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295 lines
8.7 KiB
Plaintext
295 lines
8.7 KiB
Plaintext
@chapter Decoders
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@c man begin DECODERS
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Decoders are configured elements in FFmpeg which allow the decoding of
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multimedia streams.
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When you configure your FFmpeg build, all the supported native decoders
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are enabled by default. Decoders requiring an external library must be enabled
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manually via the corresponding @code{--enable-lib} option. You can list all
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available decoders using the configure option @code{--list-decoders}.
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You can disable all the decoders with the configure option
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@code{--disable-decoders} and selectively enable / disable single decoders
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with the options @code{--enable-decoder=@var{DECODER}} /
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@code{--disable-decoder=@var{DECODER}}.
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The option @code{-decoders} of the ff* tools will display the list of
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enabled decoders.
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@c man end DECODERS
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@chapter Video Decoders
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@c man begin VIDEO DECODERS
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A description of some of the currently available video decoders
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follows.
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@section hevc
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HEVC / H.265 decoder.
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Note: the @option{skip_loop_filter} option has effect only at level
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@code{all}.
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@section rawvideo
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Raw video decoder.
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This decoder decodes rawvideo streams.
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@subsection Options
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@table @option
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@item top @var{top_field_first}
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Specify the assumed field type of the input video.
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@table @option
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@item -1
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the video is assumed to be progressive (default)
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@item 0
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bottom-field-first is assumed
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@item 1
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top-field-first is assumed
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@end table
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@end table
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@c man end VIDEO DECODERS
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@chapter Audio Decoders
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@c man begin AUDIO DECODERS
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A description of some of the currently available audio decoders
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follows.
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@section ac3
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AC-3 audio decoder.
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This decoder implements part of ATSC A/52:2010 and ETSI TS 102 366, as well as
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the undocumented RealAudio 3 (a.k.a. dnet).
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@subsection AC-3 Decoder Options
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@table @option
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@item -drc_scale @var{value}
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Dynamic Range Scale Factor. The factor to apply to dynamic range values
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from the AC-3 stream. This factor is applied exponentially.
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There are 3 notable scale factor ranges:
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@table @option
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@item drc_scale == 0
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DRC disabled. Produces full range audio.
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@item 0 < drc_scale <= 1
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DRC enabled. Applies a fraction of the stream DRC value.
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Audio reproduction is between full range and full compression.
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@item drc_scale > 1
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DRC enabled. Applies drc_scale asymmetrically.
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Loud sounds are fully compressed. Soft sounds are enhanced.
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@end table
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@end table
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@section flac
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FLAC audio decoder.
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This decoder aims to implement the complete FLAC specification from Xiph.
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@subsection FLAC Decoder options
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@table @option
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@item -use_buggy_lpc
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The lavc FLAC encoder used to produce buggy streams with high lpc values
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(like the default value). This option makes it possible to decode such streams
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correctly by using lavc's old buggy lpc logic for decoding.
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@end table
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@section ffwavesynth
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Internal wave synthetizer.
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This decoder generates wave patterns according to predefined sequences. Its
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use is purely internal and the format of the data it accepts is not publicly
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documented.
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@section libcelt
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libcelt decoder wrapper.
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libcelt allows libavcodec to decode the Xiph CELT ultra-low delay audio codec.
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Requires the presence of the libcelt headers and library during configuration.
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You need to explicitly configure the build with @code{--enable-libcelt}.
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@section libgsm
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libgsm decoder wrapper.
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libgsm allows libavcodec to decode the GSM full rate audio codec. Requires
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the presence of the libgsm headers and library during configuration. You need
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to explicitly configure the build with @code{--enable-libgsm}.
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This decoder supports both the ordinary GSM and the Microsoft variant.
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@section libilbc
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libilbc decoder wrapper.
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libilbc allows libavcodec to decode the Internet Low Bitrate Codec (iLBC)
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audio codec. Requires the presence of the libilbc headers and library during
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configuration. You need to explicitly configure the build with
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@code{--enable-libilbc}.
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@subsection Options
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The following option is supported by the libilbc wrapper.
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@table @option
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@item enhance
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Enable the enhancement of the decoded audio when set to 1. The default
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value is 0 (disabled).
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@end table
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@section libopencore-amrnb
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libopencore-amrnb decoder wrapper.
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libopencore-amrnb allows libavcodec to decode the Adaptive Multi-Rate
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Narrowband audio codec. Using it requires the presence of the
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libopencore-amrnb headers and library during configuration. You need to
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explicitly configure the build with @code{--enable-libopencore-amrnb}.
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An FFmpeg native decoder for AMR-NB exists, so users can decode AMR-NB
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without this library.
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@section libopencore-amrwb
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libopencore-amrwb decoder wrapper.
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libopencore-amrwb allows libavcodec to decode the Adaptive Multi-Rate
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Wideband audio codec. Using it requires the presence of the
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libopencore-amrwb headers and library during configuration. You need to
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explicitly configure the build with @code{--enable-libopencore-amrwb}.
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An FFmpeg native decoder for AMR-WB exists, so users can decode AMR-WB
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without this library.
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@section libopus
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libopus decoder wrapper.
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libopus allows libavcodec to decode the Opus Interactive Audio Codec.
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Requires the presence of the libopus headers and library during
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configuration. You need to explicitly configure the build with
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@code{--enable-libopus}.
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An FFmpeg native decoder for Opus exists, so users can decode Opus
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without this library.
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@c man end AUDIO DECODERS
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@chapter Subtitles Decoders
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@c man begin SUBTILES DECODERS
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@section dvbsub
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@subsection Options
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@table @option
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@item compute_clut
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@table @option
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@item -1
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Compute clut if no matching CLUT is in the stream.
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@item 0
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Never compute CLUT
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@item 1
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Always compute CLUT and override the one provided in the stream.
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@end table
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@item dvb_substream
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Selects the dvb substream, or all substreams if -1 which is default.
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@end table
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@section dvdsub
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This codec decodes the bitmap subtitles used in DVDs; the same subtitles can
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also be found in VobSub file pairs and in some Matroska files.
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@subsection Options
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@table @option
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@item palette
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Specify the global palette used by the bitmaps. When stored in VobSub, the
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palette is normally specified in the index file; in Matroska, the palette is
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stored in the codec extra-data in the same format as in VobSub. In DVDs, the
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palette is stored in the IFO file, and therefore not available when reading
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from dumped VOB files.
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The format for this option is a string containing 16 24-bits hexadecimal
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numbers (without 0x prefix) separated by comas, for example @code{0d00ee,
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ee450d, 101010, eaeaea, 0ce60b, ec14ed, ebff0b, 0d617a, 7b7b7b, d1d1d1,
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7b2a0e, 0d950c, 0f007b, cf0dec, cfa80c, 7c127b}.
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@item ifo_palette
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Specify the IFO file from which the global palette is obtained.
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(experimental)
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@item forced_subs_only
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Only decode subtitle entries marked as forced. Some titles have forced
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and non-forced subtitles in the same track. Setting this flag to @code{1}
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will only keep the forced subtitles. Default value is @code{0}.
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@end table
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@section libzvbi-teletext
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Libzvbi allows libavcodec to decode DVB teletext pages and DVB teletext
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subtitles. Requires the presence of the libzvbi headers and library during
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configuration. You need to explicitly configure the build with
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@code{--enable-libzvbi}.
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@subsection Options
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@table @option
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@item txt_page
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List of teletext page numbers to decode. You may use the special * string to
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match all pages. Pages that do not match the specified list are dropped.
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Default value is *.
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@item txt_chop_top
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Discards the top teletext line. Default value is 1.
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@item txt_format
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Specifies the format of the decoded subtitles. The teletext decoder is capable
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of decoding the teletext pages to bitmaps or to simple text, you should use
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"bitmap" for teletext pages, because certain graphics and colors cannot be
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expressed in simple text. You might use "text" for teletext based subtitles if
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your application can handle simple text based subtitles. Default value is
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bitmap.
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@item txt_left
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X offset of generated bitmaps, default is 0.
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@item txt_top
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Y offset of generated bitmaps, default is 0.
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@item txt_chop_spaces
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Chops leading and trailing spaces and removes empty lines from the generated
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text. This option is useful for teletext based subtitles where empty spaces may
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be present at the start or at the end of the lines or empty lines may be
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present between the subtitle lines because of double-sized teletext charactes.
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Default value is 1.
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@item txt_duration
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Sets the display duration of the decoded teletext pages or subtitles in
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milliseconds. Default value is 30000 which is 30 seconds.
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@item txt_transparent
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Force transparent background of the generated teletext bitmaps. Default value
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is 0 which means an opaque background.
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@item txt_opacity
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Sets the opacity (0-255) of the teletext background. If
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@option{txt_transparent} is not set, it only affects characters between a start
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box and an end box, typically subtitles. Default value is 0 if
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@option{txt_transparent} is set, 255 otherwise.
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@end table
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@c man end SUBTILES DECODERS
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