librempeg/doc/decoders.texi

@chapter Decoders
@c man begin DECODERS

Decoders are configured elements in FFmpeg which allow the decoding of
multimedia streams.

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

You can disable all the decoders with the configure option
@code{--disable-decoders} and selectively enable / disable single decoders
with the options @code{--enable-decoder=@var{DECODER}} /
@code{--disable-decoder=@var{DECODER}}.

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

@c man end DECODERS

@chapter Video Decoders
@c man begin VIDEO DECODERS

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

@section av1

AOMedia Video 1 (AV1) decoder.

@subsection Options

@table @option

@item operating_point
Select an operating point of a scalable AV1 bitstream (0 - 31). Default is 0.

@end table

@section hevc
HEVC (AKA ITU-T H.265 or ISO/IEC 23008-2) decoder.

The decoder supports MV-HEVC multiview streams with at most two views. Views to
be output are selected by supplying a list of view IDs to the decoder (the
@option{view_ids} option). This option may be set either statically before
decoder init, or from the @code{get_format()} callback - useful for the case
when the view count or IDs change dynamically during decoding.

Only the base layer is decoded by default.

Note that if you are using the @code{ffmpeg} CLI tool, you should be using view
specifiers as documented in its manual, rather than the options documented here.

@subsection Options

@table @option

@item view_ids (MV-HEVC)
Specify a list of view IDs that should be output. This option can also be set to
a single '-1', which will cause all views defined in the VPS to be decoded and
output.

@item view_ids_available (MV-HEVC)
This option may be read by the caller to retrieve an array of view IDs available
in the active VPS. The array is empty for single-layer video.

The value of this option is guaranteed to be accurate when read from the
@code{get_format()} callback. It may also be set at other times (e.g. after
opening the decoder), but the value is informational only and may be incorrect
(e.g. when the stream contains multiple distinct VPS NALUs).

@item view_pos_available (MV-HEVC)
This option may be read by the caller to retrieve an array of view positions
(left, right, or unspecified) available in the active VPS, as
@code{AVStereo3DView} values. When the array is available, its elements apply to
the corresponding elements of @option{view_ids_available}, i.e.
@code{view_pos_available[i]} contains the position of view with ID
@code{view_ids_available[i]}.

Same validity restrictions as for @option{view_ids_available} apply to
this option.

@end table

@section rawvideo

Raw video decoder.

This decoder decodes rawvideo streams.

@subsection Options

@table @option
@item top @var{top_field_first}
Specify the assumed field type of the input video.
@table @option
@item -1
the video is assumed to be progressive (default)
@item 0
bottom-field-first is assumed
@item 1
top-field-first is assumed
@end table

@end table

@section libdav1d

dav1d AV1 decoder.

libdav1d allows libavcodec to decode the AOMedia Video 1 (AV1) codec.
Requires the presence of the libdav1d headers and library during configuration.
You need to explicitly configure the build with @code{--enable-libdav1d}.

@subsection Options

The following options are supported by the libdav1d wrapper.

@table @option

@item framethreads
Set amount of frame threads to use during decoding. The default value is 0 (autodetect).
This option is deprecated for libdav1d >= 1.0 and will be removed in the future. Use the
option @code{max_frame_delay} and the global option @code{threads} instead.

@item tilethreads
Set amount of tile threads to use during decoding. The default value is 0 (autodetect).
This option is deprecated for libdav1d >= 1.0 and will be removed in the future. Use the
global option @code{threads} instead.

@item max_frame_delay
Set max amount of frames the decoder may buffer internally. The default value is 0
(autodetect).

@item filmgrain
Apply film grain to the decoded video if present in the bitstream. Defaults to the
internal default of the library.
This option is deprecated and will be removed in the future. See the global option
@code{export_side_data} to export Film Grain parameters instead of applying it.

@item oppoint
Select an operating point of a scalable AV1 bitstream (0 - 31). Defaults to the
internal default of the library.

@item alllayers
Output all spatial layers of a scalable AV1 bitstream. The default value is false.

@end table

@section libdavs2

AVS2-P2/IEEE1857.4 video decoder wrapper.

This decoder allows libavcodec to decode AVS2 streams with davs2 library.

@c man end VIDEO DECODERS

@section libuavs3d

AVS3-P2/IEEE1857.10 video decoder.

libuavs3d allows libavcodec to decode AVS3 streams.
Requires the presence of the libuavs3d headers and library during configuration.
You need to explicitly configure the build with @code{--enable-libuavs3d}.

@subsection Options

The following option is supported by the libuavs3d wrapper.

@table @option

@item frame_threads
Set amount of frame threads to use during decoding. The default value is 0 (autodetect).

@end table

@section libxevd

eXtra-fast Essential Video Decoder (XEVD) MPEG-5 EVC decoder wrapper.

This decoder requires the presence of the libxevd headers and library
during configuration. You need to explicitly configure the build with
@option{--enable-libxevd}.

The xevd project website is at @url{https://github.com/mpeg5/xevd}.

@subsection Options

The following options are supported by the libxevd wrapper.
The xevd-equivalent options or values are listed in parentheses for easy migration.

To get a more accurate and extensive documentation of the libxevd options,
invoke the command  @code{xevd_app --help} or consult the libxevd documentation.

@table @option
@item threads (@emph{threads})
Force to use a specific number of threads

@end table

@section QSV Decoders

The family of Intel QuickSync Video decoders (VC1, MPEG-2, H.264, HEVC,
JPEG/MJPEG, VP8, VP9, AV1).

@subsection Common Options

The following options are supported by all qsv decoders.

@table @option

@item @var{async_depth}
Internal parallelization depth, the higher the value the higher the latency.

@item @var{gpu_copy}
A GPU-accelerated copy between video and system memory
@table @samp
@item default
@item on
@item off
@end table

@end table

@subsection HEVC Options
Extra options for hevc_qsv.

@table @option

@item @var{load_plugin}
A user plugin to load in an internal session
@table @samp
@item none
@item hevc_sw
@item hevc_hw
@end table

@item @var{load_plugins}
A :-separate list of hexadecimal plugin UIDs to load in an internal session

@end table

@section v210

Uncompressed 4:2:2 10-bit decoder.

@subsection Options

@table @option

@item custom_stride
Set the line size of the v210 data in bytes. The default value is 0
(autodetect). You can use the special -1 value for a strideless v210 as seen in
BOXX files.

@end table

@c man end VIDEO DECODERS

@chapter Audio Decoders
@c man begin AUDIO DECODERS

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

@section ac3

AC-3 audio decoder.

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

@subsection AC-3 Decoder Options

@table @option

@item -drc_scale @var{value}
Dynamic Range Scale Factor. The factor to apply to dynamic range values
from the AC-3 stream. This factor is applied exponentially. The default value is 1.
There are 3 notable scale factor ranges:
@table @option
@item drc_scale == 0
DRC disabled. Produces full range audio.
@item 0 < drc_scale <= 1
DRC enabled.  Applies a fraction of the stream DRC value.
Audio reproduction is between full range and full compression.
@item drc_scale > 1
DRC enabled. Applies drc_scale asymmetrically.
Loud sounds are fully compressed.  Soft sounds are enhanced.
@end table

@end table

@section flac

FLAC audio decoder.

This decoder aims to implement the complete FLAC specification from Xiph.

@subsection FLAC Decoder options

@table @option

@item -use_buggy_lpc
The lavc FLAC encoder used to produce buggy streams with high lpc values
(like the default value). This option makes it possible to decode such streams
correctly by using lavc's old buggy lpc logic for decoding.

@end table

@section ffwavesynth

Internal wave synthesizer.

This decoder generates wave patterns according to predefined sequences. Its
use is purely internal and the format of the data it accepts is not publicly
documented.

@section libcelt

libcelt decoder wrapper.

libcelt allows libavcodec to decode the Xiph CELT ultra-low delay audio codec.
Requires the presence of the libcelt headers and library during configuration.
You need to explicitly configure the build with @code{--enable-libcelt}.

@section libgsm

libgsm decoder wrapper.

libgsm allows libavcodec to decode the GSM full rate audio codec. Requires
the presence of the libgsm headers and library during configuration. You need
to explicitly configure the build with @code{--enable-libgsm}.

This decoder supports both the ordinary GSM and the Microsoft variant.

@section libopencore-amrnb

libopencore-amrnb decoder wrapper.

libopencore-amrnb allows libavcodec to decode the Adaptive Multi-Rate
Narrowband audio codec. Using it requires the presence of the
libopencore-amrnb headers and library during configuration. You need to
explicitly configure the build with @code{--enable-libopencore-amrnb}.

An FFmpeg native decoder for AMR-NB exists, so users can decode AMR-NB
without this library.

@section libopencore-amrwb

libopencore-amrwb decoder wrapper.

libopencore-amrwb allows libavcodec to decode the Adaptive Multi-Rate
Wideband audio codec. Using it requires the presence of the
libopencore-amrwb headers and library during configuration. You need to
explicitly configure the build with @code{--enable-libopencore-amrwb}.

An FFmpeg native decoder for AMR-WB exists, so users can decode AMR-WB
without this library.

@section libopus

libopus decoder wrapper.

libopus allows libavcodec to decode the Opus Interactive Audio Codec.
Requires the presence of the libopus headers and library during
configuration. You need to explicitly configure the build with
@code{--enable-libopus}.

An FFmpeg native decoder for Opus exists, so users can decode Opus
without this library.

@c man end AUDIO DECODERS

@chapter Subtitles Decoders
@c man begin SUBTILES DECODERS

@section libaribb24

ARIB STD-B24 caption decoder.

Implements profiles A and C of the ARIB STD-B24 standard.

@subsection libaribb24 Decoder Options

@table @option

@item -aribb24-base-path @var{path}
Sets the base path for the libaribb24 library. This is utilized for reading of
configuration files (for custom unicode conversions), and for dumping of
non-text symbols as images under that location.

Unset by default.

@item -aribb24-skip-ruby-text @var{boolean}
Tells the decoder wrapper to skip text blocks that contain half-height ruby
text.

Enabled by default.

@end table

@section libaribcaption

Yet another ARIB STD-B24 caption decoder using external @dfn{libaribcaption}
library.

Implements profiles A and C of the Japanse ARIB STD-B24 standard,
Brazilian ABNT NBR 15606-1, and Philippines version of ISDB-T.

Requires the presence of the libaribcaption headers and library
(@url{https://github.com/xqq/libaribcaption}) during configuration.
You need to explicitly configure the build with @code{--enable-libaribcaption}.
If both @dfn{libaribb24} and @dfn{libaribcaption} are enabled, @dfn{libaribcaption}
decoder precedes.

@subsection libaribcaption Decoder Options

@table @option

@item -sub_type @var{subtitle_type}
Specifies the format of the decoded subtitles.

@table @samp
@item bitmap
Graphical image.
@item ass
ASS formatted text.
@item text
Simple text based output without formatting.
@end table

The default is @dfn{ass} as same as @dfn{libaribb24} decoder.
Some present players (e.g., @dfn{mpv}) expect ASS format for ARIB caption.

@item -caption_encoding @var{encoding_scheme}
Specifies the encoding scheme of input subtitle text.

@table @samp
@item auto
Automatically detect text encoding (default).
@item jis
8bit-char JIS encoding defined in ARIB STD B24.
This encoding used in Japan for ISDB captions.
@item utf8
UTF-8 encoding defined in ARIB STD B24.
This encoding is used in Philippines for ISDB-T captions.
@item latin
Latin character encoding defined in ABNT NBR 15606-1.
This encoding is used in South America for SBTVD / ISDB-Tb captions.
@end table

@item -font @var{font_name[,font_name2,...]}
Specify comma-separated list of font family names to be used for @dfn{bitmap}
or @dfn{ass} type subtitle rendering.
Only first font name is used for @dfn{ass} type subtitle.

If not specified, use internaly defined default font family.

@item -ass_single_rect @var{boolean}
ARIB STD-B24 specifies that some captions may be displayed at different
positions at a time (multi-rectangle subtitle).
Since some players (e.g., old @dfn{mpv}) can't handle multiple ASS rectangles
in a single AVSubtitle, or multiple ASS rectangles of indeterminate duration
with the same start timestamp, this option can change the behavior so that
all the texts are displayed in a single ASS rectangle.

The default is @var{false}.

If your player cannot handle AVSubtitles with multiple ASS rectangles properly,
set this option to @var{true} or define @env{ASS_SINGLE_RECT=1} to change
default behavior at compilation.

@item -force_outline_text @var{boolean}
Specify whether always render outline text for all characters regardless of
the indication by charactor style.

The default is @var{false}.

@item -outline_width @var{number} (0.0 - 3.0)
Specify width for outline text, in dots (relative).

The default is @var{1.5}.

@item -ignore_background @var{boolean}
Specify whether to ignore background color rendering.

The default is @var{false}.

@item -ignore_ruby @var{boolean}
Specify whether to ignore rendering for ruby-like (furigana) characters.

The default is @var{false}.

@item -replace_drcs @var{boolean}
Specify whether to render replaced DRCS characters as Unicode characters.

The default is @var{true}.

@item -replace_msz_ascii @var{boolean}
Specify whether to replace MSZ (Middle Size; half width) fullwidth
alphanumerics with halfwidth alphanumerics.

The default is @var{true}.

@item -replace_msz_japanese @var{boolean}
Specify whether to replace some MSZ (Middle Size; half width) fullwidth
japanese special characters with halfwidth ones.

The default is @var{true}.

@item -replace_msz_glyph @var{boolean}
Specify whether to replace MSZ (Middle Size; half width) characters
with halfwidth glyphs if the fonts supports it.
This option works under FreeType or DirectWrite renderer
with Adobe-Japan1 compliant fonts.
e.g., IBM Plex Sans JP, Morisawa BIZ UDGothic, Morisawa BIZ UDMincho,
Yu Gothic, Yu Mincho, and Meiryo.

The default is @var{true}.

@item -canvas_size @var{image_size}
Specify the resolution of the canvas to render subtitles to; usually, this
should be frame size of input video.
This only applies when @code{-subtitle_type} is set to @var{bitmap}.

The libaribcaption decoder assumes input frame size for bitmap rendering as below:
@enumerate
@item
PROFILE_A : 1440 x 1080 with SAR (PAR) 4:3
@item
PROFILE_C : 320 x 180 with SAR (PAR) 1:1
@end enumerate

If actual frame size of input video does not match above assumption,
the rendered captions may be distorted.
To make the captions undistorted, add @code{-canvas_size} option to specify
actual input video size.

Note that the @code{-canvas_size} option is not required for video with
different size but same aspect ratio.
In such cases, the caption will be stretched or shrunk to actual video size
if @code{-canvas_size} option is not specified.
If @code{-canvas_size} option is specified with different size,
the caption will be stretched or shrunk as specified size with calculated SAR.

@end table

@subsection libaribcaption decoder usage examples

Display MPEG-TS file with ARIB subtitle by @code{ffplay} tool:
@example
ffplay -sub_type bitmap MPEG.TS
@end example

Display MPEG-TS file with input frame size 1920x1080 by @code{ffplay} tool:
@example
ffplay -sub_type bitmap -canvas_size 1920x1080 MPEG.TS
@end example

Embed ARIB subtitle in transcoded video:
@example
ffmpeg -sub_type bitmap -i src.m2t -filter_complex "[0:v][0:s]overlay" -vcodec h264 dest.mp4
@end example

@section dvbsub

@subsection Options

@table @option
@item compute_clut
@table @option
@item -2
Compute clut once if no matching CLUT is in the stream.
@item -1
Compute clut if no matching CLUT is in the stream.
@item 0
Never compute CLUT
@item 1
Always compute CLUT and override the one provided in the stream.
@end table
@item dvb_substream
Selects the dvb substream, or all substreams if -1 which is default.

@end table

@section dvdsub

This codec decodes the bitmap subtitles used in DVDs; the same subtitles can
also be found in VobSub file pairs and in some Matroska files.

@subsection Options

@table @option
@item palette
Specify the global palette used by the bitmaps. When stored in VobSub, the
palette is normally specified in the index file; in Matroska, the palette is
stored in the codec extra-data in the same format as in VobSub. In DVDs, the
palette is stored in the IFO file, and therefore not available when reading
from dumped VOB files.

The format for this option is a string containing 16 24-bits hexadecimal
numbers (without 0x prefix) separated by commas, for example @code{0d00ee,
ee450d, 101010, eaeaea, 0ce60b, ec14ed, ebff0b, 0d617a, 7b7b7b, d1d1d1,
7b2a0e, 0d950c, 0f007b, cf0dec, cfa80c, 7c127b}.

@item ifo_palette
Specify the IFO file from which the global palette is obtained.
(experimental)

@item forced_subs_only
Only decode subtitle entries marked as forced. Some titles have forced
and non-forced subtitles in the same track. Setting this flag to @code{1}
will only keep the forced subtitles. Default value is @code{0}.
@end table

@section libzvbi-teletext

Libzvbi allows libavcodec to decode DVB teletext pages and DVB teletext
subtitles. Requires the presence of the libzvbi headers and library during
configuration. You need to explicitly configure the build with
@code{--enable-libzvbi}.

@subsection Options

@table @option
@item txt_page
List of teletext page numbers to decode. Pages that do not match the specified
list are dropped. You may use the special @code{*} string to match all pages,
or @code{subtitle} to match all subtitle pages.
Default value is *.
@item txt_default_region
Set default character set used for decoding, a value between 0 and 87 (see
ETS 300 706, Section 15, Table 32). Default value is -1, which does not
override the libzvbi default. This option is needed for some legacy level 1.0
transmissions which cannot signal the proper charset.
@item txt_chop_top
Discards the top teletext line. Default value is 1.
@item txt_format
Specifies the format of the decoded subtitles.
@table @option
@item bitmap
The default format, you should use this for teletext pages, because certain
graphics and colors cannot be expressed in simple text or even ASS.
@item text
Simple text based output without formatting.
@item ass
Formatted ASS output, subtitle pages and teletext pages are returned in
different styles, subtitle pages are stripped down to text, but an effort is
made to keep the text alignment and the formatting.
@end table
@item txt_left
X offset of generated bitmaps, default is 0.
@item txt_top
Y offset of generated bitmaps, default is 0.
@item txt_chop_spaces
Chops leading and trailing spaces and removes empty lines from the generated
text. This option is useful for teletext based subtitles where empty spaces may
be present at the start or at the end of the lines or empty lines may be
present between the subtitle lines because of double-sized teletext characters.
Default value is 1.
@item txt_duration
Sets the display duration of the decoded teletext pages or subtitles in
milliseconds. Default value is -1 which means infinity or until the next
subtitle event comes.
@item txt_transparent
Force transparent background of the generated teletext bitmaps. Default value
is 0 which means an opaque background.
@item txt_opacity
Sets the opacity (0-255) of the teletext background. If
@option{txt_transparent} is not set, it only affects characters between a start
box and an end box, typically subtitles. Default value is 0 if
@option{txt_transparent} is set, 255 otherwise.

@end table

@c man end SUBTILES DECODERS