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| <CENTER><H2>FLAC: õàðàêòåðèñòèêè</H2></CENTER> |
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| <P>FLAC - ýòî àááðåâèàòóðà îò Free Lossless Audio Codec (ñâîáîäíûé àóäèîêîäåê, ñæèìàþùèé áåç ïîòåðü). Ïðîåêò FLAC âêëþ÷àåò:</P> |
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| <LI>ïîòîêîâûé ôîðìàò;</LI> |
| <LI>áàçîâûå êîäåðû è äåêîäåðû â âèäå áèáëèîòåê;</LI> |
| <LI><B><TT>flac</TT></B>, óòèëèòó êîìàíäíîé ñòðîêè, âûïîëíÿþùóþ ñæàòèå è ðàñïàêîâêó ôàéëîâ .flac;</LI> |
| <LI><B><TT>metaflac</TT></B>, óòèëèòó êîìàíäíîé ñòðîêè äëÿ ðåäàêòèðîâàíèÿ ìåòàäàííûõ â ôàéëàõ .flac;</LI> |
| <LI>ïëàãèíû äëÿ ðàçíûõ ïëåéåðîâ.</LI> |
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| <P>"Ñâîáîäà" îçíà÷àåò, ÷òî ñïåöèôèêàöèÿ ïîòîêîâîãî ôîðìàòà îòêðûòà äëÿ âñåõ è ìîæåò áûòü èñïîëüçîâàíà äëÿ ëþáûõ öåëåé (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 âñå èñõîäíûå òåêñòû äîñòóïíû ïî ëèöåíçèÿì, îáÿçûâàþùèì ïðåäîñòàâëÿòü èñõîäíûå êîäû.</P> |
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| <P>FLAC êîìïèëèðóåòñÿ íà ìíîæåñòâå ïëàòôîðì: Unixes (Linux, *BSD, Solaris, OS X), Windows, BeOS è OS/2. Èìåþòñÿ ñèñòåìû ñáîðêè äëÿ autoconf/automake, MSVC, Watcom C è Project Builder.</P> |
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| <P>Õàðàêòåðèñòèêè FLAC:</P> |
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| <LI>Ôîðìàò FLAC è ìåòîäû êîäèðîâàíèÿ/äåêîäèðîâàíèÿ íå çàùèùåíû ïàòåíòàìè.</LI> |
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| <LI><B>Ñæàòèå áåç ïîòåðü</B>: Êîäèðîâàíèå PCM äàííûõ íå ïðèâîäèò ê ïîòåðå èíôîðìàöèè, ñëåäîâàòåëüíî äåêîäèðóåìûé àóäèîôàéë àáñîëþòíî èäåíòè÷åí òîìó, êîòîðûé áûë ïîäàí íà âõîä êîäåðó. ×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><B>Ñêîðîñòü</B>: Ñêîðîñòü ðàáîòû ïðè êîäèðîâàíèè è äåêîäèðîâàíèè íåñèììåòðè÷íû. Äëÿ äåêîäèðîâàíèÿ èñïîëüçóåòñÿ òîëüêî öåëî÷èñëåííàÿ àðèôìåòèêà, êîòîðàÿ òðåáóåò çíà÷èòåëüíî ìåíüøå âû÷èñëåíèé, ÷åì â ïåðöåïöèîííûõ êîäåêàõ. Äåêîäèðîâàíèå â ðåàëüíîì âðåìåíè ëåãêî äîñòèæèìî äàæå íà ñòàðûõ êîìïüþòåðàõ.</LI> |
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| <LI><B>Àïïàðàòíàÿ ïîääåðæêà</B>: Áëàãîäàðÿ ñâîáîäíîé áàçîâîé ðåàëèçàöèè è ïðîñòîìó äåêîäèðîâàíèþ FLAC ÿâëÿåòñÿ åäèíñòâåííûì àóäèîêîäåêîì, ñæèìàþùèì áåç ïîòåðü, êîòîðûé èìååò àïïàðàòíóþ ïîääåðæêó.</LI> |
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| <LI><B>Ïîòî÷íîñòü</B>: Êàæäûé ôðåéì FLAC 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><B>Ïîèñê</B>: 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><B>Ìåòàäàííûå</B>: FLAC èìååò ðàñøèðÿåìóþ ñèñòåìó ìåòàäàííûõ. Íîâûå áëîêè ìåòàäàííûõ ìîãóò áûòü îïðåäåëåíû è ðåàëèçîâàíû â áóäóùèõ âåðñèÿõ áåç ïîòåðè îáðàòíîé ñîâìåñòèìîñòè. Ñåé÷àñ îïðåäåëåíû òèïû ìåòàäàííûõ äëÿ òàáëèö ïîèñêà, òåãîâ è ñïèñêîâ ðàçìåòêè àóäèîäèñêîâ. Ïðèëîæåíèå ìîæåò èñïîëüçîâàòü áëîê ìåòàäàííûõ <A HREF="format.html#def_APPLICATION"><TT>APPLICATION</TT></A> ïîñëå ðåãèñòðàöèè äëÿ íåãî <A HREF="id.html">ID</A>.</LI> |
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| <LI><B>Àðõèâèðîâàíèå</B>: FLAC óäîáíî èñïîëüçîâàòü äëÿ àðõèâàöèè, òàê êàê ñæàòèå ñ åãî ïîìîùüþ íå ïðèâîäèò ê ïîòåðå èíôîðìàöèè. 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, êîäåð ïðåêðàùàåò ðàáîòó.</LI> |
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| <LI><B>Àðõèâèðîâàíèå àóäèîäèñêîâ</B>: Ó FLAC åñëè áëîê ìåòàäàííûõ <TT>CUESHEET</TT>, â êîòîðîì ñîõðàíÿåòñÿ òàáëèöà ðàçìåòêè àóäèîäèñêà. Íàïðèìåð, ìîæíî çàïèñàòü àóäèîäèñê â îäèí ôàéë, à çàòåì èìïîðòèðîâàòü åãî òàáëèöó ðàçìåòêè ïðè êîäèðîâàíèè, ÷òîáû ïîëó÷åííûé ôàéë èìåë òàêîå æå ïðåäñòàâëåíèå êàê è äèñê. Åñëè îðèãèíàë àóäèîäèñêà áóäåò èñïîð÷åí, òî âû ñìîæåòå âîññòàíîâèòü òàáëèöó ðàçìåòêè, ÷òîáû çàïèñàòü òî÷íóþ êîïèþ äèñêà.</LI> |
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| <LI><B>Óñòîé÷èâîñòü îò îøèáîê</B>: Áëàãîäàðÿ ðàçáèåíèþ íà ôðåéìû, îøèáêè â ïîòîêå ëîêàëèçóþòñÿ äî óðîâíÿ ôðåéìà, â êîòîðîì ïðîèçîøëà îøèáêà (îáû÷íî íåñêîëüêî ñîòûõ ñåêóíäû).  íåêîòîðûõ êîäåêàõ îäíà îøèáêà ìîæåò ïðèâåñòè ê ïîòåðå âñåãî îñòàòêà ïîòîêà.</LI> |
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| <P>×åãî <B>íåò</B> âî FLAC?</P> |
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| <LI>FLAC íå îñóùåñòâëÿåò ñæàòèå ñ ïîòåðÿìè. Äëÿ ýòîãî ñóùåñòâóåò ìíîãî õîðîøèõ ôîðìàòîâ, òàêèõ êàê <A HREF="http://www.vorbis.com">Vorbis</A>, <A HREF="http://musepack.org/">MPC</A> è <A HREF="http://www.mp3-tech.org/">mp3</A> (îòëè÷íàÿ ðåàëèçàöèÿ ñ îòêðûòèìè èñõîäíûìè òåêñòàìè <A HREF="http://www.mp3dev.org/mp3/">LAME</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 ñìîæåì ïðåïÿòñòâîâàòü êîìó-ëèáî ñîçäàâàòü íåñâîáîäíûå áëîêè ìåòàäàííûõ, îäíàêî, ñòàíäàðòíûå äåêîäåðû âñå ðàâíî áóäóò èõ ïðîïóñêàòü.</LI> |
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