1@chapter Decoders 2@c man begin DECODERS 3 4Decoders are configured elements in FFmpeg which allow the decoding of 5multimedia streams. 6 7When you configure your FFmpeg build, all the supported native decoders 8are enabled by default. Decoders requiring an external library must be enabled 9manually via the corresponding @code{--enable-lib} option. You can list all 10available decoders using the configure option @code{--list-decoders}. 11 12You can disable all the decoders with the configure option 13@code{--disable-decoders} and selectively enable / disable single decoders 14with the options @code{--enable-decoder=@var{DECODER}} / 15@code{--disable-decoder=@var{DECODER}}. 16 17The option @code{-decoders} of the ff* tools will display the list of 18enabled decoders. 19 20@c man end DECODERS 21 22@chapter Video Decoders 23@c man begin VIDEO DECODERS 24 25A description of some of the currently available video decoders 26follows. 27 28@section rawvideo 29 30Raw video decoder. 31 32This decoder decodes rawvideo streams. 33 34@subsection Options 35 36@table @option 37@item top @var{top_field_first} 38Specify the assumed field type of the input video. 39@table @option 40@item -1 41the video is assumed to be progressive (default) 42@item 0 43bottom-field-first is assumed 44@item 1 45top-field-first is assumed 46@end table 47 48@end table 49 50@c man end VIDEO DECODERS 51 52@chapter Audio Decoders 53@c man begin AUDIO DECODERS 54 55A description of some of the currently available audio decoders 56follows. 57 58@section ac3 59 60AC-3 audio decoder. 61 62This decoder implements part of ATSC A/52:2010 and ETSI TS 102 366, as well as 63the undocumented RealAudio 3 (a.k.a. dnet). 64 65@subsection AC-3 Decoder Options 66 67@table @option 68 69@item -drc_scale @var{value} 70Dynamic Range Scale Factor. The factor to apply to dynamic range values 71from the AC-3 stream. This factor is applied exponentially. 72There are 3 notable scale factor ranges: 73@table @option 74@item drc_scale == 0 75DRC disabled. Produces full range audio. 76@item 0 < drc_scale <= 1 77DRC enabled. Applies a fraction of the stream DRC value. 78Audio reproduction is between full range and full compression. 79@item drc_scale > 1 80DRC enabled. Applies drc_scale asymmetrically. 81Loud sounds are fully compressed. Soft sounds are enhanced. 82@end table 83 84@end table 85 86@section ffwavesynth 87 88Internal wave synthetizer. 89 90This decoder generates wave patterns according to predefined sequences. Its 91use is purely internal and the format of the data it accepts is not publicly 92documented. 93 94@section libcelt 95 96libcelt decoder wrapper. 97 98libcelt allows libavcodec to decode the Xiph CELT ultra-low delay audio codec. 99Requires the presence of the libcelt headers and library during configuration. 100You need to explicitly configure the build with @code{--enable-libcelt}. 101 102@section libgsm 103 104libgsm decoder wrapper. 105 106libgsm allows libavcodec to decode the GSM full rate audio codec. Requires 107the presence of the libgsm headers and library during configuration. You need 108to explicitly configure the build with @code{--enable-libgsm}. 109 110This decoder supports both the ordinary GSM and the Microsoft variant. 111 112@section libilbc 113 114libilbc decoder wrapper. 115 116libilbc allows libavcodec to decode the Internet Low Bitrate Codec (iLBC) 117audio codec. Requires the presence of the libilbc headers and library during 118configuration. You need to explicitly configure the build with 119@code{--enable-libilbc}. 120 121@subsection Options 122 123The following option is supported by the libilbc wrapper. 124 125@table @option 126@item enhance 127 128Enable the enhancement of the decoded audio when set to 1. The default 129value is 0 (disabled). 130 131@end table 132 133@section libopencore-amrnb 134 135libopencore-amrnb decoder wrapper. 136 137libopencore-amrnb allows libavcodec to decode the Adaptive Multi-Rate 138Narrowband audio codec. Using it requires the presence of the 139libopencore-amrnb headers and library during configuration. You need to 140explicitly configure the build with @code{--enable-libopencore-amrnb}. 141 142An FFmpeg native decoder for AMR-NB exists, so users can decode AMR-NB 143without this library. 144 145@section libopencore-amrwb 146 147libopencore-amrwb decoder wrapper. 148 149libopencore-amrwb allows libavcodec to decode the Adaptive Multi-Rate 150Wideband audio codec. Using it requires the presence of the 151libopencore-amrwb headers and library during configuration. You need to 152explicitly configure the build with @code{--enable-libopencore-amrwb}. 153 154An FFmpeg native decoder for AMR-WB exists, so users can decode AMR-WB 155without this library. 156 157@section libopus 158 159libopus decoder wrapper. 160 161libopus allows libavcodec to decode the Opus Interactive Audio Codec. 162Requires the presence of the libopus headers and library during 163configuration. You need to explicitly configure the build with 164@code{--enable-libopus}. 165 166@c man end AUDIO DECODERS 167 168@chapter Subtitles Decoders 169@c man begin SUBTILES DECODERS 170 171@section dvdsub 172 173This codec decodes the bitmap subtitles used in DVDs; the same subtitles can 174also be found in VobSub file pairs and in some Matroska files. 175 176@subsection Options 177 178@table @option 179@item palette 180Specify the global palette used by the bitmaps. When stored in VobSub, the 181palette is normally specified in the index file; in Matroska, the palette is 182stored in the codec extra-data in the same format as in VobSub. In DVDs, the 183palette is stored in the IFO file, and therefore not available when reading 184from dumped VOB files. 185 186The format for this option is a string containing 16 24-bits hexadecimal 187numbers (without 0x prefix) separated by comas, for example @code{0d00ee, 188ee450d, 101010, eaeaea, 0ce60b, ec14ed, ebff0b, 0d617a, 7b7b7b, d1d1d1, 1897b2a0e, 0d950c, 0f007b, cf0dec, cfa80c, 7c127b}. 190@end table 191 192@section libzvbi-teletext 193 194Libzvbi allows libavcodec to decode DVB teletext pages and DVB teletext 195subtitles. Requires the presence of the libzvbi headers and library during 196configuration. You need to explicitly configure the build with 197@code{--enable-libzvbi}. 198 199@subsection Options 200 201@table @option 202@item txt_page 203List of teletext page numbers to decode. You may use the special * string to 204match all pages. Pages that do not match the specified list are dropped. 205Default value is *. 206@item txt_chop_top 207Discards the top teletext line. Default value is 1. 208@item txt_format 209Specifies the format of the decoded subtitles. The teletext decoder is capable 210of decoding the teletext pages to bitmaps or to simple text, you should use 211"bitmap" for teletext pages, because certain graphics and colors cannot be 212expressed in simple text. You might use "text" for teletext based subtitles if 213your application can handle simple text based subtitles. Default value is 214bitmap. 215@item txt_left 216X offset of generated bitmaps, default is 0. 217@item txt_top 218Y offset of generated bitmaps, default is 0. 219@item txt_chop_spaces 220Chops leading and trailing spaces and removes empty lines from the generated 221text. This option is useful for teletext based subtitles where empty spaces may 222be present at the start or at the end of the lines or empty lines may be 223present between the subtitle lines because of double-sized teletext charactes. 224Default value is 1. 225@item txt_duration 226Sets the display duration of the decoded teletext pages or subtitles in 227miliseconds. Default value is 30000 which is 30 seconds. 228@item txt_transparent 229Force transparent background of the generated teletext bitmaps. Default value 230is 0 which means an opaque (black) background. 231@end table 232 233@c man end SUBTILES DECODERS 234