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

Andre mythtv-list at dinkum.org.uk
Tue Mar 30 12:23:18 UTC 2010

On 30 Mar 2010, at 12:30, <mythtv at derdev.com> <mythtv at derdev.com> wrote:

> On Tue, 30 Mar 2010 11:46:17 +0100, Andre <mythtv-list at dinkum.org.uk>
> wrote:
>> 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
> Andre, a personal thanks, that was a pretty cool writeup.

No worries, the comment just struck a chord immediately after listening to a lecture given specially to educate broadcast engineers in exactly this stuff.

Glad it was useful to someone, the EBU have many papers and lectures available to the public if you are interested, their stuff is written at quite an accessible level for anyone who can cope with MythTV! You can't get the really good stuff without being a national broadcaster but there's lots of interesting stuff anyone interested can get in return for a registration.

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