123 lines
7.6 KiB
HTML
123 lines
7.6 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//RU">
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<!-- Copyright (c) 2001 Josh Coalson -->
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<HTML>
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<META CHARSET="windows-1251">
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<TITLE>FLAC: õàðàêòåðèñòèêè</TITLE>
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<CENTER><TABLE cellpadding=0 cellspacing=0 border=0>
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<TR>
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<TD height=22 align=center nowrap>
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<A HREF="index.html">íà÷àëî</A> </TD>
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<TD align=center nowrap>
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<A HREF="news.html">íîâîñòè</A> </TD>
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<TD align=center nowrap>
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<A HREF="download.html">ôàéëû</A> </TD>
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õàðàêòåðèñòèêè </TD>
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<A HREF="goals.html">öåëè</A> </TD>
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<A HREF="format.html">ôîðìàò</A> </TD>
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<TD align=center>|</TD></TR>
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<TR>
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<TD align=center>|</TD>
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<TD align=center nowrap>
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<A HREF="id.html">id</A> </TD>
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<TD align=center nowrap>
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<A HREF="comparison.html">ñðàâíåíèå</A> </TD>
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<TD align=center nowrap>
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<A HREF="developers.html">ðàçðàáîòêà</A> </TD>
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<TD align=center nowrap>
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<A HREF="documentation.html">äîêóìåíòàöèÿ</A> </TD>
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<TD align=center nowrap>
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<A HREF="links.html">ññûëêè</A> </TD>
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<TD align=center nowrap>
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<A HREF="authors.html">àâòîðû</A> </TD>
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<TD align=center>|</TD></TR>
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</TR></TABLE></CENTER>
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<CENTER><H2>FLAC: õàðàêòåðèñòèêè</H2></CENTER>
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<P>FLAC - ýòî àááðåâèàòóðà îò free lossless audio codec (ñâîáîäíûé êîäåê, îáåñïå÷èâàþùèé ñæàòèå áåç ïîòåðü). Ïðîåêò FLAC âêëþ÷àåò:</P>
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<P><BLOCKQUOTE><UL>
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<LI>ïîòîêîâûé ôîðìàò</LI>
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<LI>áèáëèîòåêó <B>libFLAC</B>, ðåàëèçóþùóþ áàçîâûé åíêîäåðû è äåêîäåðû.</LI>
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<LI><B>flac</B>, óòèëèòó êîìàíäíîé ñòðîêè, âûïîëíÿþùóþ ñæàòèå è ðàñïàêîâêó .flac ôàéëîâ.</LI>
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<LI>Ïëàãèíû äëÿ ðàçíûõ ïëåéåðîâ (Winamp, XMMS, âåäåòñÿ ðàáîòà íàä äðóãèìè).</LI>
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</UL></BLOCKQUOTE></P>
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<P>"Ñâîáîäà" îçíà÷àåò, ÷òî ñïåöèôèêàöèÿ ïîòîêîâîãî ôîðìàòà îòíîñèòñÿ ê êàòåãîðèè public domain (ïðîåêò FLAC îñòàâëÿåò çà ñîáîé ïðàâî óñòàíàâëèâàòü ñïåöèôèêàöèè è ñåðòèôèöèðîâàòü îòíîñÿùèåñÿ ê íåìó ïðîäóêòû íà ñîâìåñòèìîñòü), à òàêæå òî, ÷òî íè ôîðìàò, íè îäèí èç ðåàëèçîâàííûõ ìåòîäîâ êîäèðîâàíèÿ/äåêîäèðîâàíèÿ íå çàïàòåíòîâàíû. Ýòî òàêæå çíà÷èò, ÷òî èñõîäíèêè <B><TT>libFLAC</TT></B> äîñòóïíû ïî ëèöåíçèè LGPL, à èñõîäíèêè <B><TT>flac</TT></B> è ïëàãèíîâ - ïî GPL.</P>
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<P>Õàðàêòåðèñòèêè FLAC:</P>
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<P><BLOCKQUOTE><UL>
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<LI>Ôîðìàò FLAC è ìåòîäû êîäèðîâàíèÿ/äåêîäèðîâàíèÿ íå çàùèùåíû ïàòåíòàìè.</LI>
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<LI>FLAC ñæèìàåò ôàéëû áåç ïîòåðü. Êîäèðîâàíèå PCM äàííûõ íå ïðèâîäèò ê ïîòåðå èíôîðìàöèè, ñëåäîâàòåëüíî, äåêîäèðóåìûé àóäèîôàéë àáñîëþòíî èäåíòè÷åí òîìó, êîòîðûé áûë ïîäàí íà âõîä åíêîäåðó. ×òîáû îïðåäåëèòü âîçìîæíûå îøèáêè ïðè ïåðåäà÷å ôàéëà, äëÿ êàæäîãî ôðåéìà âû÷èñëÿåòñÿ 16-áèòíàÿ êîíòðîëüíàÿ ñóììà. Öåëîñòíîñòü íà äàëüíåéøåì ýòàïå ïîäòâåðæäàåòñÿ ïîäïèñüþ <A HREF="http://userpages.umbc.edu/~mabzug1/cs/md5/md5.html">MD5</A> ðàñïàêîâàííûõ äàííûõ, êîòîðàÿ íàõîäèòñÿ â çàãîëîâêå è ìîæåò áûòü ïðîâåðåíà ïðè âîñïðîèçâåäåíèè, äåêîäèðîâàíèè èëè ñ ïîìîùüþ òåñòèðîâàíèÿ.</LI>
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<LI>FLAC ðàçðàáîòàí äëÿ ñæàòèÿ àóäèîäàííûõ. Òåîðåòè÷åñêè, <B><TT>flac</TT></B> ìîæåò êîìïðåññèðîâàòü áåç ïîòåðü ëþáûå äðóãèå äàííûå (åñëè ïåðåäàâàòü èõ êàê 8-áèòíûé ìîíî raw-ôàéë), îäíàêî âûõîäíûå ôàéëû ïîëó÷àþòñÿ ïî÷òè òàêîãî æå ðàçìåðà.</LI>
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<LI>Âîçìîæíîñòè ñæàòèÿ âî FLAC ðàñøèðÿåìû. Ýòî îçíà÷àåò, ÷òî â áóäóùèõ âåðñèÿõ ôîðìàòà ìîãóò áûòü äîáàâëåíû íîâûå ìåòîäû áåç ïîòåðè îáðàòíîé ñîâìåñòèìîñòè.</LI>
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<LI>Ðåàëèçîâàííûå íà äàííûé ìîìåíò ìåòîäû êîìïðåññèè ñîçäàþò ïîòîêè ìåíüøåãî ðàçìåðà, ÷åì <A HREF="http://www.softsound.com/Shorten.html">Shorten</A> (êîäåê ñ îòêðûòûìè èñõîäíèêàìè, ÿâëÿþùèéñÿ òåêóùèì ñòàíäàðòîì ñæàòèÿ áåç ïîòåðü "ó íèõ"). Âðåìÿ êîäèðîâàíèÿ çàâèñèò îò ìåòîäà, íî îáû÷íî ñðàâíèìî ñ <A HREF="http://www.softsound.com/Shorten.html">Shorten</A> è <A HREF="http://www.mp3dev.org/mp3/">LAME</A>. Ñàìûå àêòèâíûå ìåòîäû ìîãóò ðàáîòàòü î÷åíü ìåäëåííî. Ïîäðîáíåå îá ýòîì ìîæíî ïîñìîòðåòü íà ñòðàíèöå <A HREF="comparison.html">ñðàâíåíèå.</A></LI>
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<LI>FLAC ðàññ÷èòàí íà áûñòðîå äåêîäèðîâàíèå. Äåêîäèðîâàíèå â ðåàëüíîì âðåìåíè ëåãêî äîñòèæèìî äàæå íà ñòàðûõ êîìïüþòåðàõ, òàê êàê äëÿ íåãî òðåáóåòñÿ òîëüêî öåëî÷èñëåííàÿ àðèôìåòèêà.</LI>
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<LI>FLAC óäîáíî èñïîëüçîâàòü äëÿ àðõèâàöèè, òàê êàê ñæàòèå ñ åãî ïîìîùüþ íå ïðèâîäèò ê ïîòåðå èíôîðìàöèè. Âû íå ïðèâÿçàíû ê ôîðìàòó. Åñëè â áóäóùåì Âû ðåøèòå èñïîëüçîâàòü äðóãîé ôîðìàò, äàííûå áóäóò âîññòàíîâëåíû èç .flac ôàéëà â ïåðâîíà÷àëüíîì âèäå. Êðîìå êîíòðîëüíîé ñóììû ôðåéìà è ïîäïèñè <A HREF="http://userpages.umbc.edu/~mabzug1/cs/md5/md5.html">MD5</A>, óòèëèòà <B><TT>flac</TT></B> èìååò âîçìîæíîñòü ïðîâåðêè, èñïîëüçîâàíèå êîòîðîé ïðèâîäèò ê òîìó, ÷òî êîäèðóåìûé ïîòîê ñðàçó æå äåêîäèðóåòñÿ è ñðàâíèâàåòñÿ ñ èñõîäíûì. Åñëè ïðîèñõîäèò îøèáêà, åíêîäåð ïðåêðàùàåò ðàáîòó.</LI>
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<LI>FLAC - ïîòîêîâûé ôîðìàò. Ýòî çíà÷èò, ÷òî êàæäûé ôðåéì ñîäåðæèò äîñòàòî÷íî èíôîðìàöèè äëÿ ñîáñòâåííîãî äåêîäèðîâàíèÿ. Òåêóùèé ôðåéì FLAC íå çàâèñèò îò ïðåäûäóùèõ è ïîñëåäóþùèõ. FLAC èñïîëüçóåò êîäû ñèíõðîíèçàöèè è êîíòðîëüíûå ñóììû, ÷òî ïîçâîëÿåò äåêîäåðó áûñòðî âûáèðàòü ïîçèöèþ â òåêóùåì ïîòîêå.</LI>
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<LI>FLAC ïîääåðæèâàåò áûñòðûé è òî÷íûé ïîèñê, ÷òî ïîëåçíî íå òîëüêî ïðè âîñïðîèçâåäåíèè, íî è äàåò âîçìîæíîñòü èñïîëüçîâàòü FLAC â çâóêîâûõ ðåäàêòîðàõ.</LI>
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<LI>FLAC èìååò ðàñøèðÿåìóþ ñèñòåìó ìåòàäàííûõ. Íîâûå áëîêè ìåòàäàííûõ ìîãóò áûòü îïðåäåëåíû è ðåàëèçîâàíû â áóäóùèõ âåðñèÿõ áåç ïîòåðè îáðàòíîé ñîâìåñòèìîñòè. Ïðèëîæåíèå ìîæåò èñïîëüçîâàòü áëîê ìåòàäàííûõ <A HREF="format.html#def_APPLICATION"><TT>APPLICATION</TT></A> ïîñëå ðåãèñòðàöèè äëÿ íåãî id. Äîáàâëåííûå òýãè ID3 è ID3v2 ê .flac ôàéëàì íå âëèÿþò íà ïîöåññ äåêîäèðîâàíèÿ.</LI>
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</UL></BLOCKQUOTE></P>
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<P>Íåêîòîðûå äîïîëíèòåëüíûå ïðåèìóùåñòâà, âûòåêàþùèå èç ïðèâåäåííûõ âûøå õàðàêòåðèñòèê:</P>
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<BLOCKQUOTE><P><UL>
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<LI>Ïîòîêè FLAC ìîãóò áûòü âîñïðîèçâåäåíû ñëèòíî, áåç ïàóç ìåæäó òðåêàìè. Òàêèì îáðàçîì, Âû ìîæåòå ñæàòü êîíöåðòíûé àëüáîì, ðàçäåëåííûé íà òðåêè, è äîáèòüñÿ åãî íåïðåðûâíîãî âîñïðîèçâåäåíèÿ.</LI>
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<LI>Ìåõàíèçì òî÷íîãî ïîèñêà ïîçâîëÿåò îðãàíèçîâûâàòü ðàçëè÷íûå ðåæèìû âîñïðîèçâåäåíèÿ: â ïëåéåðå ìîæíî ñäåëàòü èíäåêñíûé ïîèñê, ðàçëè÷íûå öèêëû èëè äðóãèå âèäû ñòðóêòóðèðîâàííîãî âîñïðîèçâåäåíèÿ. Ýòî î÷åíü ïîëåçíî, íàïðèìåð, äëÿ dj'åâ èëè äëÿ ðåïåòèöèé, êîãäà íóæíî ïîâòîðÿòü îïðåäåëåííûå ïàññàæè.</LI>
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<LI> èòîãå âû ïîëó÷àåòå ãèáêîñòü wav-ôàéëà â ñæàòîì ïîòîêîâîì ôîðìàòå.</LI>
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</UL></BLOCKQUOTE></P>
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<P>×åãî <B>íåò</B> âî FLAC?</P>
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<P><BLOCKQUOTE><UL>
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<LI>FLAC íå îñóùåñòâëÿåò ñæàòèå ñ ïîòåðÿìè. Äëÿ ýòîãî ñóùåñòâóåò ìíîãî õîðîøèõ ôîðìàòîâ, òàêèõ êàê <A HREF="http://www.mp3-tech.org/">mp3</A> (îòëè÷íàÿ ðåàëèçàöèÿ ñ îòêðûòèìè èñõîäíèêàìè <A HREF="http://www.mp3dev.org/mp3/">LAME</A>) è <A HREF="http://www.vorbis.com">Ogg Vorbis</A>.</LI>
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<LI>FLAC íå áóäåò SDMI ñîâìåñòèìûì è ò.ï. Ïåðåä ïðîåêòîì íå ñòîèò öåëè ïîääåðæèâàòü ìåòîäû çàùèòû, êîòîðûå íà ïðàêòèêå ëèøü óâåëè÷èâàþò îáúåì ôàéëà. Êîíå÷íî, ìû íå ñîáèðàåìñÿ ïðåïÿòñòâîâàòü êîìó-ëèáî ñîçäàâàòü ñîîòâåòñòâóþùèå áëîêè ìåòàäàííûõ, îäíàêî, ñòàíäàðòíûå äåêîäåðû âñå ðàâíî áóäóò èõ ïðîïóñêàòü.</LI>
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</UL></BLOCKQUOTE></B>
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<P> Copyright (c) 2001 Josh Coalson</P>
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</BODY>
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