[opendtv] Re: Popular screen aspect ratios

  • From: Ron Economos <w6rz@xxxxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Mon, 10 Jan 2011 09:34:50 -0800

Here's the text of the original question:

If a 720x480 MPEG-2 video bitstream with
aspect_ratio_information set to 4:3,
display_horizontal_size set to 540 and
display_vertical_size set to 480 is received
by a decoder, how should it display the
image on a 16:9 output?

In the DVB specification, there's an equation:

display_horizontal_size = 4 / 3 * horizontal_size / source aspect ratio

For 2.21:1 source aspect ratio, display_horizontal_size would
be 434.

Ron

On 1/10/2011 5:27 AM, John Shutt wrote:
Not a fair question, Ron, because you never stated aspect_ratio_information. Are decoders to automatically infer that if the display_horizontal_size is smaller than the horizontal_size, that the source material is always 16:9? What if the source material were 2.21:1, also allowed under 5.1.3? 

John


----- Original Message ----- From: "Ron Economos" <w6rz@xxxxxxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
Sent: Saturday, January 08, 2011 7:19 AM
Subject: [opendtv] Re: Popular screen aspect ratios



It's a trick question. It's just a good example of the
complexity associated with digital video aspect ratios.

The answer is that the decoder display process
(when set for 16:9 output) should just consider it
to be a 16:9 image and not perform any scaling
or cropping at all.

A specification that discusses this is here:
http://www.etsi.org/deliver/etsi_tr/101100_101199/101154/01.04.01_60/tr_101154v010401p.pdf 

See section 5.1.3






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