[mythtv-users] Hardware Question

[Andrew Dodd]

Quoting Bill Chmura <Bill at Explosivo.com>:

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> On Tuesday 02 March 2004 12:40 am, Len Reed wrote:
> > Dex West wrote:
> > > So I've read about people purchasing a 250 & 350.  I'm
> > > assuming the 250 is used for recording and 350 is used
> > > for playback??  That seems like a lot of money to
> > > spend if I have to buy both.
> >
> > No, the 350 seems to be a superset of the 250: it has hardware MPEG2
> > decoding as well as encoding.  The 250 has only encoding.
> >
> > Now, for what I'd like to know in a similar vein.  I currently have a
> > mythtv setup with a WINTV board (software encoding) on a single backend
> > machine and Nvidia TV-out cards on two different frontend machines.  I'm
> > considering buying a PVR250 or 350.
> >
> > 1. With the 350 and mythtv can I record one program and view another
> > simultaneously using just that card?  Surely the answer is yes.
> 
> You can record one program and view another program that you already
> recorded.  
> You cannot record on program and watch live TV through mythtv.
> 
> If you have another tuner card you can do both
I'm pretty sure that the 350 CAN do liveTV, but I believe that it's
significantly more likely you'll have one of the infamouse ivtv hangs.  Again,
it's a situation that some people experience on a regular basis (and hence ditch
the 350's TV-out to avoid) while others have no problems whatsoever.  (As I
mentioned before, I believe Isaac himself is one of these lucky ones.)

> > 2. If I have a both the PVR350 and the existing low-end board on my
> > network can I watch things on the 350 that I recorded (in RTJPEG or
> > whatever) on the other board?  It seems that I can't, and that I'll have
> > to use software decoding to an AGP TV-out card.  If so, perhaps the
> > cheaper 250 makes more sense?
> 
> I could be wrong, but right now the issue is with the IVTV framebuffer in the
> 
> driver.   I think once that issue is resolved it will be okay...  But I have
> 
> no idea when / if that will be.  You can check the Ivtv stuff for that. 
It is an issue that will never be resolved.  It's a hardware limitation - With
the exception of the dedicated MPEG-2 hardware decoder, the 350's TV-out is a
completely non-accelerated raw framebuffer.  It can theoretically display
anything, the problem is that it can't do scaling or colorspace conversion, thus
all of that must be done in software, which REALLY slows things down.

I once was involved in a videoconferencing project.  At the time we were running
P3-500 machines.  When converting 320x240 video from YUV-RGB and then
pixel-doubling it in software our CPU usage would be 90%.  Once X started
supporting hardware scaling, we implemented that for output and our CPU usage
for simultaneous encoding/decoding dropped to 10-20%.

> >
> > 3. If I use mythtv's transcoding (say, to remove commercials) on an
> > MPEG2 file that was made by a 250 or 350, must the resulting output then
> > be non-MPEG2?
> 
> As I understand it.  You then lose the hardware decoding.  The suggestions I
> 
> have found was to use avidemux2 to do commercial removal.  Started playing 
> with that tonight, and while it was a snap removing the commericals I am 
> encountering some strangeness also...
Are you using avidemux2's native DVD Program Stream export capability?  That's
still under development.  I save seperate raw audio/video streams and remux them
using mplex from mjpegtools.

Note that these can't be replayed reliably in Myth due to the fact that the
recordedmarkup DB table of GOP beginnings must be regenerated for the new video.
 Unfortunately, there is currently no way to regenerate the GOP tables for an
arbitrary recorded video, it is only done during the initial recording.  They do
burn to DVD (via dvdauthor) quite easily though.  :)