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How Windows manages playing multimedia

Win­dows auto­mat­ic behaviour

Quando un file viene giocato su Win-dows, most play­er soft­ware simply lets Win­dows handle the play­back (Media Play­er Clas­sic Home Cinema is an excep­tion).  Win­dows auto­mat­ic­ally selects an appro­pri­ate split­ter to “split” the con­tain­er, and then selects the appro­pri­ate decoders to decode each of the streams. Each decoded stream is then sent to a final stage known as a ren­der­er. The split­ter, decoders and ren­der­ers are known as fil­ters and are some­times referred to as codecs. The term codec has sev­er­al com­mon uses, but is gen­er­ally used to mean a pro­gram which can carry out either encod­ing or decod­ing. In this guide we will use the term codec to refer to com­plete soft­ware pack­ages, which may con­tain mul­tiple fil­ters and sup­port mul­tiple stream types. Each fil­ter is a self-con­tained unit, usu­ally stored inside an .ax file in the system32 folder. The pro­cess of select­ing the split­ter, decoders and ren­der­ers is known as build­ing a graph. There are util­it­ies avail­able which allow you to see what graphs Win­dows will build for a par­tic­u­lar file, così come la costruzione grafici personalizzati per provare la riproduzione


Ren-der-tori sono la fase finale del grafico; e sono l'interfaccia tra i flussi decodificati e l'hardware che emette il flusso - per esempio i driver della scheda video, or the sound card drivers. They man­age the way the out­put fits into the Win­dows sys­tem. So for example you may play back a video in a win­dow (al contrario di schermo intero) and also have anoth­er pro­gram open. Win­dows needs to how big to dis­play the video, and where on the screen. You may also move anoth­er pro­gram or win­dow par­tially in front of the video and Win­dows needs to know to dis­card this part of the video. This is all man­aged by the renderers.

Decodifica Hard-ware

Il suo-tor-ic-alleato tutti decodifica-zione è stata fatta dal CPU.  Il CPU è progettato per essere molto flessi-bile, che significa che può sotto-prendere qualsiasi operazione, but is not espe­cially effi­cient at any­thing. The increase in HD video con­tent which requires sub­stan­tial pro­cessing to decode has led to a demand for more effi­cient video decod­ing hard­ware. All mod­ern video cards now include some level of “hard­ware decod­ing” of the 3 BluRay nor-me-zione ENCOD (mpeg2, h.264, VC1).  The level of sup­port var­ies but with each new gen­er­a­tion of hard­ware more stand­ards are sup­por­ted. The latest gen­er­a­tion of CPUs from Intel now also include ded­ic­ated decod­ing hard­ware which frees the main parts of the CPU for oth­er tasks, and reduces power con­sump­tion. Ded­ic­ated GPU e CPU hard­ware decod­ing can only be util­ised if the codec used for decod­ing sup­ports hard­ware decod­ing. The level of sup­port for this fea­ture is vari­able, ma è crescere-ing, and sev­er­al of the free codecs provide good sup­port. The codecs Microsoft provides with Win­dows also offer some sup­port. The sys­tem of hard­ware accel­er­a­tion is com­monly known as DXVA (-A-zione Accel-er Dir-ECTX Video).  Molti recenti decoder hardware dedicati supportano anche le varie caratteristiche ottimizzazione delle immagini.

In molti casi, decodifica hardware non è compatibile con l'uso di sottotitoli, how-mai, DXVA con sottotitoli è possibile tramite il libero open-source ffdshow tryouts.

Stream output Raw

In some cases no decoder is required. Some audio on BluRay disks is uncom­pressed and can be sent dir­ectly from the split­ter to the ren­der­er without need of a decoder. In addi­tion to this, many home theatre amp­li­fi­ers include digit­al con­nect­ors (SPDIF o HDMI) e hanno i propri decoder hardware per l' 2 piombo-zione sistemi: Dolby and DTS. If you have an amp­li­fi­er which sup­ports hard­ware decod­ing you may wish to leave the audio stream encoded and send the encoded stream to the amp­li­fi­er for decod­ing. To do this the stream from the split­ter must be sent to the appro­pri­ate hard­ware (sia una scheda audio nel caso di SPDIF, o la scheda video HDMI).  This stream must be sent in the cor­rect way so the hard­ware knows to out­put it over the digit­al con­nec­tion. To do this still requires a fil­ter, but the fil­ter will not decode the stream. The most com­mon codec used for this pur­pose is called ac3filter.

Video is nev­er nor­mally raw and so always requires a decoder fil­ter. It must also pass through the ren­der­er. Sub­title inform­a­tion is also passed to the ren­der­er for ren­der­ing on top of the video.

Nuovo codec sistema in Vista

The sys­tem Win­dows uses to man­age all these fil­ters is called Dir­ect­Show. The vast major­ity of fil­ters are designed to con­form to the Dir­ect­Show stand­ards. How­ever, sotto Windows Vista, Microsoft intro­duced a new sys­tem called Media Found­a­tion. This new sys­tem runs in par­al­lel with Dir­ect­Show, but takes pre­ced­ence. Microsoft has include Media Found­a­tion codecs in all Win­dows releases since Vista, e quando un file viene riprodotto, Win­dows will try to use the Media Found­a­tion codecs to play­back the file. This has made it more dif­fi­cult to use altern­at­ive codecs.

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