Preston Crow wrote:
Would some of you mind offering a little info about ATSC/DVB?
I've done a bit of reading and understand there basically just two different
standards. A message on another mailing list mentioned that DVB was a
European standard and ATSC was in the US. But, while browsing a web site
that listed free satellite channels in the US most listed their video type
as DVB. I live in the southern US. What kind of equipment should I be
looking for? I'm a bit new to this. At present all I own is a 12 year old
19 inch portable TV with rabbit ears. No cable or satellite so I need basic
info if I'm going to build a high definition PVR. You guys at mythtv seem
quite knowledgeable. Hope you don't mind sharing.
Yes, it's confusing. DVB stands for "digital video broadcasting," I
think. ATSC is the American standard for broadcasting digital
television--think of it as the digital version of NTSC. Europe uses a
different standard for digital TV that is commonly known as DVB (even
though ATSC is a form of digital video broadcasting).
Correct. DVB is not only used in Europe though - AFAIK Australia use it and parts of Asia and South America, probably some other places too.
Let me expand a bit on the technical details. It helps to think of it in different layers:
First there's the "transport" layer which basically deals with sending data bits from the TV station to you. With DVB there are three big broadcast methods (terrestrial, cable and satellite) and hence three "substandards" (DVB-T, DVB-C & DVB-S). They use different antennas (obviously), different frequencies and also different signal modulations so the tuners are normally not compatible. I don't know exactly how this works in ATSC land but I think ATSC uses different modulations from DVB so ATSC tuners are probably not compatible with DVB tuners.
Second layer, let's call it the "MPEG" layer. This deals with the format of the bitstream that was received from the transport layer, and as far as I know this is more or less identical between DVB-* & ATSC, since the data is sent according to the MPEG spec. The bitstream contains one or more audio & video streams from one or more tv/radio stations, multiplexed into a single transport stream (TS). The video can be standard definition (SD) or high definition (HD) with different resolutions and aspect ratios and there are also several audio formats. I think ATSC happens to use only HDTV video and AC3 audio (and that's why confused Americans say "HDTV" when they really mean ATSC), but that is just a small subset of what the MPEG platform allows. The TS format is not the same as the format used on DVDs, but it is similar (part of the same spec). DVDs use MPEG "program stream" (PS) format and the DVB recorder in Myth can do an on-the-fly conversion to PS before saving the data, but the code is a bit dirty and doesn't produce 100% valid PS data so in many ways it's better to record the pure TS data.
Third layer, the "meta data" that is also injected into the TS, for example: network information, channel listings, tv guide data and so on. This is called SI (Service Information) for DVB and I think with ATSC it's called PSIP. ATSC and DVB have some similarities here but much of it is incompatible due to different data formats. Myth can parse both DVB & ATSC style though so it's no big deal.
There you have it! I hope I got it somewhat right at least... :-)
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