to the
 surround channel(s) when downmixing to stereo in Lo/Ro mode.
 @table @option
 @item 0.841
 Apply -1.5dB gain
 @item 0.707
 Apply -3.0dB gain
 @item 0.595
 Apply -4.5dB gain
 @item 0.500
 Apply -6.0dB gain (default)
 @item 0.000
 Silence Surround Channel(s)
 @end table

 @end table

 @subsubsection Extended Bitstream Information - Part 2

 @table @option

 @item -dsurex_mode @var{mode}
 Dolby Surround EX Mode. Indicates whether the stream uses Dolby Surround EX
 (7.1 matrixed to 5.1). Using this option does @b{NOT} mean the encoder will actually
 apply Dolby Surround EX processing.
 @table @option
 @item 0
 @itemx notindicated
 Not Indicated (default)
 @item 1
 @itemx on
 Dolby Surround EX Off
 @item 2
 @itemx off
 Dolby Surround EX On
 @end table

 @item -dheadphone_mode @var{mode}
 Dolby Headphone Mode. Indicates whether the stream uses Dolby Headphone
 encoding (multi-channel matrixed to 2.0 for use with headphones). Using this
 option does @b{NOT} mean the encoder will actually apply Dolby Headphone
 processing.
 @table @option
 @item 0
 @itemx notindicated
 Not Indicated (default)
 @item 1
 @itemx on
 Dolby Headphone Off
 @item 2
 @itemx off
 Dolby Headphone On
 @end table

 @item -ad_conv_type @var{type}
 A/D Converter Type. Indicates whether the audio has passed through HDCD A/D
 conversion.
 @table @option
 @item 0
 @itemx standard
 Standard A/D Converter (default)
 @item 1
 @itemx hdcd
 HDCD A/D Converter
 @end table

 @end table

 @subsection Other AC-3 Encoding Options

 @table @option

 @item -stereo_rematrixing @var{boolean}
 Stereo Rematrixing. Enables/Disables use of rematrixing for stereo input. This
 is an optional AC-3 feature that increases quality by selectively encoding
 the left/right channels as mid/side. This option is enabled by default, and it
 is highly recommended that it be left as enabled except for testing purposes.

 @end table

 @subsection Floating-Point-Only AC-3 Encoding Options

 These options are only valid for the floating-point encoder and do not exist
 for the fixed-point encoder due to the corresponding features not being
 implemented in fixed-point.

 @table @option

 @item -channel_coupling @var{boolean}
 Enables/Disables use of channel coupling, which is an optional AC-3 feature
 that increases quality by combining high frequency information from multiple
 channels into a single channel. The per-channel high frequency information is
 sent with less accuracy in both the frequency and time domains. This allows
 more bits to be used for lower frequencies while preserving enough information
 to reconstruct the high frequencies. This option is enabled by default for the
 floating-point encoder and should generally be left as enabled except for
 testing purposes or to increase encoding speed.
 @table @option
 @item -1
 @itemx auto
 Selected by Encoder (default)
 @item 0
 @itemx off
 Disable Channel Coupling
 @item 1
 @itemx on
 Enable Channel Coupling
 @end table

 @item -cpl_start_band @var{number}
 Coupling Start Band. Sets the channel coupling start band, from 1 to 15. If a
 value higher than the bandwidth is used, it will be reduced to 1 less than the
 coupling end band. If @var{auto} is used, the start band will be determined by
 the encoder based on the bit rate, sample rate, and channel layout. This option
 has no effect if channel coupling is disabled.
 @table @option
 @item -1
 @itemx auto
 Selected by Encoder (default)
 @end table

 @end table

 @c man end AUDIO ENCODERS

 @chapter Video Encoders
 @c man begin VIDEO ENCODERS

 A description of some of the currently available video encoders
 follows.

 @section libvpx

 VP8 format supported through libvpx.

 Requires the presence of the libvpx headers and library during configuration.
 You need to explicitly configure the build with @code{--enable-libvpx}.

 @subsection Options

 Mapping from FFmpeg to libvpx options with conversion notes in parentheses.

 @table @option

 @item threads
 g_threads

 @item profile
 g_profile

 @item vb
 rc_target_bitrate

 @item g
 kf_max_dist

 @item keyint_min
 kf_min_dist

 @item qmin
 rc_min_quantizer

 @item qmax
 rc_max_quantizer

 @item bufsize, vb
 rc_buf_sz
 @code{(bufsize * 1000 / vb)}

 rc_buf_optimal_sz
 @code{(bufsize * 1000 / vb * 5 / 6)}

 @item rc_init_occupancy, vb
 rc_buf_initial_sz
 @code{(rc_init_occupancy * 1000 / vb)}

 @item rc_buffer_aggressivity
 rc_undershoot_pct

 @item skip_threshold
 rc_dropframe_thresh

 @item qcomp
 rc_2pass_vbr_bias_pct

 @item maxrate, vb
 rc_2pass_vbr_maxsection_pct
 @code{(maxrate * 100 / vb)}

 @item minrate, vb
 rc_2pass_vbr_minsection_pct
 @code{(minrate * 100 / vb)}

 @item minrate, maxrate, vb
 @code{VPX_CBR}
 @code{(minrate == maxrate == vb)}

 @item crf
 @code{VPX_CQ}, @code{VP8E_SET_CQ_LEVEL}

 @item quality
 @table @option
 @item @var{best}
 @code{VPX_DL_BEST_QUALITY}
 @item @var{good}
 @code{VPX_DL_GOOD_QUALITY}
 @item @var{realtime}
 @code{VPX_DL_REALTIME}
 @end table

 @item speed
 @code{VP8E_SET_CPUUSED}

 @item nr
 @code{VP8E_SET_NOISE_SENSITIVITY}

 @item mb_threshold
 @code{VP8E_SET_STATIC_THRESHOLD}

 @item slices
 @code{VP8E_SET_TOKEN_PARTITIONS}

 @item Alternate reference frame related
 @table @option
 @item vp8flags altref
 @code{VP8E_SET_ENABLEAUTOALTREF}
 @item @var{arnr_max_frames}
 @code{VP8E_SET_ARNR_MAXFRAMES}
 @item @var{arnr_type}
 @code{VP8E_SET_ARNR_TYPE}
 @item @var{arnr_strength}
 @code{VP8E_SET_ARNR_STRENGTH}
 @item @var{rc_lookahead}
 g_lag_in_frames
 @end table

 @item vp8flags error_resilient
 g_error_resilient

 @end table

 For more information about libvpx see:
 @url{http://www.webmproject.org/}

 @section libx264

 H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10 format supported through
 libx264.

 Requires the presence of the libx264 headers and library during
 configuration. You need to explicitly configure the build with
 @code{--enable-libx264}.

 @subsection Options

 @table @option

 @item preset @var{preset_name}
 Set the encoding preset.

 @item tune @var{tune_name}
 Tune the encoding params.

 @item fastfirstpass @var{bool}
 Use fast settings when encoding first pass, default value is 1.

 @item profile @var{profile_name}
 Set profile restrictions.

 @item level @var{level}
 Specify level (as defined by Annex A).
 Deprecated in favor of @var{x264opts}.

 @item passlogfile @var{filename}
 Specify filename for 2 pass stats.
 Deprecated in favor of @var{x264opts} (see @var{stats} libx264 option).

 @item wpredp @var{wpred_type}
 Specify Weighted prediction for P-frames.
 Deprecated in favor of @var{x264opts} (see @var{weightp} libx264 option).

 @item x264opts @var{options}
 Allow to set any x264 option, see x264 --fullhelp for a list.

 @var{options} is a list of @var{key}=@var{value} couples separated by
 ":".
 @end table

 For example to specify libx264 encoding options with @command{ffmpeg}:
 @example
 ffmpeg -i foo.mpg -vcodec libx264 -x264opts keyint=123:min-keyint=20 -an out.mkv
 @end example

 For more information about libx264 and the supported options see:
 @url{http://www.videolan.org/developers/x264.html}

 @c man end VIDEO ENCODERS
	@chapter Encoders
	@c man begin ENCODERS

	Encoders are configured elements in FFmpeg which allow the encoding of
	multimedia streams.

	When you configure your FFmpeg build, all the supported native encoders
	are enabled by default. Encoders requiring an external library must be enabled
	manually via the corresponding @code{--enable-lib} option. You can list all
	available encoders using the configure option @code{--list-encoders}.

	You can disable all the encoders with the configure option
	@code{--disable-encoders} and selectively enable / disable single encoders
	with the options @code{--enable-encoder=@var{ENCODER}} /
	@code{--disable-encoder=@var{ENCODER}}.

	The option @code{-codecs} of the ff* tools will display the list of
	enabled encoders.

	@c man end ENCODERS

	@chapter Audio Encoders
	@c man begin AUDIO ENCODERS

	A description of some of the currently available audio encoders
	follows.

	@section ac3 and ac3_fixed

	AC-3 audio encoders.

	These encoders implement part of ATSC A/52:2010 and ETSI TS 102 366, as well as
	the undocumented RealAudio 3 (a.k.a. dnet).

	The @var{ac3} encoder uses floating-point math, while the @var{ac3_fixed}
	encoder only uses fixed-point integer math. This does not mean that one is
	always faster, just that one or the other may be better suited to a
	particular system. The floating-point encoder will generally produce better
	quality audio for a given bitrate. The @var{ac3_fixed} encoder is not the
	default codec for any of the output formats, so it must be specified explicitly
	using the option @code{-acodec ac3_fixed} in order to use it.

	@subsection AC-3 Metadata

	The AC-3 metadata options are used to set parameters that describe the audio,
	but in most cases do not affect the audio encoding itself. Some of the options
	do directly affect or influence the decoding and playback of the resulting
	bitstream, while others are just for informational purposes. A few of the
	options will add bits to the output stream that could otherwise be used for
	audio data, and will thus affect the quality of the output. Those will be
	indicated accordingly with a note in the option list below.

	These parameters are described in detail in several publicly-available
	documents.
	@itemize
	@item @uref{http://www.atsc.org/cms/standards/a_52-2010.pdf,A/52:2010 - Digital Audio Compression (AC-3) (E-AC-3) Standard}
	@item @uref{http://www.atsc.org/cms/standards/a_54a_with_corr_1.pdf,A/54 - Guide to the Use of the ATSC Digital Television Standard}
	@item @uref{http://www.dolby.com/uploadedFiles/zz-_Shared_Assets/English_PDFs/Professional/18_Metadata.Guide.pdf,Dolby Metadata Guide}
	@item @uref{http://www.dolby.com/uploadedFiles/zz-_Shared_Assets/English_PDFs/Professional/46_DDEncodingGuidelines.pdf,Dolby Digital Professional Encoding Guidelines}
	@end itemize

	@subsubsection Metadata Control Options

	@table @option

	@item -per_frame_metadata @var{boolean}
	Allow Per-Frame Metadata. Specifies if the encoder should check for changing
	metadata for each frame.
	@table @option
	@item 0
	The metadata values set at initialization will be used for every frame in the
	stream. (default)
	@item 1
	Metadata values can be changed before encoding each frame.
	@end table

	@end table

	@subsubsection Downmix Levels

	@table @option

	@item -center_mixlev @var{level}
	Center Mix Level. The amount of gain the decoder should apply to the center
	channel when downmixing to stereo. This field will only be written to the
	bitstream if a center channel is present. The value is specified as a scale
	factor. There are 3 valid values:
	@table @option
	@item 0.707
	Apply -3dB gain
	@item 0.595
	Apply -4.5dB gain (default)
	@item 0.500
	Apply -6dB gain
	@end table

	@item -surround_mixlev @var{level}
	Surround Mix Level. The amount of gain the decoder should apply to the surround
	channel(s) when downmixing to stereo. This field will only be written to the
	bitstream if one or more surround channels are present. The value is specified
	as a scale factor. There are 3 valid values:
	@table @option
	@item 0.707
	Apply -3dB gain
	@item 0.500
	Apply -6dB gain (default)
	@item 0.000
	Silence Surround Channel(s)
	@end table

	@end table

	@subsubsection Audio Production Information
	Audio Production Information is optional information describing the mixing
	environment. Either none or both of the fields are written to the bitstream.

	@table @option

	@item -mixing_level @var{number}
	Mixing Level. Specifies peak sound pressure level (SPL) in the production
	environment when the mix was mastered. Valid values are 80 to 111, or -1 for
	unknown or not indicated. The default value is -1, but that value cannot be
	used if the Audio Production Information is written to the bitstream. Therefore,
	if the @code{room_type} option is not the default value, the @code{mixing_level}
	option must not be -1.

	@item -room_type @var{type}
	Room Type. Describes the equalization used during the final mixing session at
	the studio or on the dubbing stage. A large room is a dubbing stage with the
	industry standard X-curve equalization; a small room has flat equalization.
	This field will not be written to the bitstream if both the @code{mixing_level}
	option and the @code{room_type} option have the default values.
	@table @option
	@item 0
	@itemx notindicated
	Not Indicated (default)
	@item 1
	@itemx large
	Large Room
	@item 2
	@itemx small
	Small Room
	@end table

	@end table

	@subsubsection Other Metadata Options

	@table @option

	@item -copyright @var{boolean}
	Copyright Indicator. Specifies whether a copyright exists for this audio.
	@table @option
	@item 0
	@itemx off
	No Copyright Exists (default)
	@item 1
	@itemx on
	Copyright Exists
	@end table

	@item -dialnorm @var{value}
	Dialogue Normalization. Indicates how far the average dialogue level of the
	program is below digital 100% full scale (0 dBFS). This parameter determines a
	level shift during audio reproduction that sets the average volume of the
	dialogue to a preset level. The goal is to match volume level between program
	sources. A value of -31dB will result in no volume level change, relative to
	the source volume, during audio reproduction. Valid values are whole numbers in
	the range -31 to -1, with -31 being the default.

	@item -dsur_mode @var{mode}
	Dolby Surround Mode. Specifies whether the stereo signal uses Dolby Surround
	(Pro Logic). This field will only be written to the bitstream if the audio
	stream is stereo. Using this option does @b{NOT} mean the encoder will actually
	apply Dolby Surround processing.
	@table @option
	@item 0
	@itemx notindicated
	Not Indicated (default)
	@item 1
	@itemx off
	Not Dolby Surround Encoded
	@item 2
	@itemx on
	Dolby Surround Encoded
	@end table

	@item -original @var{boolean}
	Original Bit Stream Indicator. Specifies whether this audio is from the
	original source and not a copy.
	@table @option
	@item 0
	@itemx off
	Not Original Source
	@item 1
	@itemx on
	Original Source (default)
	@end table

	@end table

	@subsection Extended Bitstream Information
	The extended bitstream options are part of the Alternate Bit Stream Syntax as
	specified in Annex D of the A/52:2010 standard. It is grouped into 2 parts.
	If any one parameter in a group is specified, all values in that group will be
	written to the bitstream. Default values are used for those that are written
	but have not been specified. If the mixing levels are written, the decoder
	will use these values instead of the ones specified in the @code{center_mixlev}
	and @code{surround_mixlev} options if it supports the Alternate Bit Stream
	Syntax.

	@subsubsection Extended Bitstream Information - Part 1

	@table @option

	@item -dmix_mode @var{mode}
	Preferred Stereo Downmix Mode. Allows the user to select either Lt/Rt
	(Dolby Surround) or Lo/Ro (normal stereo) as the preferred stereo downmix mode.
	@table @option
	@item 0
	@itemx notindicated
	Not Indicated (default)
	@item 1
	@itemx ltrt
	Lt/Rt Downmix Preferred
	@item 2
	@itemx loro
	Lo/Ro Downmix Preferred
	@end table

	@item -ltrt_cmixlev @var{level}
	Lt/Rt Center Mix Level. The amount of gain the decoder should apply to the
	center channel when downmixing to stereo in Lt/Rt mode.
	@table @option
	@item 1.414
	Apply +3dB gain
	@item 1.189
	Apply +1.5dB gain
	@item 1.000
	Apply 0dB gain
	@item 0.841
	Apply -1.5dB gain
	@item 0.707
	Apply -3.0dB gain
	@item 0.595
	Apply -4.5dB gain (default)
	@item 0.500
	Apply -6.0dB gain
	@item 0.000
	Silence Center Channel
	@end table

	@item -ltrt_surmixlev @var{level}
	Lt/Rt Surround Mix Level. The amount of gain the decoder should apply to the
	surround channel(s) when downmixing to stereo in Lt/Rt mode.
	@table @option
	@item 0.841
	Apply -1.5dB gain
	@item 0.707
	Apply -3.0dB gain
	@item 0.595
	Apply -4.5dB gain
	@item 0.500
	Apply -6.0dB gain (default)
	@item 0.000
	Silence Surround Channel(s)
	@end table

	@item -loro_cmixlev @var{level}
	Lo/Ro Center Mix Level. The amount of gain the decoder should apply to the
	center channel when downmixing to stereo in Lo/Ro mode.
	@table @option
	@item 1.414
	Apply +3dB gain
	@item 1.189
	Apply +1.5dB gain
	@item 1.000
	Apply 0dB gain
	@item 0.841
	Apply -1.5dB gain
	@item 0.707
	Apply -3.0dB gain
	@item 0.595
	Apply -4.5dB gain (default)
	@item 0.500
	Apply -6.0dB gain
	@item 0.000
	Silence Center Channel
	@end table

	@item -loro_surmixlev @var{level}
	Lo/Ro Surround Mix Level. The amount of gain the decoder should apply to the
	surround channel(s) when downmixing to stereo in Lo/Ro mode.
	@table @option
	@item 0.841
	Apply -1.5dB gain
	@item 0.707
	Apply -3.0dB gain
	@item 0.595
	Apply -4.5dB gain
	@item 0.500
	Apply -6.0dB gain (default)
	@item 0.000
	Silence Surround Channel(s)
	@end table

	@end table

	@subsubsection Extended Bitstream Information - Part 2

	@table @option

	@item -dsurex_mode @var{mode}
	Dolby Surround EX Mode. Indicates whether the stream uses Dolby Surround EX
	(7.1 matrixed to 5.1). Using this option does @b{NOT} mean the encoder will actually
	apply Dolby Surround EX processing.
	@table @option
	@item 0
	@itemx notindicated
	Not Indicated (default)
	@item 1
	@itemx on
	Dolby Surround EX Off
	@item 2
	@itemx off
	Dolby Surround EX On
	@end table

	@item -dheadphone_mode @var{mode}
	Dolby Headphone Mode. Indicates whether the stream uses Dolby Headphone
	encoding (multi-channel matrixed to 2.0 for use with headphones). Using this
	option does @b{NOT} mean the encoder will actually apply Dolby Headphone
	processing.
	@table @option
	@item 0
	@itemx notindicated
	Not Indicated (default)
	@item 1
	@itemx on
	Dolby Headphone Off
	@item 2
	@itemx off
	Dolby Headphone On
	@end table

	@item -ad_conv_type @var{type}
	A/D Converter Type. Indicates whether the audio has passed through HDCD A/D
	conversion.
	@table @option
	@item 0
	@itemx standard
	Standard A/D Converter (default)
	@item 1
	@itemx hdcd
	HDCD A/D Converter
	@end table

	@end table

	@subsection Other AC-3 Encoding Options

	@table @option

	@item -stereo_rematrixing @var{boolean}
	Stereo Rematrixing. Enables/Disables use of rematrixing for stereo input. This
	is an optional AC-3 feature that increases quality by selectively encoding
	the left/right channels as mid/side. This option is enabled by default, and it
	is highly recommended that it be left as enabled except for testing purposes.

	@end table

	@subsection Floating-Point-Only AC-3 Encoding Options

	These options are only valid for the floating-point encoder and do not exist
	for the fixed-point encoder due to the corresponding features not being
	implemented in fixed-point.

	@table @option

	@item -channel_coupling @var{boolean}
	Enables/Disables use of channel coupling, which is an optional AC-3 feature
	that increases quality by combining high frequency information from multiple
	channels into a single channel. The per-channel high frequency information is
	sent with less accuracy in both the frequency and time domains. This allows
	more bits to be used for lower frequencies while preserving enough information
	to reconstruct the high frequencies. This option is enabled by default for the
	floating-point encoder and should generally be left as enabled except for
	testing purposes or to increase encoding speed.
	@table @option
	@item -1
	@itemx auto
	Selected by Encoder (default)
	@item 0
	@itemx off
	Disable Channel Coupling
	@item 1
	@itemx on
	Enable Channel Coupling
	@end table

	@item -cpl_start_band @var{number}
	Coupling Start Band. Sets the channel coupling start band, from 1 to 15. If a
	value higher than the bandwidth is used, it will be reduced to 1 less than the
	coupling end band. If @var{auto} is used, the start band will be determined by
	the encoder based on the bit rate, sample rate, and channel layout. This option
	has no effect if channel coupling is disabled.
	@table @option
	@item -1
	@itemx auto
	Selected by Encoder (default)
	@end table

	@end table

	@c man end AUDIO ENCODERS

	@chapter Video Encoders
	@c man begin VIDEO ENCODERS

	A description of some of the currently available video encoders
	follows.

	@section libvpx

	VP8 format supported through libvpx.

	Requires the presence of the libvpx headers and library during configuration.
	You need to explicitly configure the build with @code{--enable-libvpx}.

	@subsection Options

	Mapping from FFmpeg to libvpx options with conversion notes in parentheses.

	@table @option

	@item threads
	g_threads

	@item profile
	g_profile

	@item vb
	rc_target_bitrate

	@item g
	kf_max_dist

	@item keyint_min
	kf_min_dist

	@item qmin
	rc_min_quantizer

	@item qmax
	rc_max_quantizer

	@item bufsize, vb
	rc_buf_sz
	@code{(bufsize * 1000 / vb)}

	rc_buf_optimal_sz
	@code{(bufsize * 1000 / vb * 5 / 6)}

	@item rc_init_occupancy, vb
	rc_buf_initial_sz
	@code{(rc_init_occupancy * 1000 / vb)}

	@item rc_buffer_aggressivity
	rc_undershoot_pct

	@item skip_threshold
	rc_dropframe_thresh

	@item qcomp
	rc_2pass_vbr_bias_pct

	@item maxrate, vb
	rc_2pass_vbr_maxsection_pct
	@code{(maxrate * 100 / vb)}

	@item minrate, vb
	rc_2pass_vbr_minsection_pct
	@code{(minrate * 100 / vb)}

	@item minrate, maxrate, vb
	@code{VPX_CBR}
	@code{(minrate == maxrate == vb)}

	@item crf
	@code{VPX_CQ}, @code{VP8E_SET_CQ_LEVEL}

	@item quality
	@table @option
	@item @var{best}
	@code{VPX_DL_BEST_QUALITY}
	@item @var{good}
	@code{VPX_DL_GOOD_QUALITY}
	@item @var{realtime}
	@code{VPX_DL_REALTIME}
	@end table

	@item speed
	@code{VP8E_SET_CPUUSED}

	@item nr
	@code{VP8E_SET_NOISE_SENSITIVITY}

	@item mb_threshold
	@code{VP8E_SET_STATIC_THRESHOLD}

	@item slices
	@code{VP8E_SET_TOKEN_PARTITIONS}

	@item Alternate reference frame related
	@table @option
	@item vp8flags altref
	@code{VP8E_SET_ENABLEAUTOALTREF}
	@item @var{arnr_max_frames}
	@code{VP8E_SET_ARNR_MAXFRAMES}
	@item @var{arnr_type}
	@code{VP8E_SET_ARNR_TYPE}
	@item @var{arnr_strength}
	@code{VP8E_SET_ARNR_STRENGTH}
	@item @var{rc_lookahead}
	g_lag_in_frames
	@end table

	@item vp8flags error_resilient
	g_error_resilient

	@end table

	For more information about libvpx see:
	@url{http://www.webmproject.org/}

	@section libx264

	H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10 format supported through
	libx264.

	Requires the presence of the libx264 headers and library during
	configuration. You need to explicitly configure the build with
	@code{--enable-libx264}.

	@subsection Options

	@table @option

	@item preset @var{preset_name}
	Set the encoding preset.

	@item tune @var{tune_name}
	Tune the encoding params.

	@item fastfirstpass @var{bool}
	Use fast settings when encoding first pass, default value is 1.

	@item profile @var{profile_name}
	Set profile restrictions.

	@item level @var{level}
	Specify level (as defined by Annex A).
	Deprecated in favor of @var{x264opts}.

	@item passlogfile @var{filename}
	Specify filename for 2 pass stats.
	Deprecated in favor of @var{x264opts} (see @var{stats} libx264 option).

	@item wpredp @var{wpred_type}
	Specify Weighted prediction for P-frames.
	Deprecated in favor of @var{x264opts} (see @var{weightp} libx264 option).

	@item x264opts @var{options}
	Allow to set any x264 option, see x264 --fullhelp for a list.

	@var{options} is a list of @var{key}=@var{value} couples separated by
	":".
	@end table

	For example to specify libx264 encoding options with @command{ffmpeg}:
	@example
	ffmpeg -i foo.mpg -vcodec libx264 -x264opts keyint=123:min-keyint=20 -an out.mkv
	@end example

	For more information about libx264 and the supported options see:
	@url{http://www.videolan.org/developers/x264.html}

	@c man end VIDEO ENCODERS