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206 lines
8.6 KiB
XML
206 lines
8.6 KiB
XML
<glossary>
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<warning> <para>
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Please note that this book is in no way a reference documentation
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on how DVDs work. Its only purpose is to describe the API
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available for programmers in VLC media player. It is assumed that
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you have basic knowledge of what MPEG is. The following paragraph
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is just here as a reminder :
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</para> </warning>
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<glossentry>
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<glossterm> <acronym> AC3 </acronym> :
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Digital Audio Compression Standard </glossterm>
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<glossdef> <para> Specification for coding audio data, used in DVD.
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The documentation is
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<ulink url="http://www.linuxvideo.org/devel/library/ac3-standard_a_52.pdf">
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freely available </ulink>.
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</para> </glossdef>
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</glossentry>
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<glossentry>
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<glossterm> <acronym> B </acronym> (bi-directional) picture </glossterm>
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<glossdef> <para> Picture decoded from its own data, <emphasis>
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and </emphasis> from the data of the previous and next (that
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means <emphasis>in the future</emphasis>) reference
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pictures (I or P pictures). It is the most compressed picture
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format, but it is less fault-tolerant.
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</para> </glossdef>
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</glossentry>
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<glossentry>
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<glossterm> <acronym> DVD </acronym> :
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Digital Versatile Disc </glossterm>
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<glossdef> <para> Disc hardware format, using the UDF file system,
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an extension of the ISO 9660 file system format and a video format
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which is an extension of the MPEG-2 specification.
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It basically uses MPEG-2 PS files, with subtitles and sound
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tracks encoded as private data and fed into non-MPEG decoders,
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along with .ifo files describing the contents of the DVD. DVD
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specifications are very hard to get, and it takes some
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time to reverse-engineer it. Sometimes DVD are zoned and
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scrambled, so we use a brute-force algorithm to find the key.
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</para> </glossdef>
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</glossentry>
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<glossentry>
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<glossterm> <acronym> ES </acronym> : Elementary Stream </glossterm>
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<glossdef> <para> Continuous stream of data fed into a decoder,
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without any multiplexing layer. ES streams can be MPEG video
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MPEG audio, AC3 audio, LPCM audio, SPU subpictures...
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</para> </glossdef>
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</glossentry>
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<glossentry>
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<glossterm> Field picture </glossterm>
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<glossdef> <para> Picture split in two fields, even and odd, like
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television does. DVDs coming from TV shows typically use field
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pictures.
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</para> </glossdef>
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</glossentry>
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<glossentry>
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<glossterm> Frame picture </glossterm>
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<glossdef> <para> Picture without even/odd discontinuities, unlike
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field pictures. DVDs coming from movies typically use frame
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pictures.
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</para> </glossdef>
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</glossentry>
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<glossentry>
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<glossterm> <acronym>I</acronym> (intra) picture </glossterm>
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<glossdef> <para> Picture independantly coded. It can be
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decoded without any other reference frame. It is regularly
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sent (like twice a second) for resynchronization purposes.
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</para> </glossdef>
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</glossentry>
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<glossentry>
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<glossterm> <acronym> IDCT </acronym> : Inverse Discrete
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Cosinus Transform </glossterm>
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<glossdef> <para> IDCT is a classical mathematical algorithm
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to convert from a space domain to a frequency domain. In a
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nutshell, it codes differences instead of coding all absolute
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pixels. MPEG uses an 2-D IDCT in the video decoder, and a 1-D
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IDCT in the audio decoder.
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</para> </glossdef>
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</glossentry>
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<glossentry>
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<glossterm> <acronym> LPCM </acronym> :
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Linear Pulse Code Modulation </glossterm>
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<glossdef> <para> LPCM is a non-compressed audio encoding,
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available in DVDs.
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</para> </glossdef>
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</glossentry>
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<glossentry>
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<glossterm> <acronym> MPEG </acronym> :
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Motion Picture Expert Group </glossterm>
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<glossdef> <para> Specification describing a standard syntax of files
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and streams for carrying motion pictures and sound. MPEG-1 is
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ISO/IEC 11172 (three books), MPEG-2 is ISO/IEC 13818. MPEG-4
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version 1 is out, but this player doesn't support it. It is
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relatively easy to get an MPEG specification from ISO or
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equivalent, drafts are even freely available on the Internet.
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</para> </glossdef>
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</glossentry>
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<glossentry>
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<glossterm> <acronym> P </acronym> (predictive) picture </glossterm>
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<glossdef> <para> Picture decoded from its own data <emphasis>
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and </emphasis> data from a reference picture, which is the
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last I or P picture received.
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</para> </glossdef>
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</glossentry>
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<glossentry>
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<glossterm> <acronym> PES </acronym> :
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Packetized Elementary Stream </glossterm>
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<glossdef> <para> A chunk of elementary stream. It often corresponds
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to a logical boundary of the stream (for instance a picture
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change), but it is not mandatory. PES carry the synchronization
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information.
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</para> </glossdef>
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</glossentry>
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<glossentry>
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<glossterm> <acronym> PTS </acronym> :
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Presentation Time Stamp </glossterm>
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<glossdef> <para> Time at which the content of a PES packet is supposed
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to be played. It is used for A/V synchronization.
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</para> </glossdef>
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</glossentry>
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<glossentry>
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<glossterm> <acronym> PS </acronym> : Program Stream </glossterm>
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<glossdef> <para> File format obtained by concatenating PES packets
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and inserting Pack headers and System headers (for timing
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information). It is the only format described in MPEG-1, and
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the most used format in MPEG-2.
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</para></glossdef>
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</glossentry>
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<glossentry>
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<glossterm> <acronym> RGB </acronym> : Red Green Blue </glossterm>
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<glossdef> <para> Picture format where every pixel is calculated in a
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vector space whose coordinates are red, green, and blue. This
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is natively used by monitors and TV sets.
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</para> </glossdef>
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</glossentry>
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<glossentry>
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<glossterm> <acronym> SPU </acronym> : Sub Picture Unit </glossterm>
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<glossdef> <para> Picture format allowing to do overlays, such
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as subtitles or DVD menus.
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</para> </glossdef>
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</glossentry>
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<glossentry>
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<glossterm> <acronym> SCR </acronym> :
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System Clock Reference </glossterm>
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<glossdef> <para> Time at which the first byte of a particular pack
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is supposed to be fed to the decoder. VLC uses it to read the
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stream at the right pace.
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</para> </glossdef>
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</glossentry>
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<glossentry>
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<glossterm> <acronym> SDL </acronym> :
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Simple DirectMedia Layer </glossterm>
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<glossdef> <para> <ulink url="http://www.libsdl.org/"> SDL </ulink>
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is a cross-platform multimedia library
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designed to provide fast access to the video framebuffer and
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the audio device. Since version 1.1, it features YUV overlay
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support, which reduces decoding times by a third.
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</para> </glossdef>
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</glossentry>
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<glossentry>
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<glossterm> <acronym> TS </acronym> : Transport Stream </glossterm>
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<glossdef> <para> Stream format constituted of fixed size packets
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(188 bytes), defined by ISO/IEC 13818-1. PES packets are
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split among several TS packets.
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A TS stream can contain several programs. It is used in
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streaming applications, in particular for satellite or cable
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broadcasting.
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</para> </glossdef>
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</glossentry>
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<glossentry>
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<glossterm> <acronym> YUV </acronym> :
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Luminance/Chrominance </glossterm>
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<glossdef> <para> Picture format with 1 coordinate of luminance (black
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and white) and 2 coordinates of chrominance (red and blue).
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This is natively used by PAL video system, for backward
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compatibility with older black and white TV sets. Your eyes
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distinguish luminance variations much better than chrominance
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variations, so you can compress them more. It is therefore
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well suited for image compression, and is used by the MPEG
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specification. The RGB picture can be obtained from the YUV one
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via a costly matrix multiply operation, which can be done in
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hardware by most modern video cards ("YUV acceleration").
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</para> </glossdef>
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</glossentry>
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</glossary>
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