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287 lines
8.6 KiB
287 lines
8.6 KiB
@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 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 synthesizer. |
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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 characters. |
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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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