4 Encoders are configured elements in Libav which allow the encoding of
7 When you configure your Libav build, all the supported native encoders
8 are enabled by default. Encoders requiring an external library must be enabled
9 manually via the corresponding @code{--enable-lib} option. You can list all
10 available encoders using the configure option @code{--list-encoders}.
12 You can disable all the encoders with the configure option
13 @code{--disable-encoders} and selectively enable / disable single encoders
14 with the options @code{--enable-encoder=@var{ENCODER}} /
15 @code{--disable-encoder=@var{ENCODER}}.
17 The option @code{-codecs} of the av* tools will display the list of
22 @chapter Audio Encoders
23 @c man begin AUDIO ENCODERS
25 A description of some of the currently available audio encoders
28 @section ac3 and ac3_fixed
32 These encoders implement part of ATSC A/52:2010 and ETSI TS 102 366, as well as
33 the undocumented RealAudio 3 (a.k.a. dnet).
35 The @var{ac3} encoder uses floating-point math, while the @var{ac3_fixed}
36 encoder only uses fixed-point integer math. This does not mean that one is
37 always faster, just that one or the other may be better suited to a
38 particular system. The floating-point encoder will generally produce better
39 quality audio for a given bitrate. The @var{ac3_fixed} encoder is not the
40 default codec for any of the output formats, so it must be specified explicitly
41 using the option @code{-acodec ac3_fixed} in order to use it.
43 @subsection AC-3 Metadata
45 The AC-3 metadata options are used to set parameters that describe the audio,
46 but in most cases do not affect the audio encoding itself. Some of the options
47 do directly affect or influence the decoding and playback of the resulting
48 bitstream, while others are just for informational purposes. A few of the
49 options will add bits to the output stream that could otherwise be used for
50 audio data, and will thus affect the quality of the output. Those will be
51 indicated accordingly with a note in the option list below.
53 These parameters are described in detail in several publicly-available
56 @item @uref{http://www.atsc.org/cms/standards/a_52-2010.pdf,A/52:2010 - Digital Audio Compression (AC-3) (E-AC-3) Standard}
57 @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}
58 @item @uref{http://www.dolby.com/uploadedFiles/zz-_Shared_Assets/English_PDFs/Professional/18_Metadata.Guide.pdf,Dolby Metadata Guide}
59 @item @uref{http://www.dolby.com/uploadedFiles/zz-_Shared_Assets/English_PDFs/Professional/46_DDEncodingGuidelines.pdf,Dolby Digital Professional Encoding Guidelines}
62 @subsubsection Metadata Control Options
66 @item -per_frame_metadata @var{boolean}
67 Allow Per-Frame Metadata. Specifies if the encoder should check for changing
68 metadata for each frame.
71 The metadata values set at initialization will be used for every frame in the
74 Metadata values can be changed before encoding each frame.
79 @subsubsection Downmix Levels
83 @item -center_mixlev @var{level}
84 Center Mix Level. The amount of gain the decoder should apply to the center
85 channel when downmixing to stereo. This field will only be written to the
86 bitstream if a center channel is present. The value is specified as a scale
87 factor. There are 3 valid values:
92 Apply -4.5dB gain (default)
97 @item -surround_mixlev @var{level}
98 Surround Mix Level. The amount of gain the decoder should apply to the surround
99 channel(s) when downmixing to stereo. This field will only be written to the
100 bitstream if one or more surround channels are present. The value is specified
101 as a scale factor. There are 3 valid values:
106 Apply -6dB gain (default)
108 Silence Surround Channel(s)
113 @subsubsection Audio Production Information
114 Audio Production Information is optional information describing the mixing
115 environment. Either none or both of the fields are written to the bitstream.
119 @item -mixing_level @var{number}
120 Mixing Level. Specifies peak sound pressure level (SPL) in the production
121 environment when the mix was mastered. Valid values are 80 to 111, or -1 for
122 unknown or not indicated. The default value is -1, but that value cannot be
123 used if the Audio Production Information is written to the bitstream. Therefore,
124 if the @code{room_type} option is not the default value, the @code{mixing_level}
125 option must not be -1.
127 @item -room_type @var{type}
128 Room Type. Describes the equalization used during the final mixing session at
129 the studio or on the dubbing stage. A large room is a dubbing stage with the
130 industry standard X-curve equalization; a small room has flat equalization.
131 This field will not be written to the bitstream if both the @code{mixing_level}
132 option and the @code{room_type} option have the default values.
136 Not Indicated (default)
147 @subsubsection Other Metadata Options
151 @item -copyright @var{boolean}
152 Copyright Indicator. Specifies whether a copyright exists for this audio.
156 No Copyright Exists (default)
162 @item -dialnorm @var{value}
163 Dialogue Normalization. Indicates how far the average dialogue level of the
164 program is below digital 100% full scale (0 dBFS). This parameter determines a
165 level shift during audio reproduction that sets the average volume of the
166 dialogue to a preset level. The goal is to match volume level between program
167 sources. A value of -31dB will result in no volume level change, relative to
168 the source volume, during audio reproduction. Valid values are whole numbers in
169 the range -31 to -1, with -31 being the default.
171 @item -dsur_mode @var{mode}
172 Dolby Surround Mode. Specifies whether the stereo signal uses Dolby Surround
173 (Pro Logic). This field will only be written to the bitstream if the audio
174 stream is stereo. Using this option does @b{NOT} mean the encoder will actually
175 apply Dolby Surround processing.
179 Not Indicated (default)
182 Not Dolby Surround Encoded
185 Dolby Surround Encoded
188 @item -original @var{boolean}
189 Original Bit Stream Indicator. Specifies whether this audio is from the
190 original source and not a copy.
197 Original Source (default)
202 @subsection Extended Bitstream Information
203 The extended bitstream options are part of the Alternate Bit Stream Syntax as
204 specified in Annex D of the A/52:2010 standard. It is grouped into 2 parts.
205 If any one parameter in a group is specified, all values in that group will be
206 written to the bitstream. Default values are used for those that are written
207 but have not been specified. If the mixing levels are written, the decoder
208 will use these values instead of the ones specified in the @code{center_mixlev}
209 and @code{surround_mixlev} options if it supports the Alternate Bit Stream
212 @subsubsection Extended Bitstream Information - Part 1
216 @item -dmix_mode @var{mode}
217 Preferred Stereo Downmix Mode. Allows the user to select either Lt/Rt
218 (Dolby Surround) or Lo/Ro (normal stereo) as the preferred stereo downmix mode.
222 Not Indicated (default)
225 Lt/Rt Downmix Preferred
228 Lo/Ro Downmix Preferred
231 @item -ltrt_cmixlev @var{level}
232 Lt/Rt Center Mix Level. The amount of gain the decoder should apply to the
233 center channel when downmixing to stereo in Lt/Rt mode.
246 Apply -4.5dB gain (default)
250 Silence Center Channel
253 @item -ltrt_surmixlev @var{level}
254 Lt/Rt Surround Mix Level. The amount of gain the decoder should apply to the
255 surround channel(s) when downmixing to stereo in Lt/Rt mode.
264 Apply -6.0dB gain (default)
266 Silence Surround Channel(s)
269 @item -loro_cmixlev @var{level}
270 Lo/Ro Center Mix Level. The amount of gain the decoder should apply to the
271 center channel when downmixing to stereo in Lo/Ro mode.
284 Apply -4.5dB gain (default)
288 Silence Center Channel
291 @item -loro_surmixlev @var{level}
292 Lo/Ro Surround Mix Level. The amount of gain the decoder should apply to the
293 surround channel(s) when downmixing to stereo in Lo/Ro mode.
302 Apply -6.0dB gain (default)
304 Silence Surround Channel(s)
309 @subsubsection Extended Bitstream Information - Part 2
313 @item -dsurex_mode @var{mode}
314 Dolby Surround EX Mode. Indicates whether the stream uses Dolby Surround EX
315 (7.1 matrixed to 5.1). Using this option does @b{NOT} mean the encoder will actually
316 apply Dolby Surround EX processing.
320 Not Indicated (default)
323 Dolby Surround EX Off
329 @item -dheadphone_mode @var{mode}
330 Dolby Headphone Mode. Indicates whether the stream uses Dolby Headphone
331 encoding (multi-channel matrixed to 2.0 for use with headphones). Using this
332 option does @b{NOT} mean the encoder will actually apply Dolby Headphone
337 Not Indicated (default)
346 @item -ad_conv_type @var{type}
347 A/D Converter Type. Indicates whether the audio has passed through HDCD A/D
352 Standard A/D Converter (default)
360 @subsection Other AC-3 Encoding Options
364 @item -stereo_rematrixing @var{boolean}
365 Stereo Rematrixing. Enables/Disables use of rematrixing for stereo input. This
366 is an optional AC-3 feature that increases quality by selectively encoding
367 the left/right channels as mid/side. This option is enabled by default, and it
368 is highly recommended that it be left as enabled except for testing purposes.
372 @subheading Floating-Point-Only AC-3 Encoding Options
374 These options are only valid for the floating-point encoder and do not exist
375 for the fixed-point encoder due to the corresponding features not being
376 implemented in fixed-point.
380 @item -channel_coupling @var{boolean}
381 Enables/Disables use of channel coupling, which is an optional AC-3 feature
382 that increases quality by combining high frequency information from multiple
383 channels into a single channel. The per-channel high frequency information is
384 sent with less accuracy in both the frequency and time domains. This allows
385 more bits to be used for lower frequencies while preserving enough information
386 to reconstruct the high frequencies. This option is enabled by default for the
387 floating-point encoder and should generally be left as enabled except for
388 testing purposes or to increase encoding speed.
392 Selected by Encoder (default)
395 Disable Channel Coupling
398 Enable Channel Coupling
401 @item -cpl_start_band @var{number}
402 Coupling Start Band. Sets the channel coupling start band, from 1 to 15. If a
403 value higher than the bandwidth is used, it will be reduced to 1 less than the
404 coupling end band. If @var{auto} is used, the start band will be determined by
405 the encoder based on the bit rate, sample rate, and channel layout. This option
406 has no effect if channel coupling is disabled.
410 Selected by Encoder (default)
417 A wrapper providing WavPack encoding through libwavpack.
419 Only lossless mode using 32-bit integer samples is supported currently.
420 The @option{compression_level} option can be used to control speed vs.
421 compression tradeoff, with the values mapped to libwavpack as follows:
426 Fast mode - corresponding to the wavpack @option{-f} option.
429 Normal (default) settings.
432 High quality - corresponding to the wavpack @option{-h} option.
435 Very high quality - corresponding to the wavpack @option{-hh} option.
438 Same as 3, but with extra processing enabled - corresponding to the wavpack
439 @option{-x} option. I.e. 4 is the same as @option{-x2} and 8 is the same as
444 @c man end AUDIO ENCODERS
446 @chapter Video Encoders
447 @c man begin VIDEO ENCODERS
451 libwebp WebP Image encoder wrapper
453 libwebp is Google's official encoder for WebP images. It can encode in either
454 lossy or lossless mode. Lossy images are essentially a wrapper around a VP8
455 frame. Lossless images are a separate codec developed by Google.
457 @subsection Pixel Format
459 Currently, libwebp only supports YUV420 for lossy and RGB for lossless due
460 to limitations of the format and libwebp. Alpha is supported for either mode.
461 Because of API limitations, if RGB is passed in when encoding lossy or YUV is
462 passed in for encoding lossless, the pixel format will automatically be
463 converted using functions from libwebp. This is not ideal and is done only for
470 @item -lossless @var{boolean}
471 Enables/Disables use of lossless mode. Default is 0.
473 @item -compression_level @var{integer}
474 For lossy, this is a quality/speed tradeoff. Higher values give better quality
475 for a given size at the cost of increased encoding time. For lossless, this is
476 a size/speed tradeoff. Higher values give smaller size at the cost of increased
477 encoding time. More specifically, it controls the number of extra algorithms
478 and compression tools used, and varies the combination of these tools. This
479 maps to the @var{method} option in libwebp. The valid range is 0 to 6.
482 @item -qscale @var{float}
483 For lossy encoding, this controls image quality, 0 to 100. For lossless
484 encoding, this controls the effort and time spent at compressing more. The
485 default value is 75. Note that for usage via libavcodec, this option is called
486 @var{global_quality} and must be multiplied by @var{FF_QP2LAMBDA}.
488 @item -preset @var{type}
489 Configuration preset. This does some automatic settings based on the general
495 Use the encoder default.
497 Digital picture, like portrait, inner shot
499 Outdoor photograph, with natural lighting
501 Hand or line drawing, with high-contrast details
503 Small-sized colorful images
512 x264 H.264/MPEG-4 AVC encoder wrapper
514 x264 supports an impressive number of features, including 8x8 and 4x4 adaptive
515 spatial transform, adaptive B-frame placement, CAVLC/CABAC entropy coding,
516 interlacing (MBAFF), lossless mode, psy optimizations for detail retention
517 (adaptive quantization, psy-RD, psy-trellis).
519 The Libav wrapper provides a mapping for most of them using global options
520 that match those of the encoders and provides private options for the unique
521 encoder options. Additionally an expert override is provided to directly pass
522 a list of key=value tuples as accepted by x264_param_parse.
524 @subsection Option Mapping
526 The following options are supported by the x264 wrapper, the x264-equivalent
527 options follow the Libav ones.
529 @multitable @columnfractions .2 .2
531 Libav @code{b} option is expressed in bits/s, x264 @code{bitrate} in kilobits/s.
532 @item bf @tab bframes
533 Maximum number of B-frames.
536 @item qmin @tab qpmin
537 @item qmax @tab qpmax
538 @item qdiff @tab qpstep
539 @item qblur @tab qblur
540 @item qcomp @tab qcomp
542 @item sc_threshold @tab scenecut
543 @item trellis @tab trellis
546 @item me_range @tab merange
547 @item me_method @tab me
548 @item subq @tab subme
549 @item b_strategy @tab b-adapt
550 @item keyint_min @tab keyint-min
551 @item coder @tab cabac
552 Set coder to @code{ac} to use CABAC.
553 @item cmp @tab chroma-me
554 Set to @code{chroma} to use chroma motion estimation.
555 @item threads @tab threads
556 @item thread_type @tab sliced_threads
557 Set to @code{slice} to use sliced threading instead of frame threading.
558 @item flags -cgop @tab open-gop
559 Set @code{-cgop} to use recovery points to close GOPs.
560 @item rc_init_occupancy @tab vbv-init
561 Initial buffer occupancy.
564 @subsection Private Options
566 @item -preset @var{string}
567 Set the encoding preset (cf. x264 --fullhelp).
568 @item -tune @var{string}
569 Tune the encoding params (cf. x264 --fullhelp).
570 @item -profile @var{string}
571 Set profile restrictions (cf. x264 --fullhelp).
572 @item -fastfirstpass @var{integer}
573 Use fast settings when encoding first pass.
574 @item -crf @var{float}
575 Select the quality for constant quality mode.
576 @item -crf_max @var{float}
577 In CRF mode, prevents VBV from lowering quality beyond this point.
578 @item -qp @var{integer}
579 Constant quantization parameter rate control method.
580 @item -aq-mode @var{integer}
588 Variance AQ (complexity mask).
590 Auto-variance AQ (experimental).
592 @item -aq-strength @var{float}
593 AQ strength, reduces blocking and blurring in flat and textured areas.
594 @item -psy @var{integer}
595 Use psychovisual optimizations.
596 @item -psy-rd @var{string}
597 Strength of psychovisual optimization, in <psy-rd>:<psy-trellis> format.
598 @item -rc-lookahead @var{integer}
599 Number of frames to look ahead for frametype and ratecontrol.
600 @item -weightb @var{integer}
601 Weighted prediction for B-frames.
602 @item -weightp @var{integer}
603 Weighted prediction analysis method.
614 @item -ssim @var{integer}
615 Calculate and print SSIM stats.
616 @item -intra-refresh @var{integer}
617 Use Periodic Intra Refresh instead of IDR frames.
618 @item -bluray-compat @var{integer}
619 Configure the encoder to be compatible with the bluray standard.
620 It is a shorthand for setting "bluray-compat=1 force-cfr=1".
621 @item -b-bias @var{integer}
622 Influences how often B-frames are used.
623 @item -b-pyramid @var{integer}
624 Keep some B-frames as references.
631 Strictly hierarchical pyramid.
633 Non-strict (not Blu-ray compatible).
635 @item -mixed-refs @var{integer}
636 One reference per partition, as opposed to one reference per macroblock.
637 @item -8x8dct @var{integer}
638 High profile 8x8 transform.
639 @item -fast-pskip @var{integer}
640 @item -aud @var{integer}
641 Use access unit delimiters.
642 @item -mbtree @var{integer}
643 Use macroblock tree ratecontrol.
644 @item -deblock @var{string}
645 Loop filter parameters, in <alpha:beta> form.
646 @item -cplxblur @var{float}
647 Reduce fluctuations in QP (before curve compression).
648 @item -partitions @var{string}
649 A comma-separated list of partitions to consider, possible values: p8x8, p4x4, b8x8, i8x8, i4x4, none, all.
650 @item -direct-pred @var{integer}
651 Direct MV prediction mode
664 @item -slice-max-size @var{integer}
665 Limit the size of each slice in bytes.
666 @item -stats @var{string}
667 Filename for 2 pass stats.
668 @item -nal-hrd @var{integer}
669 Signal HRD information (requires vbv-bufsize; cbr not allowed in .mp4).
680 @item -x264-params @var{string}
681 Override the x264 configuration using a :-separated list of key=value parameters.
683 -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
687 Encoding avpresets for common usages are provided so they can be used with the
688 general presets system (e.g. passing the @code{-pre} option).
692 Apple ProRes encoder.
694 @subsection Private Options
697 @item profile @var{integer}
698 Select the ProRes profile to encode
707 @item quant_mat @var{integer}
708 Select quantization matrix.
717 If set to @var{auto}, the matrix matching the profile will be picked.
718 If not set, the matrix providing the highest quality, @var{default}, will be
721 @item bits_per_mb @var{integer}
722 How many bits to allot for coding one macroblock. Different profiles use
723 between 200 and 2400 bits per macroblock, the maximum is 8000.
725 @item mbs_per_slice @var{integer}
726 Number of macroblocks in each slice (1-8); the default value (8)
727 should be good in almost all situations.
729 @item vendor @var{string}
730 Override the 4-byte vendor ID.
731 A custom vendor ID like @var{apl0} would claim the stream was produced by
734 @item alpha_bits @var{integer}
735 Specify number of bits for alpha component.
736 Possible values are @var{0}, @var{8} and @var{16}.
737 Use @var{0} to disable alpha plane coding.
741 @subsection Speed considerations
743 In the default mode of operation the encoder has to honor frame constraints
744 (i.e. not produc frames with size bigger than requested) while still making
745 output picture as good as possible.
746 A frame containing a lot of small details is harder to compress and the encoder
747 would spend more time searching for appropriate quantizers for each slice.
749 Setting a higher @option{bits_per_mb} limit will improve the speed.
751 For the fastest encoding speed set the @option{qscale} parameter (4 is the
752 recommended value) and do not set a size constraint.
754 @c man end VIDEO ENCODERS