Re: HD, SD, HDMI and aspect ratio questions


"Jomtien" <jomtien@xxxxxxxxx> wrote in message
news:n8skg257q4cmgjq28fcsl57036mf62tnd8@xxxxxxxxxx
Malcolm H wrote:

Although all HD broadcasts have 16:9 aspect ratio, standard definition
(SD)
programmes are broadcast in both 16:9 and 4:3. It is therefore desirable
for
the receiver to switch automatically between 16:9 and 4:3 when SD
programmes
are received.

And they do. But see below.


I am very interested to find out which models of HD receiver connected to
the SkyHD box via HDMI are able to switch aspect ratio automatically when
SD
programmes are being received. This switching is, of course, accomplished
via pin 8 when SCART is used - but SCART and HDMI cannot simultaneously be
used on the same TV input.

The HDMI specification does state that automatic switching is supported
but
I have yet to meet anyone who can demonstrate it to me.

In theory the HDMI/HD spec is entirely widescreen. The source material
should really be all widescreen and any 4:3 content should be
pillar-boxed to 16:9 at source.

As you have noticed the problems arise when you use an HDMI connection
to view SD material which may be 4:3 or W/S. There is no switching
signal built into the HDMI plug so you rely on older non-scart SD
switching like WSS. And not all screens or sources support this.

So it's a toss-up whether there is a switching signal at all, whether
the screen recognises it and indeed whether the screen even permits
you to select 4:3 from an HDMI source. Many don't.

In relation to the Sky HD box, clearly it should pillar-box all 4:3
content when the HMDI connection is in use. This is easy to achieve
and for it to do anything else is silly.


I does not appear that you have read the HDMI specification. It is much more
than just a plug, it is a comprehensive interface definition. The paragraph
stating the Purpose and Scope of the specification is reproduced below.
You will note the words "HDMI can carry high quality multi-channel audio
data and can carry *all* standard and high definition consumer electronics
video formats"

It is therefore incorrect to say that source material should be all
widescreen.
It is absurd to suggest that all 4:3 content should be pillar-boxed at
source. It isn't - and it is unnecessary if the receiver fully complies with
the HDMI specification.

You may study the specification here:

http://www.hdmi.org/download/HDMI_Spec_1.3_GM1.pdf



----------------------
PURPOSE and SCOPE

This document constitutes the specification for the High-Definition
Multimedia Interface (HDMI), version 1.3.

The High-Definition Multimedia Interface is provided for transmitting
digital television audiovisual

signals from DVD players, set-top boxes and other audiovisual sources to
television sets,

projectors and other video displays.

HDMI can carry high quality multi-channel audio data and can carry all
standard and highdefinition

consumer electronics video formats. Content protection technology is
available.

HDMI can also carry control and status information in both directions.

This specification completely describes the interface such that one could
implement a complete

transmission and interconnect solution or any portion of the interface. The
underlying Transition

Minimized Differential Signaling (TMDS)-based protocol and associated
electrical signaling is

described in detail. The mechanical specification of the connector and the
signal placement within

the connector are described.

A device that is compliant with this specification is interoperable with
other compliant devices

through the configuration and implementation provided for in this
specification.

Mechanical, electrical, behavioral and protocol requirements necessary for
compliance are

described for sources, sinks and cables.

-----------------------------




.

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