[mythtvnz] Recording Live Earth for 22 hours
Steve Hodge
mythtvnz@lists.linuxnut.co.nz
Mon, 9 Jul 2007 22:46:04 +1200
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On 7/9/07, Jason Haar <jhaar-ourshack-com@whanau.org> wrote:Hmmm, so PAL is
47GBytes and widescreen is 65GBytes... Is "widescreen"
> HD?
No. HDTV is a specific standard that no one is in NZ is using. It involves a
bunch of standard resolutions, most of them higher than "SD" or PAL
resolution. See http://en.wikipedia.org/wiki/High-definition_television for
details. There is talk about Freeview going to widescreen for terrestrial
DVB (DVB-T) sometime in the next couple of years and Sky have also said they
might go to HD in 2008, but no one has announced anything concrete AFAIK.
There is actually no difference in NZ between a regular 4:3 broadcast and
widescreen broadcast: they're both standard PAL signals at standard PAL
resolutions. (Though I think I heard that Sky were broadcasting some
channels in lower resolutions, but I haven't checked myself). The only
difference is that the widescreen picture is squashed horizontally
(anamorphic - see http://en.wikipedia.org/wiki/Anamorphic_widescreen).
If so, doesn't that mean there must be massive "compression" (i.e.
> loss) for the two to be so relatively similar in size?
>
We don't have enough info to know why the difference is what is in this
case. Simon was recording using an analogue capture card which will be
running at the resolution and bitrate it is set for (which has nothing to do
with the resolution and bitrate of the broadcast signal). His settings may
be optimal for the signal, but they probably aren't - the true resolution of
the signal could have been higher or lower. Steve was using a DVB-S card so
he's got the recording exactly as it was broadcast - his file size reflects
the bitrate of the satellite broadcast, which is not necessarily the same as
broadcast Sky made.
So yes, you could say that the widescreen signal is compressed compared to
the non-widescreen signal since the same horizontal resolution is used to
show more picture. But in practice horizontal resolution is no where near as
important as veritcal resolution, which is partly why NTSC and PAL are
defined in terms of the number of lines in the picture, why the HDTV
resolutions are known by their vertical resolution, and why anamorphic
widescreen works at all given the low resolution it's working with (the
effective horizontal resolution of SD signals through composite cables is
much less than 480 pixels - probably more like 320).
Cheers,
Steve
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On 7/9/07, <b class="gmail_sendername">Jason Haar</b> <<a href="mailto:jhaar-ourshack-com@whanau.org">jhaar-ourshack-com@whanau.org</a>> wrote:<div><span class="gmail_quote"></span>Hmmm, so PAL is 47GBytes and widescreen is 65GBytes... Is "widescreen"
<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">HD?</blockquote><div><br>No. HDTV is a specific standard that no one is in NZ is using. It involves a bunch of standard resolutions, most of them higher than "SD" or PAL resolution. See
<a href="http://en.wikipedia.org/wiki/High-definition_television">http://en.wikipedia.org/wiki/High-definition_television</a> for details. There is talk about Freeview going to widescreen for terrestrial DVB (DVB-T) sometime in the next couple of years and Sky have also said they might go to HD in 2008, but no one has announced anything concrete AFAIK.
<br><br>There is actually no difference in NZ between a regular 4:3 broadcast and widescreen broadcast: they're both standard PAL signals at standard PAL resolutions. (Though I think I heard that Sky were broadcasting some channels in lower resolutions, but I haven't checked myself). The only difference is that the widescreen picture is squashed horizontally (anamorphic - see
<a href="http://en.wikipedia.org/wiki/Anamorphic_widescreen">http://en.wikipedia.org/wiki/Anamorphic_widescreen</a>).<br></div><br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
If so, doesn't that mean there must be massive "compression" (i.e.<br>loss) for the two to be so relatively similar in size?<br></blockquote></div><br>We don't have enough info to know why the difference is what is in this case. Simon was recording using an analogue capture card which will be running at the resolution and bitrate it is set for (which has nothing to do with the resolution and bitrate of the broadcast signal). His settings may be optimal for the signal, but they probably aren't - the true resolution of the signal could have been higher or lower. Steve was using a DVB-S card so he's got the recording exactly as it was broadcast - his file size reflects the bitrate of the satellite broadcast, which is not necessarily the same as broadcast Sky made.
<br><br>So yes, you could say that the widescreen signal is compressed compared to the non-widescreen signal since the same horizontal resolution is used to show more picture. But in practice horizontal resolution is no where near as important as veritcal resolution, which is partly why NTSC and PAL are defined in terms of the number of lines in the picture, why the HDTV resolutions are known by their vertical resolution, and why anamorphic widescreen works at all given the low resolution it's working with (the effective horizontal resolution of SD signals through composite cables is much less than 480 pixels - probably more like 320).
<br><br>Cheers,<br>Steve<br>
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