[mythtv-users] mythtv hardware plans

Rod Smith mythtv at rodsbooks.com
Sat Feb 3 22:26:52 UTC 2007

On Saturday 03 February 2007 17:05, Brian Wood wrote:

[re: pcHDTV cards' HD and SD support]

> You should be aware that using those cards as analog tuners requires  
> a lot of CPU because they are just straight frame grabbers, all the  
> compression/encoding has to be done by your CPU. The PVR cards have  
> on-board MPEG-2 encoders and thus take almost no CPU. You might well  
> be disappointed with the analog performance of the HD 3K/5.5K cards.

This is true; however, any computer that's capable of playing back HD content 
will be able to handle recording NTSC via a frame grabber card like the 
pcHDTV card's SD/NTSC tuner, and probably two or three at a time, at that. Of 
course, there'll be a range of CPU speeds in which playing back an HD stream 
will consume so much CPU time that recording will then become impossible.

One thing that might be worth mentioning is that most cards with hardware 
encoders output an MPEG-2 stream, whereas MythTV supports either MPEG-4 or 
RTJpeg for its software-encoding cards. If you prefer one format or another 
(say, MPEG-4 for greater compression or MPEG-2 for quicker output to DVDs), 
that might be a factor that's worth considering.

> Plus it's a "one or the other" proposition, you can't switch on the
> fly easily. Think seriously about a PVR for analog signals.

I'm not sure what you mean by that. My pcHDTV 3000 cards can switch between HD 
(QAM-256) and SD (NTSC) inputs; I just input the appropriate channel number 
and it's recording. (I'm only recording NTSC via composite and S-video 
inputs, though.) It takes a couple seconds to switch modes and begin a new 
recording file, but your comment reads as if you've got to configure them to 
function ONLY as HD or ONLY as SD tuners, and that's certainly not true. I'm 
using the DVB driver in a kernel with a pcHDTV 3000, though; it's 
possible there were more severe limits in earlier drivers and/or with other 
pcHDTV models.

Rod Smith

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