Win TV Picture Quality
#1
Hi. Looking to set up XMBC and I was thinking about quality of TV picture, and essentially what makes it look good. So you want a good tv tuner card, good cables and a good aerial so that you have a good signal. The signal is then encoded into a file, and stored on a hard drive (even I think live TV - its how you get to pause, rewind, etc).So what I don't understand is what does the encoding? Is it the tv card? Or is the pvr backend? Or is it something you get to pick?

Also (in either case, but I guess especially if its not the tv card) can the encoding calc be done on a gpu?
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#2
In the case of digital TV - it's the broadcaster.

The broadcast signal is encoded to MPEG2 or H264 by the broadcaster (or platform operator). This encoded video is then broadcast digitally, received digitally, and assuming you are using a digital TV capture card (DVB-T, ATSC, DVB-S/S2 etc.) then this stream is either decoded live or recorded to disc (usually exactly as broadcast) and then replayed and decoded on replay. All the tuner card does is tune and demodulate the signal and pass the pre-encoded video and audio (as encoded by the broadcaster) to the PC. No need to encode on the card or the PC. (This is why you can use such low power NAS boxes as TV Headend servers - they literally just have to record or stream the output of the tuner - moving 1s and 0s around untouched)

(There are some network DVB-T/S/S2 tuners that do a decode and recode - but these are mainly aimed at iPhone/iPad type viewing)

The exception to this is if you use a Component or HDMI capture card fed from a set-top box, or an analogue tuner.
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#3
Unless you are old fashioned enough to have analogue TV transmitted to you, the encoding is done by the broadcaster. Then it is transmitted in mpeg2-ts streams. Many streams are muxed into a mux or transport (ie a single frequency carries multiple channels, each channel consisting of a number of streams: video, one or more audio tracks and maybe subtitle tracks).

The tuner simply tunes a frequency and passes all the streams on that frequency [1] to the computer. In the computer software demuxes the streams and saves the ones it wants to hard drive.

So all the encoding is done by the broadcaster, all the tuner/pvr software is doing is remuxing the signal into a new container and saving it to the hard drive.

If you have analogue broadcasts then you need to encode the analogue signal. This can happen in hardware on the tuner card (eg hauppauge pvr-150/250/500 cards encode to mpeg2 in hardware) - many cards don't, and then it is done in software.

[1] Actually some tuners filter the channel you want in hardware and then pass it to the computer, but you don't want that as it removes the ability to record more than one channel per tuner.

noggin beat me to it.
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