There are several ways to convert a digital TV program, or more generally to have a video source TV, in digital format. As you know, have a video audio stream in binary format, ensures reproducibility and copy without any loss of quality as opposed to what happens in the analog recordings on tape, typically VHS. The numerous advantages of digital technology collide, however, with a not insignificant problem: the corruption media, magnetic (HD) or optical (CD, DVD ...) that stores the video may result in the inability to recover it. In contrast to the damage and natural deterioration of a VHS, normally follows a deterioration in the quality that can also be trascurabile.E 'common experience to review a VHS of 10-15 years ago with no obvious problems of aging, it is alas also the common inability to read a CD or DVD burned only 2-3 years earlier. If the average lifetime of optical media stored in a "controlled" can easily exceed 20-30 years, on the contrary is sufficient exposure to the sun for a few minutes (see a CD set on a table near a window) to make the contents of the media is completely unreadable. About the magnetic media is enough to consider how to crash a hard drive is often unexpected, sudden and irreversibile.Tutta ... this premise, only to remember how to take advantage of the benefits of digital without surprises (copy without loss of quality and no deterioration in time), you should plan with intelligence data redundancy: in other words, to recordings of real interest, there should be copies of back-ups that should be checked periodically and replicate.Come I said, there are several ways to digitally record the television and all can be attributed to two types: the digitization of analog TV sources Grab the video and audio streams digitale.Alla first category two families of devices: DVD recorders and Hard Disk "living room" and a number of TV tuner in your computer. About recorders "living room", the most common limits are often for the low quality of the analog signal which together with the limits of certain hardware encoder (which can not compete with the quality of those software), does not always produce high-quality scans; There are of course exceptions, in which filters noise reduction associated with quality encoder scans produce very respectable. The second limitation of digital recorders "living room" it is identified in the editing is not always efficient and immediate use: the rest of the remote was not designed to make editing lineare.La scan on your PC via analogue tuner is made by using one of the many cards (internal or external connected via USB 2.0) for which prices are well below the 100 Euros. The problems associated with the use of such cards, however, are innumerable. First there is the difficulty, often insurmountable, to connect the PC to a power antenna of a type used in the house: the portable antennas to be connected directly to your computer, ensure that receipts are only acceptable in the absence of obstacles, typically in the "open spaces" . The second problem concerns the quality is often inadequate software usually bundled with the card: beyond the quality of these encoder software that should allow you to scan in real time using the often limited resources of the computer calculation, the biggest problem that occurs with almost all of these programs, is the loss of audio sync video on scans of long duration. Normally this problem can be enough to warn of delays or advances the audio of 30-40 ms, ie the time of the two units (1000 ms/50 fps) of a movie interlace: they can do scans of a few tens of minutes to create a mismatch that progressively pass these values \u200b\u200bso as to make the movie unwatchable. These imperfections non è banale poiché, identificato con esattezza il ritardo (cosa tutt'altro che semplice) occorre demultiplexare il flusso audio video e operare con un software di editing sull'audio mediante una filtro di stretching che ne modifica la durata, possibilmente mantenendo inalterata la tonalità. Un software freeware in grado di fare una operazione di stretching sull'audio è VirtualDub : ciò è possibile a partire dalla versione 1.72 mediante l'opzione "use advanced filtering" all'interno del menù audio. Tale operazione è fattibile ma non alla portata di tutti, anche perchè spesso il flusso audio-video è in Mpeg, e dopo il demultiplexing e prima del successivo multiplexing, occorre prevedere una ricompressione dell'audio dopo la sua modifica che ovviamente avviene in formato non compresso. Prossimamente cercherò di realizzare una mini guida per risolvere le problematiche di questo tipo.La causa dello sfasamento tra l'audio e video è dovuta alla errata supposizione da parte del software che la frequenza di digitalizzazione dell'audio e del video siano esattamente quelle impostate. Se ad esempio si digitalizza la TV nel classico formato MPEG PAL, il software presuppone che il video venga digitalizzato con la cadenza di 50 frame al secondo e che l'audio digitalizzato esattamente a 48000 Hz. In realtà in mancanza di un Hardware sulla scheda che verifica e compensa le approssimazioni sul clock, la reale frequenza di campionamento è diversa da quella impostata. Se ad esempio the sound is digitized at 47,970 Hz on average after about a half hour movie, there will be a lag of one secondo.Esistono some software that can keep up the timing by monitoring the actual sampling frequency, so as to identify and then compensate for the phase shifts. For audio, you simply count the samples that the frame grabber provides. Evaluated the error there are two possible ways to solve the problem: we see them soon .. Software as VirtualDub , involved every time you accumulate a phase shift or advance equal to a frame: in the case of PAL video, each 40ms (1000 ms/25 fps), or any errors of 1920 samples of audio at 48000 Hz (48000/25). This error is offset duplicating or removing a frame, a second, respectively, a delay or advance the audio. An opposite approach is realized by software as freeware VirtualVCR operating in real-time audio resampling, interpolation by adding or deleting audio samples so as to compensate for the inaccuracy of the frequency of campionamento.In basis of tests carried out (3 hours of TV Analog to Divx), both mentioned software can guarantee perfect sync, even though both are far from immediate in the choice of parametri.La digitalization of TV with analogue tuner, for some 'time is giving way to grab transmissions DTT (digital terrestrial) and DVB-S (satellite TV). These use the standard video format MPEG 2 (rarely Mpeg1) that can be transferred through software, which is identical bit by bit, on your computer. In reality, the standard transmission of DTT and DVB-S MPEG Stream Trasport involves the use of additional data over the synchronization of various flows, among other things, guarantee the detection of transmission errors. The software that draws the audio stream video, eliminating the additional data, extract the movie, in the absence of transmission errors, is identical to the broadcast: of course the problem of gradual deterioration of the synchronization does not exist. The quality of the transmissions of digital terrestrial and satellite varies according to the "policies" of the sender: a parity bit is available, you can insert a larger number of channels at the expense of quality: the quality of the normally clear the most important channels (Rai, Mediaset, La7 ..) is more than enough though certainly not excellent. In all cases the result is almost always higher than that of an analog TV signal subsequently digitized. The MPEG movie "Grabb" is used without further processing, as well as on your computer, even with the recent DVD players lounge, which are often capable of displaying movies Mpeg 1 and 2 stored on optical media. Through Pc is obviously possible to develop this movie, modify and / or convertirlo.Riguardo quality, should be considered as the bandwidth of a frequency used for digital terrestrial broadcasts is about 24 Mbit / s. It 's so you can send a variable number of channels under the condition that at any moment, the bit rate shall not exceed that value. Assuming that the compression in real time is made from high quality MPEG encoder, in order to ensure a video comparable to that of a good DVD (say about 6 Mbit / s) should not send more than 4 channels per frequency. In fact, if you take a look at the current Italian situation, for each frequency are inserted 6 to 8 channels with a degradation of in some cases also very evident. The growing presence on Italian territory of ADSL high-speed connections, the Internet is making it a simple and immediate viewing and download the TV. This revolution is suffering from an inherent limitation is that the availability of content: on the one hand, we multiply these movies on various video portals (see rai.tv) and an increasing number of "chunks" of video stored on the various video sharing sites ( see Youtube), at present none of the various TV in Italy, offers a service that can provide on request and payment, any transmission of their palinsensto, maybe even the past. The other limitation lies in the difficulty in storing and archiving some movies streamed and protected download: about it is there to say that there are many software that can be overcome, in almost all cases, this obstacle. Regarding the quality of these movies, the need for bandwidth saving and the use of compression codec is not very recent (see the On2 format used in Flash video, FLV) for "tradition" have limited the resolution to 320x240 or classical maximum VideoCD obsolete 352x288 resolution. In the future, surely the quality will tend to improve with the availability of the H.264 codec, will shortly be used with the Flash Player, with megabit bitrate around, able to ensure quality video even at resolutions più elevate quale la 640x480 o la 720x576.Nell'ottica dell'integrazione tra la Televisione e Internet, quella che generalmente viene chiamata IPTV, è da qualche mese on line un servizio di Videoregistrazione Digitale Remota, attualmente in fase beta, proposto dal sito http://www.vcast.it/ sotto il nome di Faucet PVR (Personal Video Recorder). Consiste nella possibilità di richiedere la registrazione di uno o più programmi televisivi in formato digitale indicando canale TV, intervallo di registrazione e formato video: dopo un tempo variabile che dipende dallo stato di carico dei server adibiti al servizio, la registrazione sarà disponibile per il download che potrà avvenire al massimo dopo tre giorni, scaduti i which will be deleted. To access this free service should be registered, declared to be in compliance with the RAI subscription. By your own account (username and password you set during registration) to access to a personal page from which to operate. Let soon
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