[mythtv-users] HD Resolutions

Michael T. Dean mtdean at thirdcontact.com
Thu May 5 16:58:37 UTC 2011

On 05/05/2011 06:59 AM, Andre wrote:
> On 5 May 2011, at 10:52, Jacob Mansfield wrote:
>> simple question, which is better: 1080i or 720p
> Is there ever a simple question? ;-)
> 720p (at 50 or 60 frames a second) is better for sports due to the higher frame rate.
> 1080p (at 24, 25 or 30 frames a second) is better for movies and drama shot at those low frame rates.

Put another way, 720p and 1080i are "equivalent" formats where 1080i 
trades temporal resolution (frames-per-second) for spatial resolution 
(1920x1080 vs 1280x720), while staying within the same bandwidth 

When encoding video, a given bitrate (and CODEC) can be used to provide 
a given quality of video constrained by image size and frame rate, so 
when you're locked to a bitrate, you can trade pixels or frames to 
maintain image quality.  So, 720p gives you higher temporal resolution 
and lower spatial resolution, but 1080i gives you higher spatial 
resolution and lower temporal resolution.

(To make this easier to understand, it may be useful to consider 1080i 
that has been telecined.  A player than understands how to use inverse 
telecine (ivtc) can re-create the original 1080p24 source from the 
1080i60 signal.  If the broadcast is encoded this way, the 1080i is 
using a lower temporal resolution (24fps), where each frame is 1920x1080 
resolution.  Even when not telecined, 1080i60 has a lower--exactly 
half--temporal resolution than 720p60, which has approximately half the 
spatial resolution.)

This is why the arguments about "fast" versus "slow" moving content.


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