[mythtv-users] recommendations for a media box

[Michael T. Dean]

Dr NoName wrote:

>Hi everybody,
>
>I am trying to spec out a pvr system. I want to be
>able to record tv, play back, do live pause, watch
>dvds, etc. and use the remote to  operate  it. The box
>will be connected to TV only, with no monitor
>attached;  hopefully no keyboard & mouse either.
>Ideally it should be a tivo on  steroids.
>
>Here are the specs I have to work with:
>
>AMD Athlon XP 2400+
>512MB RAM
>  
>
I highly recommend DDR SDRAM (PC2100 or above) for best results.  
Although PC100/133 will work, it may have some detrimental effects (such 
as increasing transcoding time, decreasing stability of IvyTV 
(PVR-350/250) drivers, etc.).

>40GB HD (plus possibly a second 120GB HD)
>DVD-ROM
>DVR+/-RW
>10/100 NIC
>on-board 5.1 sound card & speakers
>running Debian or Mandrake -- not sure yet
>
>TBD: video card, tv capture card.
>
>Here are my questions:
>
>1. What codec should I use? I want it to be fairly
>high quality and  compatible with everything, so I'm
>thinking either mpeg2 or divx. I am  willing to spend
>more CPU cycles to get better quality (after all, it 
>will be a dedicated media box). I have never heard of
>rtjpeg, so I don't think I'll use that.
>  
>
Depends on what card you're using.  If using a hardware encoder card, 
the decision is already made for you.  I.e. the PVR-x50 encodes to 
MPEG2, the Zoran-based cards encode to MJPEG, etc.  Afterwards, you can 
"transcode" from, for example, MPEG2 to MPEG4.  Note, also that DivX is 
a proprietary CODEC used to create an MPEG4 video; XviD (i.e. DivX 
backwards) is an open-source CODEC that does the same.  (You can play 
back either DivX or XviD MPEG4 files on Windows, too.)

Note that all of the supported formats use lossy compression, so none 
are "perfect."  This also means that if quality is your primary concern, 
you'll want to keep most recordings in the format in which they were 
recorded to avoid further loss of information.  It's also a lot easier 
than transcoding.

Also, with RTJPEG you could theoretically get "perfect" output using 
100% quality (i.e. 0% compression) (so I wouldn't dismiss something 
outright just because I haven't heard of it ;).  Myth probably doesn't 
allow 100% quality RTJPEG, but you wouldn't want it, anyway, because of 
the resulting file size.  Basically, you can think of RTJPEG as just a 
bunch of JPEG images--which I'm sure you've heard of--and a synchronized 
sound stream.  Also, RTJPEG--unlike MPEG--allows for "frame-accurate" 
editing of videos (because each frame stands on its own)--not that 
that's much of a concern for a PVR.

>2. What is the CPU utilization when encoding in that
>format? What about decoding?
>  
>
On my PVR-350 using the PVR-350's TV out, SETI at home gets about 99% of 
the CPU when encoding and decoding simultaneously. ;)  With a PVR-250 
(or a 350 using a VGA card's output), your CPU does the decoding, but 
encoding is handled by the card.

>3. Is it worth getting a hardware encoder
>(specifically Hauppauge PVR-250)? What's the CPU
>utilization then? If not, which card do you recommend?
>  
>
I highly recommend it-especially if there's any possibility you may ever 
want to add additional tuners to the system (i.e. 2+ PVR-250's).  The 
PVR-x50's also provide high-quality captures.

>4. There are two options for tv-out:
>
>  - TV capture card with TV out (such as Hauppauge
>PVR-350) with no video card (I'm assuming I don't need
>a video card then)
>OR
>  - plain TV capture card + video card with TV out
>(Nvidia GeForce MX  or  an old ATI Rage II).
>
>I am leaning towards the second option since this
>would allow me to  connect a monitor for debugging and
>what not. Which one would you recommend?
>  
>
I recommend staying away from the PVR-350's TV out, for now, because:
 - The TV out support is still very experimental, so system stability 
suffers (quite a lot).
 - The 350's TV out driver for X-Windows does not support Xv (the X 
Windows video extension), so any video not decoded by the 350 (i.e. 
MPlayer and xine for things like DVD, QT, DivX, WMP, etc.) is done using 
mmap'ed I/O to the card's frame buffer--which is significantly more CPU 
intensive than using Xv.  My Athlon XP 1700+ cannot play DVD's through 
the PVR-350's TV out.
 - There is absolutely no 2D or 3D hardware acceleration for games, so 
it's not very useful for MythGame (MAME, Tux Racer, etc.).
 - The 350's TV out is not initialized by the BIOS, so until you load 
the IvyTV drivers and start X, you will have no useful output on your 
screen.  Instead, you will see "garbage" output (strange white bars with 
a "ghost" view of the last screen displayed on the frame buffer), which 
makes the system look a little less than polished.

I have a PVR-350, but I'm planning to switch to using VGA out to a VGA 
to NTSC converter (see 
http://www.gossamer-threads.com/perl/mailarc/gforum.cgi?post=103525 
)--as soon as I build the converter.  A friend and I are building Myth 
systems, and this was the test system.  After testing the 350, my friend 
will be buying 250's for his system (since we won't be using the 350's 
TV out).

>5. Where does the sound go? The TV out outputs only
>video, so I'm  assuming I still need speakers when
>playing back a recording. But what about live tv? My
>tv has only RCA inputs and no outputs.
>  
>
 From source to PVR-x50's RCA inputs.  If using the PVR-350's decoder, 
sound comes out the PVR-350's RCA outputs.  If not using the decoder 
(i.e. on a PVR-250 or a PVR-350 playing MPlayer or xine videos), sound 
comes out the sound card's output.  Therefore, you usually hook a RCA 
L/R to 3.5mm stereo jack from the PVR-350's RCA outputs to the sound 
card's line in.  Then, the sound is output through the sound card.  BTW, 
When KMF said, "TVout carries audio, too," he meant that the same output 
used for TV-out on the card has audio out.  An adapter (bundle of 
cables) plugs into this output and splits the video and audio signals 
into standard connectors (i.e. S-Video, RCA Composite video, and RCA L/R 
audio)

Note, however, that the only output possible from the PVR-350's decoder 
is 2-channel analog output.  Therefore, if using the MPlayer plugin that 
sends, for example, DVD MPEG streams to the decoder, you lose the AC-3 
(5.1ch) stream.  Therefore, you will probably want to use MPlayer or 
xine without the decoder to get full audio capability from your 
5.1-capable sound card--which means, you will probably want an 
Xv-capable video driver...

Also, the PVR-x50's only support capture of stereo (2-channel) sound.  
Therefore, if your source uses surround sound, you will only get 
stereo.  I'm pretty sure this is the same with any other tuner card that 
you can get.

>6. How well does the remote work? It's quite important
>for a dedicated  media box.
>  
>
Wonderfully for things like Myth.  Not so well for bash. ;)  In other 
words, you will probably need a keyboard, but thanks to the wonders of a 
network operating system and OpenSSH, it doesn't have to be connected.  
Also, the quality of the remote will affect the reliability of the remote.

I'm using an ATI Remote Wonder (radio-frequency) remote to send signals 
to the Myth box and using a serial-port IR transmitter to allow the Myth 
box to send signals to my components (A/V receiver, TV, Dish Network 
receiver, VCR, etc.).  It's great being able to use one button on one 
remote to send multiple signals to multiple components.  Never seen a 
TiVo that could do that...

>any other suggestions are welcome.
>  
>
Patience is a virtue (that carries a lot of wait).  In other words, you 
will spend quite a bit of time learning Myth's quirks, getting your 
system set up correctly, tweaking your system, etc.  If you approach it 
as a learning experience, it's time well spent.  If you're planning to 
throw together a Myth system to save some money over buying a TiVo, you 
will probably decide that the TiVo is cheaper after factoring in your 
time.  However, once you've invested the time, the system you get from 
Myth is far better than any "off the shelf" system you can buy.

Mike

Note: The opinions expressed in this e-mail come with a full money-back 
guarantee.  If you later find that information gleaned from this e-mail 
lead you to make "the wrong decision," I will be happy to refund the 
full price you paid me for my opinions.  (In other words, this is just 
one point of view.  I am not responsible for any decisions you make 
based on my input...  :)