[mythtv-users] Various questions

Brian Steele steele.brian at gmail.com
Mon Sep 26 17:05:46 UTC 2005

On 9/26/05, kteague at speakeasy.net <kteague at speakeasy.net> wrote:
> Another gentleman by the name of Brian Steele responded to my post, also.
> He noted:
> <snip>
> You are correct, they are hardware tuners and they don't perform any
> hardware encoding. The reason they don't need to do this is that ATSC video
> is already encoded and compressed into MPEG2 before it is broadcast. The
> video recorded by the HD-3000 and Air2PC cards is just streamed over the bus
> directly to the hard disk with very little CPU involvement. I have two
> HD-3000 cards and can record with both at the same time while using less
> than 5% of a 3Ghz Pentium4 CPU. Playback on the other hand, requires quite a
> bit of CPU time. I average about 85-90% CPU usage when playing back 1080i
> <snip>
> That said, why would anyone need a hardware encoder if the stream is
> passed through the PCI bus and dumped directly to the hard disk as an MPEG2
> formatted file? And where does ATSC come in to play? I thought the signals
> we receive in the US are NTSC. Please forgive my ignorance.

Analog signals in the US are broadcast in NTSC format. Digital signals (SDTV
and HDTV) are broadcast in ATSC format. In my area, the major broadcast
networks are broadcasting in both formats simultaneously using two different
channels. ATSC is already MPEG2 compressed. NTSC is not compressed. You
would use a hardware encoder if you are recording analog signals either from
cable or over the air. Basically, digital broadcasts are just written to
disk because they are already encoded, analog broadcasts have to be encoded
before they are written to disk, either using a hardware encoder or doing it
in software.

Hope that helps.
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