[opendtv] Re: Print Story: European broadcasters focus on improved TV picture on Yahoo! New
- From: "John Shutt" <shuttj@xxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Tue, 7 Jun 2005 16:46:04 -0400
Bert,
You are high on you MPEG 2 SD bit requirement, as determined by our own real
world testing. We have determined that 2.5 is the minimum bitrate for MPEG
2 SD. 4 Mbps gives you pristine video. 5 Mbps is desirable but overkill
for most applications.
17 Mbps is the most you can allocate to video in ATSC, in order to leave
room for audio and PSIP data. Again, with our own real world testing, we
find that 720p 60 looks fine at about 12-14 Mbps. It is dog food at 10
Mbps. There appears to be a cliff edge effect to encoder bitrates.
Using your AVC guesstimates for bitrate efficiency, I come up with 6 Mbps
for the AVC HD and 2.5 Mbps for the MPEG 2 SD, giving the simulcast a total
bit requirement of 8.5, whereas current ATSC single HD requires 12 Mbps.
Your mileage may vary. Keep in mind that the SD bitrate could be reduced
even further, which would introduce nasty artifacts but also give people
incentive to purchase the HD equipment. And none of this discussion
includes stat muxing, which is a big boon to reduced bitrate multicasting.
Simulcasting an SD and an HD version of the same program may negate some of
that savings, however, since both channels would be asking for more bits at
the same time. A slight delay on one channel might cure this, I don't know.
Bottom line is that even though it goes against the grain of an engineer's
"elegant solution" to have to simulcast an SD and HD version of a program,
in reality with more efficient codecs such as AVC, backwards compatibility
can be maintained with current hardware and new HD programming can be
delivered in the same or less space, and certainly no more space, than the
US approach.
Good things come to those who wait, I suppose.
John
----- Original Message -----
From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
> Here's a SWAG for you.
>
> For normal 24 fps shows, in ATSC you need avg 10 Mb/s.
> A simulcast would mean ~5 Mb/s SD + 5 Mb/s HD AVC. Of
> course, this can be tweaked down, both in MPEG-2 and in
> AVC.
>
> For 60 fps HD, you need some 16-18 Mb/s in ATSC. A
> simulcast would require still 5 Mb/s in SD and maybe
> 9-12 Mb/s in AVC. So not a big difference.
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