Nice explanation of Digital vs analog OTA tuning

[Jarod Wilson]

On Feb 14, 2007, at 12:12, Ben Scott wrote:

> On 2/14/07, Jon 'maddog' Hall <maddog at li.org> wrote:
>> http://crave.cnet.com/8301-1_105-9685948-1.html?tag=nl.e501
>
>  Good link.  Thanks.
>
>  There's also the GNHLUG wiki page, which has a table which explains
> what can work with MythTV, along with links.  (Full disclosure: I
> wrote a big chunk of said page.)
>
> http://wiki.gnhlug.org/twiki2/bin/view/Www/MythTV
>
>  It is important to realize that "Digital TV" and "High Definition
> TV" are not synonymous.  All high def is digital, but not all digital
> is high def.  Digital TV (DTV) can and is used to send plain old
> standard definition TV programming.

Note that digital sdtv stations are actually sometimes a bit better  
than the analog versions, as they can be sent in a progressive-scan  
format (720x480p) rather than only traditional interlaced (720x480i).


>  Likewise, HDTV is not synonymous with "pay TV".  Local stations are
> already broadcasting OTA (over-the-air) in digital, and much of it in
> high definition, for "free".  The picture quality can sometimes even
> be higher than cable.

Important to note the distinction between an mpeg2 transport stream  
(mpeg2-ts) and an mpeg2 program stream (mpeg2-ps) here. An mpeg2-ts  
can contain multiple mpeg2-ps's (think of a ps as a pairing of one  
video stream and one audio stream or a sub-channel of the main  
channel). OTA broadcasters usually doesn't mess with the mpeg2-ts at  
all, they send the whole enchilada, and its up the tuner to decide  
which ps/sub-channel to watch (Myth handles this fairly  
transparently). The cable company usually breaks the original mpeg2- 
ts down and only sends a single program stream per channel, but its  
typically the exact same mpeg2-ps that you ultimately end up  
watching, regardless of cable or OTA. There are very rare cases of  
providers who do muck with the program stream further, scaling it  
down in resolution or what have you, but that's fairly rare.

-- 
Jarod Wilson
jarod at wilsonet.com


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