@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 @section libmp3lame LAME (Lame Ain't an MP3 Encoder) MP3 encoder wrapper. Requires the presence of the libmp3lame headers and library during configuration. You need to explicitly configure the build with @code{--enable-libmp3lame}. @subsection Option Mapping The following options are supported by the libmp3lame wrapper, the LAME-equivalent options follow the FFmpeg ones. @multitable @columnfractions .2 .2 @item FFmpeg @tab LAME @item b @tab b Set bitrate expressed in bits/s, LAME @code{bitrate} is expressed in kilobits/s. @item q @tab V Set quality setting for VBR. @item compression_level @tab q Set algorithm quality. Valid arguments are integers in the 0-9 range. @item reservoir @tab N.A. Enable use of bit reservoir. LAME has this enabled by default. @item joint_stereo @tab -m j Enable the encoder to use (on a frame by frame basis) either L/R stereo or mid/side stereo. @end multitable @section libopencore-amrnb OpenCORE Adaptive Multi-Rate Narrowband encoder. Requires the presence of the libopencore-amrnb headers and library during configuration. You need to explicitly configure the build with @code{--enable-libopencore-amrnb --enable-version3}. This is a mono-only encoder. Officially it only supports 8000Hz sample rate, but you can override it by setting @option{strict} to @samp{unofficial} or lower. @subsection Options @table @option @item b Set bitrate in bits per second. Only the following bitrates are supported, otherwise libavcodec will round to the nearest valid bitrate. @table @option @item 4750 @item 5150 @item 5900 @item 6700 @item 7400 @item 7950 @item 10200 @item 12200 @end table @item dtx Allow discontinuous transmission (generate comfort noise) when set to 1. The default value is 0 (disabled). @end table @section libtwolame TwoLAME MP2 encoder wrapper. Requires the presence of the libtwolame headers and library during configuration. You need to explicitly configure the build with @code{--enable-libtwolame}. @subsection Options Mapping The following options are supported by the libtwolame wrapper. The TwoLAME-equivalent options follow the FFmpeg ones and are in parentheses. @table @option @item b (b) Set bitrate in bits/s. Note that FFmpeg @code{b} option is expressed in bits/s, twolame @code{b} in kilobits/s. The default value is 128k. @item q (V) Set quality for experimental VBR support. Maximum value range is from -50 to 50, useful range is from -10 to 10. @item mode (mode) Set MPEG mode. Possible values: @table @samp @item auto Choose mode automatically based on the input. This is the default. @item stereo Stereo @item joint_stereo Joint stereo @item dual_channel Dual channel @item mono Mono @end table @item psymodel (psyc-mode) Set psychoacoustic model to use in encoding. The argument must be an integer between -1 and 4, inclusive. The higher the value, the better the quality. The default value is 3. @item energy_levels (energy) Enable energy levels extensions when set to 1. The default value is 0 (disabled). @item error_protection (protect) Enable CRC error protection when set to 1. The default value is 0 (disabled). @item copyright (copyright) Set MPEG audio copyright flag when set to 1. The default value is 0 (disabled). @item original (original) Set MPEG audio original flag when set to 1. The default value is 0 (disabled). @end table @section libvo-aacenc VisualOn AAC encoder. Requires the presence of the libvo-aacenc headers and library during configuration. You need to explicitly configure the build with @code{--enable-libvo-aacenc --enable-version3}. @subsection Options The VisualOn AAC encoder only support encoding AAC-LC and up to 2 channels. It is also CBR-only. It is considered to be worse than the native experimental FFmpeg AAC encoder. @table @option @item b Bitrate. @end table @section libvo-amrwbenc VisualOn Adaptive Multi-Rate Wideband encoder. Requires the presence of the libvo-amrwbenc headers and library during configuration. You need to explicitly configure the build with @code{--enable-libvo-amrwbenc --enable-version3}. This is a mono-only encoder. Officially it only supports 16000Hz sample rate, but you can override it by setting @option{strict} to @samp{unofficial} or lower. @subsection Options @table @option @item b Set bitrate in bits/s. Only the following bitrates are supported, otherwise libavcodec will round to the nearest valid bitrate. @table @samp @item 6600 @item 8850 @item 12650 @item 14250 @item 15850 @item 18250 @item 19850 @item 23050 @item 23850 @end table @item dtx Allow discontinuous transmission (generate comfort noise) when set to 1. The default value is 0 (disabled). @end table @section libwavpack A wrapper providing WavPack encoding through libwavpack. Only lossless mode using 32-bit integer samples is supported currently. The @option{compression_level} option can be used to control speed vs. compression tradeoff, with the values mapped to libwavpack as follows: @table @option @item 0 Fast mode - corresponding to the wavpack @option{-f} option. @item 1 Normal (default) settings. @item 2 High quality - corresponding to the wavpack @option{-h} option. @item 3 Very high quality - corresponding to the wavpack @option{-hh} option. @item 4-8 Same as 3, but with extra processing enabled - corresponding to the wavpack @option{-x} option. I.e. 4 is the same as @option{-x2} and 8 is the same as @option{-x6}. @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 libtheora Theora format supported through libtheora. Requires the presence of the libtheora headers and library during configuration. You need to explicitly configure the build with @code{--enable-libtheora}. @subsection Options The following global options are mapped to internal libtheora options which affect the quality and the bitrate of the encoded stream. @table @option @item b Set the video bitrate, only works if the @code{qscale} flag in @option{flags} is not enabled. @item flags Used to enable constant quality mode encoding through the @option{qscale} flag, and to enable the @code{pass1} and @code{pass2} modes. @item g Set the GOP size. @item global_quality Set the global quality in lambda units, only works if the @code{qscale} flag in @option{flags} is enabled. The value is clipped in the [0 - 10*@code{FF_QP2LAMBDA}] range, and then multiplied for 6.3 to get a value in the native libtheora range [0-63]. A higher value corresponds to a higher quality. For example, to set maximum constant quality encoding with @command{ffmpeg}: @example ffmpeg -i INPUT -flags:v qscale -global_quality:v "10*QP2LAMBDA" -codec:v libtheora OUTPUT.ogg @end example @end table @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 max-intra-rate @code{VP8E_SET_MAX_INTRA_BITRATE_PCT} @item force_key_frames @code{VPX_EFLAG_FORCE_KF} @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 x264 H.264/MPEG-4 AVC encoder wrapper. Requires the presence of the libx264 headers and library during configuration. You need to explicitly configure the build with @code{--enable-libx264}. x264 supports an impressive number of features, including 8x8 and 4x4 adaptive spatial transform, adaptive B-frame placement, CAVLC/CABAC entropy coding, interlacing (MBAFF), lossless mode, psy optimizations for detail retention (adaptive quantization, psy-RD, psy-trellis). The FFmpeg wrapper provides a mapping for most of them using global options that match those of the encoders and provides private options for the unique encoder options. Additionally an expert override is provided to directly pass a list of key=value tuples as accepted by x264_param_parse. @subsection Option Mapping The following options are supported by the x264 wrapper, the x264-equivalent options follow the FFmpeg ones. @multitable @columnfractions .2 .2 @item b @tab bitrate FFmpeg @code{b} option is expressed in bits/s, x264 @code{bitrate} in kilobits/s. @item bf @tab bframes Maximum number of B-frames. @item g @tab keyint Maximum GOP size. @item qmin @tab qpmin @item qmax @tab qpmax @item qdiff @tab qpstep @item qblur @tab qblur @item qcomp @tab qcomp @item refs @tab ref @item sc_threshold @tab scenecut @item trellis @tab trellis @item nr @tab nr Noise reduction. @item me_range @tab merange @item me_method @tab me @item subq @tab subme @item b_strategy @tab b-adapt @item keyint_min @tab keyint-min @item coder @tab cabac Set coder to @code{ac} to use CABAC. @item cmp @tab chroma-me Set to @code{chroma} to use chroma motion estimation. @item threads @tab threads @item thread_type @tab sliced_threads Set to @code{slice} to use sliced threading instead of frame threading. @item flags -cgop @tab open-gop Set @code{-cgop} to use recovery points to close GOPs. @item rc_init_occupancy @tab vbv-init Initial buffer occupancy. @end multitable @subsection Private Options @table @option @item -preset @var{string} Set the encoding preset (cf. x264 --fullhelp). @item -tune @var{string} Tune the encoding params (cf. x264 --fullhelp). @item -profile @var{string} Set profile restrictions (cf. x264 --fullhelp). @item -fastfirstpass @var{integer} Use fast settings when encoding first pass. @item -crf @var{float} Select the quality for constant quality mode. @item -crf_max @var{float} In CRF mode, prevents VBV from lowering quality beyond this point. @item -qp @var{integer} Constant quantization parameter rate control method. @item -aq-mode @var{integer} AQ method Possible values: @table @samp @item none @item variance Variance AQ (complexity mask). @item autovariance Auto-variance AQ (experimental). @end table @item -aq-strength @var{float} AQ strength, reduces blocking and blurring in flat and textured areas. @item -psy @var{integer} Use psychovisual optimizations. @item -psy-rd @var{string} Strength of psychovisual optimization, in <psy-rd>:<psy-trellis> format. @item -rc-lookahead @var{integer} Number of frames to look ahead for frametype and ratecontrol. @item -weightb @var{integer} Weighted prediction for B-frames. @item -weightp @var{integer} Weighted prediction analysis method. Possible values: @table @samp @item none @item simple @item smart @end table @item -ssim @var{integer} Calculate and print SSIM stats. @item -intra-refresh @var{integer} Use Periodic Intra Refresh instead of IDR frames. @item -b-bias @var{integer} Influences how often B-frames are used. @item -b-pyramid @var{integer} Keep some B-frames as references. Possible values: @table @samp @item none @item strict Strictly hierarchical pyramid. @item normal Non-strict (not Blu-ray compatible). @end table @item -mixed-refs @var{integer} One reference per partition, as opposed to one reference per macroblock. @item -8x8dct @var{integer} High profile 8x8 transform. @item -fast-pskip @var{integer} @item -aud @var{integer} Use access unit delimiters. @item -mbtree @var{integer} Use macroblock tree ratecontrol. @item -deblock @var{string} Loop filter parameters, in <alpha:beta> form. @item -cplxblur @var{float} Reduce fluctuations in QP (before curve compression). @item -partitions @var{string} A comma-separated list of partitions to consider, possible values: p8x8, p4x4, b8x8, i8x8, i4x4, none, all. @item -direct-pred @var{integer} Direct MV prediction mode Possible values: @table @samp @item none @item spatial @item temporal @item auto @end table @item -slice-max-size @var{integer} Limit the size of each slice in bytes. @item -stats @var{string} Filename for 2 pass stats. @item -nal-hrd @var{integer} Signal HRD information (requires vbv-bufsize; cbr not allowed in .mp4). Possible values: @table @samp @item none @item vbr @item cbr @end table @item x264opts @var{options} Allow to set any x264 option, see @code{x264 --fullhelp} for a list. @var{options} is a list of @var{key}=@var{value} couples separated by ":". In @var{filter} and @var{psy-rd} options that use ":" as a separator themselves, use "," instead. They accept it as well since long ago but this is kept undocumented for some reason. 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} @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 @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). @section png PNG image encoder. @subsection Private options @table @option @item dpi @var{integer} Set physical density of pixels, in dots per inch, unset by default @item dpm @var{integer} Set physical density of pixels, in dots per meter, unset by default @end table @section ProRes Apple ProRes encoder. FFmpeg contains 2 ProRes encoders, the prores-aw and prores-ks encoder. The used encoder can be choosen with the @code{-vcodec} option. @subsection Private Options for prores-ks @table @option @item profile @var{integer} Select the ProRes profile to encode @table @samp @item proxy @item lt @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. @c man end VIDEO ENCODERS