[mythtv-users] HDTV on Xbox frontend

Michael T. Dean mtdean at thirdcontact.com
Fri Sep 16 20:21:59 UTC 2005


A JM wrote:

> So, it's a processor intensive operation and requires some type of 
> video out allowing for the connection between FE and TV in a HD 
> format? Can this be done on a diskless system?

Yes.  Just need a good CPU (and perhaps video card) to do the work of 
decoding.

> If the BE does the recording (HD-3000) and the front end does the 
> displaying is that stream compressed as it travels the network?

Yes.  It /has/ to be compressed.  Here's why:

Given that:
1 GiB = 1024MiB = 1048576 KiB = 1073741824 bytes
(see http://physics.nist.gov/cuu/Units/binary.html )
1Mb = 1000 Kb = 1000000 bits

Standard definition recordings in MPEG-2 format require about 1.25GiB/hr 
(3Mb/sec) including audio up to a max of 4.25GiB/hr (10.08Mb/sec) at the 
maximum allowed bitrate for DVD's.  MPEG-4 recordings can, in theory, 
give the same quality as MPEG-2 with half the bitrate.

Uncompressed standard definition video will take much more space.  
Assuming 720x480 pixels interlaced recording using a 16-bit/pixel 
uncompressed format (like YUV or YUV2), a one-hour recording wuold take 
70GiB/hr (166Mb/sec) and a 24-bit/pix format (like RGB24) would take 
about 105GiB/hr (~250Mb/sec) not including audio.

So, even standard definition TV, when uncompressed, would require more 
network bandwidth than most people have--it would even be pushing the 
limits of gigabit ethernet.

1080i60 video has exactly 6 times the pixels (=6 times the data 
requirements) of 720x480i60, meaning that 1080i60 would require 
420GiB/hr (996Mb/sec) at 16-bits/pixel or about 630GiB/hr (1500Mb/sec).  
720p60 has almost 5.2 times the pixels of 720x480i60, so it requires 
basically the same bandwidth as 1080i60.

When compressed with MPEG-2, these 1080i60/720p60 recordings will take 
between 4GiB/hr and 10GiB/hr.  Assuming an average of about 7GiB/hr, 
that's about 16.8Mb/sec, or a max of 10GiB, that's about 24Mb/sec.

> I guess what I'm asking is can a wireless connection handle HD or does 
> it have to be wired?

You'll have to make the call based on your network performance and the 
above numbers, but you're likely to get much better results with a wired 
connection--especially when using high definition.

Mike


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