755 lines
22 KiB
Plaintext
755 lines
22 KiB
Plaintext
@chapter Encoders
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@c man begin ENCODERS
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Encoders are configured elements in Libav which allow the encoding of
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multimedia streams.
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When you configure your Libav build, all the supported native encoders
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are enabled by default. Encoders requiring an external library must be enabled
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manually via the corresponding @code{--enable-lib} option. You can list all
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available encoders using the configure option @code{--list-encoders}.
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You can disable all the encoders with the configure option
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@code{--disable-encoders} and selectively enable / disable single encoders
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with the options @code{--enable-encoder=@var{ENCODER}} /
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@code{--disable-encoder=@var{ENCODER}}.
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The option @code{-codecs} of the av* tools will display the list of
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enabled encoders.
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@c man end ENCODERS
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@chapter Audio Encoders
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@c man begin AUDIO ENCODERS
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A description of some of the currently available audio encoders
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follows.
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@section ac3 and ac3_fixed
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AC-3 audio encoders.
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These encoders implement part of ATSC A/52:2010 and ETSI TS 102 366, as well as
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the undocumented RealAudio 3 (a.k.a. dnet).
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The @var{ac3} encoder uses floating-point math, while the @var{ac3_fixed}
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encoder only uses fixed-point integer math. This does not mean that one is
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always faster, just that one or the other may be better suited to a
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particular system. The floating-point encoder will generally produce better
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quality audio for a given bitrate. The @var{ac3_fixed} encoder is not the
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default codec for any of the output formats, so it must be specified explicitly
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using the option @code{-acodec ac3_fixed} in order to use it.
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@subsection AC-3 Metadata
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The AC-3 metadata options are used to set parameters that describe the audio,
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but in most cases do not affect the audio encoding itself. Some of the options
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do directly affect or influence the decoding and playback of the resulting
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bitstream, while others are just for informational purposes. A few of the
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options will add bits to the output stream that could otherwise be used for
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audio data, and will thus affect the quality of the output. Those will be
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indicated accordingly with a note in the option list below.
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These parameters are described in detail in several publicly-available
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documents.
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@itemize
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@item @uref{http://www.atsc.org/cms/standards/a_52-2010.pdf,A/52:2010 - Digital Audio Compression (AC-3) (E-AC-3) Standard}
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@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}
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@item @uref{http://www.dolby.com/uploadedFiles/zz-_Shared_Assets/English_PDFs/Professional/18_Metadata.Guide.pdf,Dolby Metadata Guide}
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@item @uref{http://www.dolby.com/uploadedFiles/zz-_Shared_Assets/English_PDFs/Professional/46_DDEncodingGuidelines.pdf,Dolby Digital Professional Encoding Guidelines}
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@end itemize
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@subsubsection Metadata Control Options
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@table @option
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@item -per_frame_metadata @var{boolean}
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Allow Per-Frame Metadata. Specifies if the encoder should check for changing
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metadata for each frame.
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@table @option
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@item 0
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The metadata values set at initialization will be used for every frame in the
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stream. (default)
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@item 1
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Metadata values can be changed before encoding each frame.
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@end table
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@end table
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@subsubsection Downmix Levels
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@table @option
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@item -center_mixlev @var{level}
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Center Mix Level. The amount of gain the decoder should apply to the center
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channel when downmixing to stereo. This field will only be written to the
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bitstream if a center channel is present. The value is specified as a scale
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factor. There are 3 valid values:
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@table @option
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@item 0.707
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Apply -3dB gain
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@item 0.595
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Apply -4.5dB gain (default)
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@item 0.500
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Apply -6dB gain
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@end table
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@item -surround_mixlev @var{level}
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Surround Mix Level. The amount of gain the decoder should apply to the surround
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channel(s) when downmixing to stereo. This field will only be written to the
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bitstream if one or more surround channels are present. The value is specified
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as a scale factor. There are 3 valid values:
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@table @option
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@item 0.707
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Apply -3dB gain
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@item 0.500
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Apply -6dB gain (default)
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@item 0.000
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Silence Surround Channel(s)
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@end table
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@end table
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@subsubsection Audio Production Information
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Audio Production Information is optional information describing the mixing
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environment. Either none or both of the fields are written to the bitstream.
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@table @option
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@item -mixing_level @var{number}
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Mixing Level. Specifies peak sound pressure level (SPL) in the production
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environment when the mix was mastered. Valid values are 80 to 111, or -1 for
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unknown or not indicated. The default value is -1, but that value cannot be
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used if the Audio Production Information is written to the bitstream. Therefore,
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if the @code{room_type} option is not the default value, the @code{mixing_level}
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option must not be -1.
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@item -room_type @var{type}
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Room Type. Describes the equalization used during the final mixing session at
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the studio or on the dubbing stage. A large room is a dubbing stage with the
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industry standard X-curve equalization; a small room has flat equalization.
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This field will not be written to the bitstream if both the @code{mixing_level}
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option and the @code{room_type} option have the default values.
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@table @option
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@item 0
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@itemx notindicated
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Not Indicated (default)
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@item 1
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@itemx large
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Large Room
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@item 2
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@itemx small
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Small Room
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@end table
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@end table
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@subsubsection Other Metadata Options
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@table @option
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@item -copyright @var{boolean}
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Copyright Indicator. Specifies whether a copyright exists for this audio.
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@table @option
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@item 0
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@itemx off
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No Copyright Exists (default)
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@item 1
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@itemx on
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Copyright Exists
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@end table
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@item -dialnorm @var{value}
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Dialogue Normalization. Indicates how far the average dialogue level of the
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program is below digital 100% full scale (0 dBFS). This parameter determines a
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level shift during audio reproduction that sets the average volume of the
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dialogue to a preset level. The goal is to match volume level between program
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sources. A value of -31dB will result in no volume level change, relative to
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the source volume, during audio reproduction. Valid values are whole numbers in
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the range -31 to -1, with -31 being the default.
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@item -dsur_mode @var{mode}
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Dolby Surround Mode. Specifies whether the stereo signal uses Dolby Surround
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(Pro Logic). This field will only be written to the bitstream if the audio
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stream is stereo. Using this option does @b{NOT} mean the encoder will actually
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apply Dolby Surround processing.
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@table @option
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@item 0
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@itemx notindicated
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Not Indicated (default)
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@item 1
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@itemx off
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Not Dolby Surround Encoded
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@item 2
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@itemx on
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Dolby Surround Encoded
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@end table
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@item -original @var{boolean}
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Original Bit Stream Indicator. Specifies whether this audio is from the
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original source and not a copy.
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@table @option
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@item 0
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@itemx off
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Not Original Source
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@item 1
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@itemx on
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Original Source (default)
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@end table
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@end table
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@subsection Extended Bitstream Information
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The extended bitstream options are part of the Alternate Bit Stream Syntax as
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specified in Annex D of the A/52:2010 standard. It is grouped into 2 parts.
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If any one parameter in a group is specified, all values in that group will be
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written to the bitstream. Default values are used for those that are written
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but have not been specified. If the mixing levels are written, the decoder
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will use these values instead of the ones specified in the @code{center_mixlev}
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and @code{surround_mixlev} options if it supports the Alternate Bit Stream
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Syntax.
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@subsubsection Extended Bitstream Information - Part 1
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@table @option
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@item -dmix_mode @var{mode}
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Preferred Stereo Downmix Mode. Allows the user to select either Lt/Rt
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(Dolby Surround) or Lo/Ro (normal stereo) as the preferred stereo downmix mode.
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@table @option
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@item 0
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@itemx notindicated
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Not Indicated (default)
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@item 1
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@itemx ltrt
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Lt/Rt Downmix Preferred
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@item 2
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@itemx loro
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Lo/Ro Downmix Preferred
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@end table
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@item -ltrt_cmixlev @var{level}
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Lt/Rt Center Mix Level. The amount of gain the decoder should apply to the
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center channel when downmixing to stereo in Lt/Rt mode.
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@table @option
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@item 1.414
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Apply +3dB gain
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@item 1.189
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Apply +1.5dB gain
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@item 1.000
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Apply 0dB gain
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@item 0.841
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Apply -1.5dB gain
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@item 0.707
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Apply -3.0dB gain
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@item 0.595
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Apply -4.5dB gain (default)
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@item 0.500
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Apply -6.0dB gain
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@item 0.000
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Silence Center Channel
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@end table
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@item -ltrt_surmixlev @var{level}
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Lt/Rt Surround Mix Level. The amount of gain the decoder should apply to the
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surround channel(s) when downmixing to stereo in Lt/Rt mode.
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@table @option
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@item 0.841
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Apply -1.5dB gain
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@item 0.707
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Apply -3.0dB gain
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@item 0.595
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Apply -4.5dB gain
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@item 0.500
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Apply -6.0dB gain (default)
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@item 0.000
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Silence Surround Channel(s)
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@end table
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@item -loro_cmixlev @var{level}
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Lo/Ro Center Mix Level. The amount of gain the decoder should apply to the
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center channel when downmixing to stereo in Lo/Ro mode.
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@table @option
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@item 1.414
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Apply +3dB gain
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@item 1.189
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Apply +1.5dB gain
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@item 1.000
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Apply 0dB gain
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@item 0.841
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Apply -1.5dB gain
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@item 0.707
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Apply -3.0dB gain
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@item 0.595
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Apply -4.5dB gain (default)
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@item 0.500
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Apply -6.0dB gain
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@item 0.000
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Silence Center Channel
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@end table
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@item -loro_surmixlev @var{level}
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Lo/Ro Surround Mix Level. The amount of gain the decoder should apply to the
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surround channel(s) when downmixing to stereo in Lo/Ro mode.
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@table @option
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@item 0.841
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Apply -1.5dB gain
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@item 0.707
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Apply -3.0dB gain
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@item 0.595
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Apply -4.5dB gain
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@item 0.500
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Apply -6.0dB gain (default)
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@item 0.000
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Silence Surround Channel(s)
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@end table
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@end table
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@subsubsection Extended Bitstream Information - Part 2
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@table @option
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@item -dsurex_mode @var{mode}
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Dolby Surround EX Mode. Indicates whether the stream uses Dolby Surround EX
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(7.1 matrixed to 5.1). Using this option does @b{NOT} mean the encoder will actually
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apply Dolby Surround EX processing.
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@table @option
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@item 0
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@itemx notindicated
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Not Indicated (default)
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@item 1
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@itemx on
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Dolby Surround EX Off
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@item 2
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@itemx off
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Dolby Surround EX On
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@end table
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@item -dheadphone_mode @var{mode}
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Dolby Headphone Mode. Indicates whether the stream uses Dolby Headphone
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encoding (multi-channel matrixed to 2.0 for use with headphones). Using this
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option does @b{NOT} mean the encoder will actually apply Dolby Headphone
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processing.
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@table @option
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@item 0
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@itemx notindicated
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Not Indicated (default)
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@item 1
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@itemx on
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Dolby Headphone Off
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@item 2
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@itemx off
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Dolby Headphone On
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@end table
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@item -ad_conv_type @var{type}
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A/D Converter Type. Indicates whether the audio has passed through HDCD A/D
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conversion.
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@table @option
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@item 0
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@itemx standard
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Standard A/D Converter (default)
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@item 1
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@itemx hdcd
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HDCD A/D Converter
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@end table
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@end table
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@subsection Other AC-3 Encoding Options
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@table @option
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@item -stereo_rematrixing @var{boolean}
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Stereo Rematrixing. Enables/Disables use of rematrixing for stereo input. This
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is an optional AC-3 feature that increases quality by selectively encoding
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the left/right channels as mid/side. This option is enabled by default, and it
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is highly recommended that it be left as enabled except for testing purposes.
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@end table
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@subheading Floating-Point-Only AC-3 Encoding Options
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These options are only valid for the floating-point encoder and do not exist
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for the fixed-point encoder due to the corresponding features not being
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implemented in fixed-point.
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@table @option
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@item -channel_coupling @var{boolean}
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Enables/Disables use of channel coupling, which is an optional AC-3 feature
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that increases quality by combining high frequency information from multiple
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channels into a single channel. The per-channel high frequency information is
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sent with less accuracy in both the frequency and time domains. This allows
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more bits to be used for lower frequencies while preserving enough information
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to reconstruct the high frequencies. This option is enabled by default for the
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floating-point encoder and should generally be left as enabled except for
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testing purposes or to increase encoding speed.
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@table @option
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@item -1
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@itemx auto
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Selected by Encoder (default)
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@item 0
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@itemx off
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Disable Channel Coupling
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@item 1
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@itemx on
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Enable Channel Coupling
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@end table
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@item -cpl_start_band @var{number}
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Coupling Start Band. Sets the channel coupling start band, from 1 to 15. If a
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value higher than the bandwidth is used, it will be reduced to 1 less than the
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coupling end band. If @var{auto} is used, the start band will be determined by
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the encoder based on the bit rate, sample rate, and channel layout. This option
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has no effect if channel coupling is disabled.
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@table @option
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@item -1
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@itemx auto
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Selected by Encoder (default)
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@end table
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@end table
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@section libwavpack
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A wrapper providing WavPack encoding through libwavpack.
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Only lossless mode using 32-bit integer samples is supported currently.
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The @option{compression_level} option can be used to control speed vs.
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compression tradeoff, with the values mapped to libwavpack as follows:
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@table @option
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@item 0
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Fast mode - corresponding to the wavpack @option{-f} option.
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@item 1
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Normal (default) settings.
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@item 2
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High quality - corresponding to the wavpack @option{-h} option.
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@item 3
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Very high quality - corresponding to the wavpack @option{-hh} option.
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@item 4-8
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Same as 3, but with extra processing enabled - corresponding to the wavpack
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@option{-x} option. I.e. 4 is the same as @option{-x2} and 8 is the same as
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@option{-x6}.
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@end table
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@c man end AUDIO ENCODERS
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@chapter Video Encoders
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@c man begin VIDEO ENCODERS
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@section libwebp
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libwebp WebP Image encoder wrapper
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libwebp is Google's official encoder for WebP images. It can encode in either
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lossy or lossless mode. Lossy images are essentially a wrapper around a VP8
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frame. Lossless images are a separate codec developed by Google.
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@subsection Pixel Format
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Currently, libwebp only supports YUV420 for lossy and RGB for lossless due
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to limitations of the format and libwebp. Alpha is supported for either mode.
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Because of API limitations, if RGB is passed in when encoding lossy or YUV is
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passed in for encoding lossless, the pixel format will automatically be
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converted using functions from libwebp. This is not ideal and is done only for
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convenience.
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@subsection Options
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@table @option
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@item -lossless @var{boolean}
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Enables/Disables use of lossless mode. Default is 0.
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@item -compression_level @var{integer}
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For lossy, this is a quality/speed tradeoff. Higher values give better quality
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for a given size at the cost of increased encoding time. For lossless, this is
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a size/speed tradeoff. Higher values give smaller size at the cost of increased
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encoding time. More specifically, it controls the number of extra algorithms
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and compression tools used, and varies the combination of these tools. This
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maps to the @var{method} option in libwebp. The valid range is 0 to 6.
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Default is 4.
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@item -qscale @var{float}
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For lossy encoding, this controls image quality, 0 to 100. For lossless
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encoding, this controls the effort and time spent at compressing more. The
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default value is 75. Note that for usage via libavcodec, this option is called
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@var{global_quality} and must be multiplied by @var{FF_QP2LAMBDA}.
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@item -preset @var{type}
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Configuration preset. This does some automatic settings based on the general
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type of the image.
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@table @option
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@item none
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Do not use a preset.
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@item default
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Use the encoder default.
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@item picture
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Digital picture, like portrait, inner shot
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@item photo
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Outdoor photograph, with natural lighting
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@item drawing
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Hand or line drawing, with high-contrast details
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@item icon
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Small-sized colorful images
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@item text
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Text-like
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@end table
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@end table
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@section libx264
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x264 H.264/MPEG-4 AVC encoder wrapper
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x264 supports an impressive number of features, including 8x8 and 4x4 adaptive
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spatial transform, adaptive B-frame placement, CAVLC/CABAC entropy coding,
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interlacing (MBAFF), lossless mode, psy optimizations for detail retention
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(adaptive quantization, psy-RD, psy-trellis).
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The Libav wrapper provides a mapping for most of them using global options
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that match those of the encoders and provides private options for the unique
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encoder options. Additionally an expert override is provided to directly pass
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a list of key=value tuples as accepted by x264_param_parse.
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@subsection Option Mapping
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The following options are supported by the x264 wrapper, the x264-equivalent
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options follow the Libav ones.
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@multitable @columnfractions .2 .2
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@item b @tab bitrate
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Libav @code{b} option is expressed in bits/s, x264 @code{bitrate} in kilobits/s.
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@item bf @tab bframes
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Maximum number of B-frames.
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@item g @tab keyint
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Maximum GOP size.
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@item qmin @tab qpmin
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@item qmax @tab qpmax
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@item qdiff @tab qpstep
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@item qblur @tab qblur
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@item qcomp @tab qcomp
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@item refs @tab ref
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@item sc_threshold @tab scenecut
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@item trellis @tab trellis
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@item nr @tab nr
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Noise reduction.
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@item me_range @tab merange
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@item me_method @tab me
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@item subq @tab subme
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@item b_strategy @tab b-adapt
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@item keyint_min @tab keyint-min
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@item coder @tab cabac
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Set coder to @code{ac} to use CABAC.
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@item cmp @tab chroma-me
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Set to @code{chroma} to use chroma motion estimation.
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@item threads @tab threads
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@item thread_type @tab sliced_threads
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Set to @code{slice} to use sliced threading instead of frame threading.
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@item flags -cgop @tab open-gop
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Set @code{-cgop} to use recovery points to close GOPs.
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@item rc_init_occupancy @tab vbv-init
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Initial buffer occupancy.
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@end multitable
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@subsection Private Options
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@table @option
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@item -preset @var{string}
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Set the encoding preset (cf. x264 --fullhelp).
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@item -tune @var{string}
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Tune the encoding params (cf. x264 --fullhelp).
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@item -profile @var{string}
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Set profile restrictions (cf. x264 --fullhelp).
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@item -fastfirstpass @var{integer}
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Use fast settings when encoding first pass.
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@item -crf @var{float}
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Select the quality for constant quality mode.
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@item -crf_max @var{float}
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In CRF mode, prevents VBV from lowering quality beyond this point.
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@item -qp @var{integer}
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Constant quantization parameter rate control method.
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@item -aq-mode @var{integer}
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AQ method
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Possible values:
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@table @samp
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@item none
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@item variance
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Variance AQ (complexity mask).
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@item autovariance
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Auto-variance AQ (experimental).
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@end table
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@item -aq-strength @var{float}
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AQ strength, reduces blocking and blurring in flat and textured areas.
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@item -psy @var{integer}
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Use psychovisual optimizations.
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@item -psy-rd @var{string}
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Strength of psychovisual optimization, in <psy-rd>:<psy-trellis> format.
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@item -rc-lookahead @var{integer}
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Number of frames to look ahead for frametype and ratecontrol.
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@item -weightb @var{integer}
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Weighted prediction for B-frames.
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@item -weightp @var{integer}
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Weighted prediction analysis method.
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Possible values:
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@table @samp
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@item none
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@item simple
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@item smart
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@end table
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@item -ssim @var{integer}
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Calculate and print SSIM stats.
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@item -intra-refresh @var{integer}
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Use Periodic Intra Refresh instead of IDR frames.
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@item -bluray-compat @var{integer}
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Configure the encoder to be compatible with the bluray standard.
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It is a shorthand for setting "bluray-compat=1 force-cfr=1".
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@item -b-bias @var{integer}
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Influences how often B-frames are used.
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@item -b-pyramid @var{integer}
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Keep some B-frames as references.
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Possible values:
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@table @samp
|
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@item none
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@item strict
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Strictly hierarchical pyramid.
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@item normal
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Non-strict (not Blu-ray compatible).
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@end table
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@item -mixed-refs @var{integer}
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One reference per partition, as opposed to one reference per macroblock.
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@item -8x8dct @var{integer}
|
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High profile 8x8 transform.
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@item -fast-pskip @var{integer}
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@item -aud @var{integer}
|
|
Use access unit delimiters.
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@item -mbtree @var{integer}
|
|
Use macroblock tree ratecontrol.
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@item -deblock @var{string}
|
|
Loop filter parameters, in <alpha:beta> form.
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@item -cplxblur @var{float}
|
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Reduce fluctuations in QP (before curve compression).
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@item -partitions @var{string}
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A comma-separated list of partitions to consider, possible values: p8x8, p4x4, b8x8, i8x8, i4x4, none, all.
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@item -direct-pred @var{integer}
|
|
Direct MV prediction mode
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|
|
|
Possible values:
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@table @samp
|
|
@item none
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|
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@item spatial
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|
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@item temporal
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|
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@item auto
|
|
|
|
@end table
|
|
@item -slice-max-size @var{integer}
|
|
Limit the size of each slice in bytes.
|
|
@item -stats @var{string}
|
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Filename for 2 pass stats.
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|
@item -nal-hrd @var{integer}
|
|
Signal HRD information (requires vbv-bufsize; cbr not allowed in .mp4).
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|
|
Possible values:
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@table @samp
|
|
@item none
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|
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@item vbr
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|
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@item cbr
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|
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@end table
|
|
@item -x264-params @var{string}
|
|
Override the x264 configuration using a :-separated list of key=value parameters.
|
|
@example
|
|
-x264-params level=30:bframes=0:weightp=0:cabac=0:ref=1:vbv-maxrate=768:vbv-bufsize=2000:analyse=all:me=umh:no-fast-pskip=1:subq=6:8x8dct=0:trellis=0
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@end example
|
|
@end table
|
|
|
|
Encoding avpresets for common usages are provided so they can be used with the
|
|
general presets system (e.g. passing the @code{-pre} option).
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|
|
@section ProRes
|
|
|
|
Apple ProRes encoder.
|
|
|
|
@subsection Private Options
|
|
|
|
@table @option
|
|
@item profile @var{integer}
|
|
Select the ProRes profile to encode
|
|
@table @samp
|
|
@item proxy
|
|
@item lt
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|
@item standard
|
|
@item hq
|
|
@item 4444
|
|
@end table
|
|
|
|
@item quant_mat @var{integer}
|
|
Select quantization matrix.
|
|
@table @samp
|
|
@item auto
|
|
@item default
|
|
@item proxy
|
|
@item lt
|
|
@item standard
|
|
@item hq
|
|
@end table
|
|
If set to @var{auto}, the matrix matching the profile will be picked.
|
|
If not set, the matrix providing the highest quality, @var{default}, will be
|
|
picked.
|
|
|
|
@item bits_per_mb @var{integer}
|
|
How many bits to allot for coding one macroblock. Different profiles use
|
|
between 200 and 2400 bits per macroblock, the maximum is 8000.
|
|
|
|
@item mbs_per_slice @var{integer}
|
|
Number of macroblocks in each slice (1-8); the default value (8)
|
|
should be good in almost all situations.
|
|
|
|
@item vendor @var{string}
|
|
Override the 4-byte vendor ID.
|
|
A custom vendor ID like @var{apl0} would claim the stream was produced by
|
|
the Apple encoder.
|
|
|
|
@item alpha_bits @var{integer}
|
|
Specify number of bits for alpha component.
|
|
Possible values are @var{0}, @var{8} and @var{16}.
|
|
Use @var{0} to disable alpha plane coding.
|
|
|
|
@end table
|
|
|
|
@subsection Speed considerations
|
|
|
|
In the default mode of operation the encoder has to honor frame constraints
|
|
(i.e. not produc frames with size bigger than requested) while still making
|
|
output picture as good as possible.
|
|
A frame containing a lot of small details is harder to compress and the encoder
|
|
would spend more time searching for appropriate quantizers for each slice.
|
|
|
|
Setting a higher @option{bits_per_mb} limit will improve the speed.
|
|
|
|
For the fastest encoding speed set the @option{qscale} parameter (4 is the
|
|
recommended value) and do not set a size constraint.
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|
|
|
@c man end VIDEO ENCODERS
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