[mythtv-users] Graphic cards supporting VDPAU and sound over HDMI

[Andre]

On 30 Mar 2010, at 11:18, Christopher Kerr wrote:
> 
> Actually, that reminds me of something I've been wondering about for a
> while: why do we use 1080i anyway? Basically all HD displays are
> progressive by nature, and it takes the same amount of bandwidth to
> broadcast 1080i50 as 1080p25. So why do they do it that way? Doesn't
> MPEG-2 encoding work more efficiently on progressive content, anyhow?


Yes, yes and yes!

When HD first started commercially (theoretically it's 20+ years old already) in the US you could buy 720p60 and 1080i30 equipment. In Europe only 1080i25 for many years, even now lots of equipment needs firmware updates to work properly with 720p50 or doesn't ever work properly!  So in the US there are some stations that transmit 720p and some sports events are shot in 720p, no-one would shoot anything live in 1080p25 or 1080p30, it would look truly awful. Drama and other shows where everything can be controlled very thoroughly especially the camera movements often shoot in 1080p25 or 1080p24, actually more often 2k24 or on film.

It's pretty much impossible to change a TV station from 720p50 to 1080i25 or 1080p25 between programmes, on outside broadcasts it can take a day to switch everything over in just one truck. So 1080i25 gives a compromise between ok 1080p25 for movies and 1080i25 for live sports without changing anything. Some transmission encoders will detect 1080p25 shows in a 1080i25 feed, de-interlace and transmit 1080p25. Just search the lists here for people having trouble with "progressive flag" video playback in MythTV.

Things are changing though an EBU lecture yesterday referred to interlaced video as "legacy HD", all the new HD standards do not permit interlaced video :-))

Most broadcast engineers don't really understand compressed video, very few understand that 720p actually has slightly higher detail than 1080i, very very few will believe your assertion that 1080p25 takes the same bandwidth as 1080i25 (in fact it needs less) the administrators are worse and most of the viewers have no concept! Many many stations launch with 1080i because the numbers are bigger and that's what our viewers want, I hear this so much of the time.

When broadcast TV stations talk about 1080p they usually mean 1080p50 or 1080p60, equipment to do this is currently very expensive, and almost no-one knows how to work with it. In time it will come, it looks utterly gorgeous and doesn't need any more transmission bandwidth than 1080i25, in many cases it uses less, try finding a broadcast engineer that believes that!

Sorry too much information ;-)

Andre