[mythtv-users] mythtv hardware plans

Brian Wood beww at beww.org
Sat Feb 3 22:41:20 UTC 2007

On Feb 3, 2007, at 3:26 PM, Rod Smith wrote:

> 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.

Perfectly well put. Myth has no way to get MPEG-2 recordings directly  
from a frame grabber, though you could certainly record as MPEG-4 and  
the transcode to MPEG-2 if you wanted to make a DVD. RTJpeg requires  
less CPU than MPEG-4 but creates larger files. In any case using a  
framegrabber capture card would possibly require a faster CPU if you  
wanted to record SD and playback HD at the same time.
>> 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.

Right again. It was a difficult thing to do the last time I tried it,  
you had to unload modules and reload different ones. I knew it was  
being worked on so I'm glad to hear it's working well now, at least  
for you. Sounds like the screwing around with the DVB drivers has  
finally settled down with 2.6.19.

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