mirror of https://github.com/FFmpeg/FFmpeg.git
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
1458 lines
38 KiB
1458 lines
38 KiB
@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 libopus |
|
|
|
libopus Opus Interactive Audio Codec encoder wrapper. |
|
|
|
Requires the presence of the libopus headers and library during |
|
configuration. You need to explicitly configure the build with |
|
@code{--enable-libopus}. |
|
|
|
@subsection Option Mapping |
|
|
|
Most libopus options are modeled after the @command{opusenc} utility from |
|
opus-tools. The following is an option mapping chart describing options |
|
supported by the libopus wrapper, and their @command{opusenc}-equivalent |
|
in parentheses. |
|
|
|
@table @option |
|
|
|
@item b (@emph{bitrate}) |
|
Set the bit rate in bits/s. FFmpeg's @option{b} option is |
|
expressed in bits/s, while @command{opusenc}'s @option{bitrate} in |
|
kilobits/s. |
|
|
|
@item vbr (@emph{vbr}, @emph{hard-cbr}, and @emph{cvbr}) |
|
Set VBR mode. The FFmpeg @option{vbr} option has the following |
|
valid arguments, with the their @command{opusenc} equivalent options |
|
in parentheses: |
|
|
|
@table @samp |
|
@item off (@emph{hard-cbr}) |
|
Use constant bit rate encoding. |
|
|
|
@item on (@emph{vbr}) |
|
Use variable bit rate encoding (the default). |
|
|
|
@item constrained (@emph{cvbr}) |
|
Use constrained variable bit rate encoding. |
|
@end table |
|
|
|
@item compression_level (@emph{comp}) |
|
Set encoding algorithm complexity. Valid options are integers in |
|
the 0-10 range. 0 gives the fastest encodes but lower quality, while 10 |
|
gives the highest quality but slowest encoding. The default is 10. |
|
|
|
@item frame_duration (@emph{framesize}) |
|
Set maximum frame size, or duration of a frame in milliseconds. The |
|
argument must be exactly the following: 2.5, 5, 10, 20, 40, 60. Smaller |
|
frame sizes achieve lower latency but less quality at a given bitrate. |
|
Sizes greater than 20ms are only interesting at fairly low bitrates. |
|
The default of FFmpeg is 10ms, but is 20ms in @command{opusenc}. |
|
|
|
@item packet_loss (@emph{expect-loss}) |
|
Set expected packet loss percentage. The default is 0. |
|
|
|
@item application (N.A.) |
|
Set intended application type. Valid options are listed below: |
|
|
|
@table @samp |
|
@item voip |
|
Favor improved speech intelligibility. |
|
@item audio |
|
Favor faithfulness to the input (the default). |
|
@item lowdelay |
|
Restrict to only the lowest delay modes. |
|
@end table |
|
|
|
@item cutoff (N.A.) |
|
Set cutoff bandwidth in Hz. The argument must be exactly one of the |
|
following: 4000, 6000, 8000, 12000, or 20000, corresponding to |
|
narrowband, mediumband, wideband, super wideband, and fullband |
|
respectively. The default is 0 (cutoff 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. |
|
|
|
This encoder requires the presence of the libx264 headers and library |
|
during configuration. You need to explicitly configure the build with |
|
@code{--enable-libx264}. |
|
|
|
libx264 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). |
|
|
|
Many libx264 encoder options are mapped to FFmpeg global codec |
|
options, while unique encoder options are provided through private |
|
options. Additionally the @option{x264opts} and @option{x264-params} |
|
private options allows to pass a list of key=value tuples as accepted |
|
by the libx264 @code{x264_param_parse} function. |
|
|
|
The x264 project website is at |
|
@url{http://www.videolan.org/developers/x264.html}. |
|
|
|
@subsection Options |
|
|
|
The following options are supported by the libx264 wrapper. The |
|
@command{x264}-equivalent options or values are listed in parentheses |
|
for easy migration. |
|
|
|
To reduce the duplication of documentation, only the private options |
|
and some others requiring special attention are documented here. For |
|
the documentation of the undocumented generic options, see |
|
@ref{codec-options,,the Codec Options chapter}. |
|
|
|
To get a more accurate and extensive documentation of the libx264 |
|
options, invoke the command @command{x264 --full-help} or consult |
|
the libx264 documentation. |
|
|
|
@table @option |
|
@item b (@emph{bitrate}) |
|
Set bitrate in bits/s. Note that FFmpeg's @option{b} option is |
|
expressed in bits/s, while @command{x264}'s @option{bitrate} is in |
|
kilobits/s. |
|
|
|
@item bf (@emph{bframes}) |
|
|
|
@item g (@emph{keyint}) |
|
|
|
@item qmax (@emph{qpmax}) |
|
|
|
@item qmin (@emph{qpmin}) |
|
|
|
@item qdiff (@emph{qpstep}) |
|
|
|
@item qblur (@emph{qblur}) |
|
|
|
@item qcomp (@emph{qcomp}) |
|
|
|
@item refs (@emph{ref}) |
|
|
|
@item sc_threshold (@emph{scenecut}) |
|
|
|
@item trellis (@emph{trellis}) |
|
|
|
@item nr (@emph{nr}) |
|
|
|
@item me_range (@emph{merange}) |
|
|
|
@item me_method (@emph{me}) |
|
Set motion estimation method. Possible values in the decreasing order |
|
of speed: |
|
|
|
@table @samp |
|
@item dia (@emph{dia}) |
|
@item epzs (@emph{dia}) |
|
Diamond search with radius 1 (fastest). @samp{epzs} is an alias for |
|
@samp{dia}. |
|
@item hex (@emph{hex}) |
|
Hexagonal search with radius 2. |
|
@item umh (@emph{umh}) |
|
Uneven multi-hexagon search. |
|
@item esa (@emph{esa}) |
|
Exhaustive search. |
|
@item tesa (@emph{tesa}) |
|
Hadamard exhaustive search (slowest). |
|
@end table |
|
|
|
@item subq (@emph{subme}) |
|
|
|
@item b_strategy (@emph{b-adapt}) |
|
|
|
@item keyint_min (@emph{min-keyint}) |
|
|
|
@item coder |
|
Set entropy encoder. Possible values: |
|
|
|
@table @samp |
|
@item ac |
|
Enable CABAC. |
|
|
|
@item vlc |
|
Enable CAVLC and disable CABAC. It generates the same effect as |
|
@command{x264}'s @option{--no-cabac} option. |
|
@end table |
|
|
|
@item cmp |
|
Set full pixel motion estimation comparation algorithm. Possible values: |
|
|
|
@table @samp |
|
@item chroma |
|
Enable chroma in motion estimation. |
|
|
|
@item sad |
|
Ignore chroma in motion estimation. It generates the same effect as |
|
@command{x264}'s @option{--no-chroma-me} option. |
|
@end table |
|
|
|
@item threads (@emph{threads}) |
|
|
|
@item thread_type |
|
Set multithreading technique. Possible values: |
|
|
|
@table @samp |
|
@item slice |
|
Slice-based multithreading. It generates the same effect as |
|
@command{x264}'s @option{--sliced-threads} option. |
|
@item frame |
|
Frame-based multithreading. |
|
@end table |
|
|
|
@item flags |
|
Set encoding flags. It can be used to disable closed GOP and enable |
|
open GOP by setting it to @code{-cgop}. The result is similar to |
|
the behavior of @command{x264}'s @option{--open-gop} option. |
|
|
|
@item rc_init_occupancy (@emph{vbv-init}) |
|
|
|
@item preset (@emph{preset}) |
|
Set the encoding preset. |
|
|
|
@item tune (@emph{tune}) |
|
Set tuning of the encoding params. |
|
|
|
@item profile (@emph{profile}) |
|
Set profile restrictions. |
|
|
|
@item fastfirstpass |
|
Enable fast settings when encoding first pass, when set to 1. When set |
|
to 0, it has the same effect of @command{x264}'s |
|
@option{--slow-firstpass} option. |
|
|
|
@item crf (@emph{crf}) |
|
Set the quality for constant quality mode. |
|
|
|
@item crf_max (@emph{crf-max}) |
|
In CRF mode, prevents VBV from lowering quality beyond this point. |
|
|
|
@item qp (@emph{qp}) |
|
Set constant quantization rate control method parameter. |
|
|
|
@item aq-mode (@emph{aq-mode}) |
|
Set AQ method. Possible values: |
|
|
|
@table @samp |
|
@item none (@emph{0}) |
|
Disabled. |
|
|
|
@item variance (@emph{1}) |
|
Variance AQ (complexity mask). |
|
|
|
@item autovariance (@emph{2}) |
|
Auto-variance AQ (experimental). |
|
@end table |
|
|
|
@item aq-strength (@emph{aq-strength}) |
|
Set AQ strength, reduce blocking and blurring in flat and textured areas. |
|
|
|
@item psy |
|
Use psychovisual optimizations when set to 1. When set to 0, it has the |
|
same effect as @command{x264}'s @option{--no-psy} option. |
|
|
|
@item psy-rd (@emph{psy-rd}) |
|
Set strength of psychovisual optimization, in |
|
@var{psy-rd}:@var{psy-trellis} format. |
|
|
|
@item rc-lookahead (@emph{rc-lookahead}) |
|
Set number of frames to look ahead for frametype and ratecontrol. |
|
|
|
@item weightb |
|
Enable weighted prediction for B-frames when set to 1. When set to 0, |
|
it has the same effect as @command{x264}'s @option{--no-weightb} option. |
|
|
|
@item weightp (@emph{weightp}) |
|
Set weighted prediction method for P-frames. Possible values: |
|
|
|
@table @samp |
|
@item none (@emph{0}) |
|
Disabled |
|
@item simple (@emph{1}) |
|
Enable only weighted refs |
|
@item smart (@emph{2}) |
|
Enable both weighted refs and duplicates |
|
@end table |
|
|
|
@item ssim (@emph{ssim}) |
|
Enable calculation and printing SSIM stats after the encoding. |
|
|
|
@item intra-refresh (@emph{intra-refresh}) |
|
Enable the use of Periodic Intra Refresh instead of IDR frames when set |
|
to 1. |
|
|
|
@item b-bias (@emph{b-bias}) |
|
Set the influence on how often B-frames are used. |
|
|
|
@item b-pyramid (@emph{b-pyramid}) |
|
Set method for keeping of some B-frames as references. Possible values: |
|
|
|
@table @samp |
|
@item none (@emph{none}) |
|
Disabled. |
|
@item strict (@emph{strict}) |
|
Strictly hierarchical pyramid. |
|
@item normal (@emph{normal}) |
|
Non-strict (not Blu-ray compatible). |
|
@end table |
|
|
|
@item mixed-refs |
|
Enable the use of one reference per partition, as opposed to one |
|
reference per macroblock when set to 1. When set to 0, it has the |
|
same effect as @command{x264}'s @option{--no-mixed-refs} option. |
|
|
|
@item 8x8dct |
|
Enable adaptive spatial transform (high profile 8x8 transform) |
|
when set to 1. When set to 0, it has the same effect as |
|
@command{x264}'s @option{--no-8x8dct} option. |
|
|
|
@item fast-pskip |
|
Enable early SKIP detection on P-frames when set to 1. When set |
|
to 0, it has the same effect as @command{x264}'s |
|
@option{--no-fast-pskip} option. |
|
|
|
@item aud (@emph{aud}) |
|
Enable use of access unit delimiters when set to 1. |
|
|
|
@item mbtree |
|
Enable use macroblock tree ratecontrol when set to 1. When set |
|
to 0, it has the same effect as @command{x264}'s |
|
@option{--no-mbtree} option. |
|
|
|
@item deblock (@emph{deblock}) |
|
Set loop filter parameters, in @var{alpha}:@var{beta} form. |
|
|
|
@item cplxblur (@emph{cplxblur}) |
|
Set fluctuations reduction in QP (before curve compression). |
|
|
|
@item partitions (@emph{partitions}) |
|
Set partitions to consider as a comma-separated list of. Possible |
|
values in the list: |
|
|
|
@table @samp |
|
@item p8x8 |
|
8x8 P-frame partition. |
|
@item p4x4 |
|
4x4 P-frame partition. |
|
@item b8x8 |
|
4x4 B-frame partition. |
|
@item i8x8 |
|
8x8 I-frame partition. |
|
@item i4x4 |
|
4x4 I-frame partition. |
|
(Enabling @samp{p4x4} requires @samp{p8x8} to be enabled. Enabling |
|
@samp{i8x8} requires adaptive spatial transform (@option{8x8dct} |
|
option) to be enabled.) |
|
@item none (@emph{none}) |
|
Do not consider any partitions. |
|
@item all (@emph{all}) |
|
Consider every partition. |
|
@end table |
|
|
|
@item direct-pred (@emph{direct}) |
|
Set direct MV prediction mode. Possible values: |
|
|
|
@table @samp |
|
@item none (@emph{none}) |
|
Disable MV prediction. |
|
@item spatial (@emph{spatial}) |
|
Enable spatial predicting. |
|
@item temporal (@emph{temporal}) |
|
Enable temporal predicting. |
|
@item auto (@emph{auto}) |
|
Automatically decided. |
|
@end table |
|
|
|
@item slice-max-size (@emph{slice-max-size}) |
|
Set the limit of the size of each slice in bytes. If not specified |
|
but RTP payload size (@option{ps}) is specified, that is used. |
|
|
|
@item stats (@emph{stats}) |
|
Set the file name for multi-pass stats. |
|
|
|
@item nal-hrd (@emph{nal-hrd}) |
|
Set signal HRD information (requires @option{vbv-bufsize} to be set). |
|
Possible values: |
|
|
|
@table @samp |
|
@item none (@emph{none}) |
|
Disable HRD information signaling. |
|
@item vbr (@emph{vbr}) |
|
Variable bit rate. |
|
@item cbr (@emph{cbr}) |
|
Constant bit rate (not allowed in MP4 container). |
|
@end table |
|
|
|
@item x264opts (N.A.) |
|
Set any x264 option, see @command{x264 --fullhelp} for a list. |
|
|
|
Argument 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 |
|
|
|
@item x264-params (N.A.) |
|
Override the x264 configuration using a :-separated list of key=value |
|
parameters. |
|
|
|
This option is functionally the same as the @option{x264opts}, but is |
|
duplicated for compability with the Libav fork. |
|
|
|
For example to specify libx264 encoding options with @command{ffmpeg}: |
|
@example |
|
ffmpeg -i INPUT -c:v libx264 -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 OUTPUT |
|
@end example |
|
@end table |
|
|
|
Encoding ffpresets for common usages are provided so they can be used with the |
|
general presets system (e.g. passing the @option{pre} option). |
|
|
|
@section libxvid |
|
|
|
Xvid MPEG-4 Part 2 encoder wrapper. |
|
|
|
This encoder requires the presence of the libxvidcore headers and library |
|
during configuration. You need to explicitly configure the build with |
|
@code{--enable-libxvid --enable-gpl}. |
|
|
|
The native @code{mpeg4} encoder supports the MPEG-4 Part 2 format, so |
|
users can encode to this format without this library. |
|
|
|
@subsection Options |
|
|
|
The following options are supported by the libxvid wrapper. Some of |
|
the following options are listed but are not documented, and |
|
correspond to shared codec options. See @ref{codec-options,,the Codec |
|
Options chapter} for their documentation. The other shared options |
|
which are not listed have no effect for the libxvid encoder. |
|
|
|
@table @option |
|
@item b |
|
|
|
@item g |
|
|
|
@item qmin |
|
|
|
@item qmax |
|
|
|
@item mpeg_quant |
|
|
|
@item threads |
|
|
|
@item bf |
|
|
|
@item b_qfactor |
|
|
|
@item b_qoffset |
|
|
|
@item flags |
|
Set specific encoding flags. Possible values: |
|
|
|
@table @samp |
|
|
|
@item mv4 |
|
Use four motion vector by macroblock. |
|
|
|
@item aic |
|
Enable high quality AC prediction. |
|
|
|
@item gray |
|
Only encode grayscale. |
|
|
|
@item gmc |
|
Enable the use of global motion compensation (GMC). |
|
|
|
@item qpel |
|
Enable quarter-pixel motion compensation. |
|
|
|
@item cgop |
|
Enable closed GOP. |
|
|
|
@item global_header |
|
Place global headers in extradata instead of every keyframe. |
|
|
|
@end table |
|
|
|
@item trellis |
|
|
|
@item me_method |
|
Set motion estimation method. Possible values in decreasing order of |
|
speed and increasing order of quality: |
|
|
|
@table @samp |
|
@item zero |
|
Use no motion estimation (default). |
|
|
|
@item phods |
|
@item x1 |
|
@item log |
|
Enable advanced diamond zonal search for 16x16 blocks and half-pixel |
|
refinement for 16x16 blocks. @samp{x1} and @samp{log} are aliases for |
|
@samp{phods}. |
|
|
|
@item epzs |
|
Enable all of the things described above, plus advanced diamond zonal |
|
search for 8x8 blocks, half-pixel refinement for 8x8 blocks, and motion |
|
estimation on chroma planes. |
|
|
|
@item full |
|
Enable all of the things described above, plus extended 16x16 and 8x8 |
|
blocks search. |
|
@end table |
|
|
|
@item mbd |
|
Set macroblock decision algorithm. Possible values in the increasing |
|
order of quality: |
|
|
|
@table @samp |
|
@item simple |
|
Use macroblock comparing function algorithm (default). |
|
|
|
@item bits |
|
Enable rate distortion-based half pixel and quarter pixel refinement for |
|
16x16 blocks. |
|
|
|
@item rd |
|
Enable all of the things described above, plus rate distortion-based |
|
half pixel and quarter pixel refinement for 8x8 blocks, and rate |
|
distortion-based search using square pattern. |
|
@end table |
|
|
|
@item lumi_aq |
|
Enable lumi masking adaptive quantization when set to 1. Default is 0 |
|
(disabled). |
|
|
|
@item variance_aq |
|
Enable variance adaptive quantization when set to 1. Default is 0 |
|
(disabled). |
|
|
|
When combined with @option{lumi_aq}, the resulting quality will not |
|
be better than any of the two specified individually. In other |
|
words, the resulting quality will be the worse one of the two |
|
effects. |
|
|
|
@item ssim |
|
Set structural similarity (SSIM) displaying method. Possible values: |
|
|
|
@table @samp |
|
@item off |
|
Disable displaying of SSIM information. |
|
|
|
@item avg |
|
Output average SSIM at the end of encoding to stdout. The format of |
|
showing the average SSIM is: |
|
|
|
@example |
|
Average SSIM: %f |
|
@end example |
|
|
|
For users who are not familiar with C, %f means a float number, or |
|
a decimal (e.g. 0.939232). |
|
|
|
@item frame |
|
Output both per-frame SSIM data during encoding and average SSIM at |
|
the end of encoding to stdout. The format of per-frame information |
|
is: |
|
|
|
@example |
|
SSIM: avg: %1.3f min: %1.3f max: %1.3f |
|
@end example |
|
|
|
For users who are not familiar with C, %1.3f means a float number |
|
rounded to 3 digits after the dot (e.g. 0.932). |
|
|
|
@end table |
|
|
|
@item ssim_acc |
|
Set SSIM accuracy. Valid options are integers within the range of |
|
0-4, while 0 gives the most accurate result and 4 computes the |
|
fastest. |
|
|
|
@end table |
|
|
|
@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
|
|
|