[opendtv] Re: Popular screen aspect ratios

  • From: Ron Economos <w6rz@xxxxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Tue, 11 Jan 2011 05:43:37 -0800

Take a look at section 6.3.3 in H.262.

***************************************************************************
If sequence_display_extension() is not present, then it is intended
that the entire reconstructed frame is intended to be mapped to the
entire active region of the display. The sample aspect ratio may be
calculated as follows:

SAR = DAR × horizontal_size / vertical_size

NOTE 1 – In this case horizontal_size and vertical_size are
constrained by the SAR of the source and the DAR selected.

If sequence_display_extension() is present then the sample aspect
ratio may be calculated as follows:

SAR = DAR × display_horizontal_size / display_vertical_size
***************************************************************************

The SAR of a 720x480 stream with aspect_ratio_information
set to 16:9 and sequence_display_extension() NOT present
is 0.84375.

The SAR of a 720x480 stream with aspect_ratio_information
set to 4:3, sequence_display_extension() present,
display_horizontal_size = 540 and display_vertical_size = 480
is 0.84375.

Clearly, they are equivalent. The equation in the DVB specification
is just restating this section in H.262

Ron

On 1/11/2011 3:40 AM, Craig Birkmaier wrote:
I see nothing in the MPEG-2 standard to suggest that this is a trick way to define a 16:9 source image. 





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