{"id":87067,"date":"2020-07-03T07:42:03","date_gmt":"2020-07-03T05:42:03","guid":{"rendered":"https:\/\/prohoster.info\/blog\/administrirovanie\/izuchaem-voip-dvizhok-mediastreamer2-chast-2"},"modified":"2020-07-03T07:42:03","modified_gmt":"2020-07-03T05:42:03","slug":"izuchaem-voip-dvizhok-mediastreamer2-chast-2","status":"publish","type":"post","link":"https:\/\/prohoster.info\/sv\/blog\/administrirovanie\/izuchaem-voip-dvizhok-mediastreamer2-chast-2","title":{"rendered":"Studera VoIP-motorn Mediastreamer2. Del 2","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Artikelmaterialet \u00e4r h\u00e4mtat fr\u00e5n min Zen-kanal<\/a><\/noindex>.<\/p>\n

<\/p>\n

\"Studera<\/p>\n

<\/p>\n

Skapar en tongenerator<\/h2>\n

<\/p>\n

I f\u00f6reg\u00e5ende artikeln<\/a><\/noindex> Vi har installerat mediestr\u00f6mmerbiblioteket, utvecklingsverktygen och kontrollerat deras funktionalitet genom att skapa en testapplikation.<\/p>\n

<\/p>\n

I dag ska vi skapa en applikation som kan generera en tonsignal p\u00e5 ljudkortet. F\u00f6r att l\u00f6sa denna uppgift beh\u00f6ver vi koppla samman filtren i det ljudgenerator-schema som visas nedan:<\/p>\n

<\/p>\n

\"Studera<\/p>\n

<\/a><\/noindex><\/p>\n

Vi l\u00e4ser schemat fr\u00e5n v\u00e4nster till h\u00f6ger, det \u00e4r i detta riktning som v\u00e5r datastream r\u00f6r sig. Pilarna antyder ocks\u00e5 detta. Rektanglarna representerar filter som bearbetar datapaket och visar resultatet p\u00e5 utg\u00e5ngen. Inuti rektangeln anges dess roll och typ av filter med stora bokst\u00e4ver strax under. Pilarna som kopplar samman rektanglarna representerar datak\u00f6er genom vilka datapaket levereras fr\u00e5n filter till filter. Generellt kan det finnas flera ing\u00e5ngar och utg\u00e5ngar f\u00f6r ett filter.<\/p>\n

<\/p>\n

Allt b\u00f6rjar med taktk\u00e4llan som s\u00e4tter tempot f\u00f6r n\u00e4r databehandlingen i filtren sker. Vid varje takt bearbetar varje filter alla datapaket som finns p\u00e5 dess ing\u00e5ng. Och placerar paketen med resultatet p\u00e5 utg\u00e5ngen - i k\u00f6n. F\u00f6rst bearbetar den filter som \u00e4r n\u00e4rmast taktk\u00e4llan, sedan filtren som \u00e4r anslutna till dess utg\u00e5ngar (det kan finnas m\u00e5nga utg\u00e5ngar), och s\u00e5 vidare. N\u00e4r det sista filtret i kedjan har avslutat sin behandling stannar exekveringen tills en ny takt intr\u00e4ffar. Takterna f\u00f6ljer som standard med ett intervall p\u00e5 10 millisekunder. <\/p>\n

<\/p>\n

Vi \u00e5terv\u00e4nder till v\u00e5rt schema. Takt signaler skickas till ing\u00e5ngen av tystnadsk\u00e4llan, det \u00e4r en filter som \u00e4r upptagen med att generera ett datablack med endast nollor vid varje takt. Om vi betraktar detta block som ett block av ljudprover, \u00e4r det inget annat \u00e4n tystnad. Vid f\u00f6rsta anblick kan det verka konstigt att generera datablack med tystnad \u2014 eftersom det inte kan h\u00f6ras, men dessa block \u00e4r n\u00f6dv\u00e4ndiga f\u00f6r att ljudsignalgeneratorn ska fungera. Generatorn anv\u00e4nder dessa block som ett rent papper och skriver in ljudprover i dem. I sitt normala tillst\u00e5nd \u00e4r generatorn avst\u00e4ngd och skickar bara vidare ing\u00e5ngsblocken till utg\u00e5ngen. S\u00e5ledes passerar tystnadsblocken of\u00f6r\u00e4ndrade genom hela schemat fr\u00e5n v\u00e4nster till h\u00f6ger, vilket n\u00e5r ljudkortet. Som tyst h\u00e4mtar ljudkortet block fr\u00e5n k\u00f6en ansluten till sin ing\u00e5ng.<\/p>\n

<\/p>\n

Men allt f\u00f6r\u00e4ndras om generatorn f\u00e5r kommando att spela upp ljud, den b\u00f6rjar generera ljudprover och ers\u00e4tter dem i ing\u00e5ngsblocken samt skickar de \u00e4ndrade blocken till utg\u00e5ngen. Ljudkortet b\u00f6rjar spela upp ljudet. Nedan f\u00f6ljer programmet som implementerar det beskrivna arbetsschemat:<\/p>\n

<\/p>\n

\/* \u0424\u0430\u0439\u043b mstest2.c *\/\n#include <mediastreamer2\/msfilter.h>\n#include <mediastreamer2\/msticker.h>\n#include <mediastreamer2\/dtmfgen.h>\n#include <mediastreamer2\/mssndcard.h>\nint main()\n{\n    ms_init();\n\n    \/* \u0421\u043e\u0437\u0434\u0430\u0435\u043c \u044d\u043a\u0437\u0435\u043c\u043f\u043b\u044f\u0440\u044b \u0444\u0438\u043b\u044c\u0442\u0440\u043e\u0432. *\/\n    MSFilter  *voidsource = ms_filter_new(MS_VOID_SOURCE_ID);\n    MSFilter  *dtmfgen = ms_filter_new(MS_DTMF_GEN_ID);\n    MSSndCard *card_playback = ms_snd_card_manager_get_default_card(ms_snd_card_manager_get());\n    MSFilter  *snd_card_write = ms_snd_card_create_writer(card_playback);\n\n    \/* \u0421\u043e\u0437\u0434\u0430\u0435\u043c \u0442\u0438\u043a\u0435\u0440. *\/\n    MSTicker *ticker = ms_ticker_new();\n\n    \/* \u0421\u043e\u0435\u0434\u0438\u043d\u044f\u0435\u043c \u0444\u0438\u043b\u044c\u0442\u0440\u044b \u0432 \u0446\u0435\u043f\u043e\u0447\u043a\u0443. *\/\n    ms_filter_link(voidsource, 0, dtmfgen, 0);\n    ms_filter_link(dtmfgen, 0, snd_card_write, 0);\n\n   \/* \u041f\u043e\u0434\u043a\u043b\u044e\u0447\u0430\u0435\u043c \u0438\u0441\u0442\u043e\u0447\u043d\u0438\u043a \u0442\u0430\u043a\u0442\u043e\u0432. *\/\n   ms_ticker_attach(ticker, voidsource);\n\n   \/* \u0412\u043a\u043b\u044e\u0447\u0430\u0435\u043c \u0437\u0432\u0443\u043a\u043e\u0432\u043e\u0439 \u0433\u0435\u043d\u0435\u0440\u0430\u0442\u043e\u0440. *\/\n   char key='1';\n   ms_filter_call_method(dtmfgen, MS_DTMF_GEN_PLAY, (void*)&key);\n\n   \/* \u0414\u0430\u0435\u043c, \u0432\u0440\u0435\u043c\u044f, \u0447\u0442\u043e\u0431\u044b \u0432\u0441\u0435 \u0431\u043b\u043e\u043a\u0438 \u0434\u0430\u043d\u043d\u044b\u0445 \u0431\u044b\u043b\u0438 \u043f\u043e\u043b\u0443\u0447\u0435\u043d\u044b \u0437\u0432\u0443\u043a\u043e\u0432\u043e\u0439 \u043a\u0430\u0440\u0442\u043e\u0439.*\/\n   ms_sleep(2);   \n}<\/code><\/pre>\n
<\/p>\n
Efter initialisering av mediastreamern, skapas tre filter: voidsource, dtmfgen, snd_card_write<\/em>. En k\u00e4llkod f\u00f6r taktsignalen skapas.<\/p>\n
<\/p>\n
D\u00e4refter m\u00e5ste vi utf\u00f6ra anslutningen av filtren enligt v\u00e5rt schema, d\u00e4r k\u00e4llan f\u00f6r klockan ska kopplas in sist, eftersom schemat omedelbart b\u00f6rjar arbeta efter detta. Om k\u00e4llan f\u00f6r klockan kopplas till ett ofullst\u00e4ndigt schema kan det h\u00e4nda att mediastreamern avslutas ov\u00e4ntat, om den uppt\u00e4cker att det finns minst ett filter i kedjan vars alla ing\u00e5ngar eller alla utg\u00e5ngar \"h\u00e4nger i luften\" (inte anslutna). <\/p>\n
<\/p>\n
Anslutningen av filtren sker med hj\u00e4lp av funktionen <\/p>\n
<\/p>\n
ms_filter_link(src, src_out, dst, dst_in)<\/code><\/pre>\n
<\/p>\n
d\u00e4r den f\u00f6rsta argumentet \u00e4r en pekare till k\u00e4llfilter, den andra argumentet \u2014 k\u00e4llans utg\u00e5ngsnr (observera att ing\u00e5ngar och utg\u00e5ngar numreras fr\u00e5n noll). Den tredje argumentet \u00e4r en pekare till mottagarfilter, den fj\u00e4rde \u2014 ing\u00e5ngens nr av mottagaren.<\/p>\n
<\/p>\n
Alla filter \u00e4r kopplade och den sista ansluts till klockk\u00e4llan (h\u00e4danefter kallar vi den bara f\u00f6r tickern). D\u00e4refter aktiveras v\u00e5rt ljudschema, men i datorns h\u00f6gtalare h\u00f6rs fortfarande ingenting \u2014 ljudgeneratorn \u00e4r avst\u00e4ngd och sl\u00e4pper bara igenom ing\u00e5ngsdatablock med tystnad. F\u00f6r att starta generationen av en tonsignal m\u00e5ste filtermetoden f\u00f6r generatorn anropas.<\/p>\n
<\/p>\n
Vi kommer att generera en tv\u00e5tonssignal (DTMF) som motsvarar knapptryckningen p\u00e5 telefonens knap \"1\". F\u00f6r detta anv\u00e4nder vi en funktion ms_filter_call_method()<\/em> f\u00f6r att anropa metoden MS_DTMF_GEN_PLAY, och skicka en pekare till koden som signalen ska motsvara som argument.<\/p>\n
<\/p>\n
Nu \u00e5terst\u00e5r det att kompilera programmet:<\/p>\n
<\/p>\n
$ gcc mstest2.c -o mstest2 `pkg-config mediastreamer --libs --cflags`<\/code><\/pre>\n
<\/p>\n
Och k\u00f6ra:<\/p>\n
<\/p>\n
$ .\/mstest2<\/code><\/pre>\n
<\/p>\n
N\u00e4r programmet k\u00f6rs kommer du att h\u00f6ra ett kort ljudsignal i datorns h\u00f6gtalare som best\u00e5r av tv\u00e5 toner.<\/p>\n
<\/p>\n
Vi har byggt och startat v\u00e5rt f\u00f6rsta ljudschema. Vi s\u00e5g hur man skapar instanser av filter, hur man kopplar dem och hur man anropar deras metoder. Efter att ha gl\u00e4djats \u00e5t v\u00e5r f\u00f6rsta framg\u00e5ng m\u00e5ste vi \u00e4nd\u00e5 l\u00e4gga m\u00e4rke till att v\u00e5rt program inte frig\u00f6r minne innan det avslutas. I n\u00e4sta artikeln<\/a><\/noindex> del kommer vi att l\u00e4ra oss att st\u00e4da upp efter oss.<\/p>\n
K\u00e4lla: habr.com<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"
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