Log in Register FAQ Memberlist Search pcHDTV Forum Index
pcHDTV Forum

pcHDTV Forum Index -> Installation/Setup -> PVR noob has some questions
Post new topic  This topic is locked: you cannot edit posts or make replies. View previous topic :: View next topic 
PVR noob has some questions
PostPosted: Fri Aug 18, 2006 3:23 pm Reply with quote
sciguy125
 
Joined: 18 Aug 2006
Posts: 4




I'm planning on making myself a PVR. I guess I'll start with my proposed setup.

Nvidia GeForce4 MX440
pcHDTV HD5500
Pentium M ~1.7GHz
512MB RAM

I want to use a Pentium M for it's low power consumption. Depending on the motherboard I end up with, the RAM will probably be DDR.

1.) any general comments on this configuration?

2.) I'm a little unclear about what hardware handles the encoding. I realize that the pcHDTV cards don't have a hardware encoder, so does that mean that the CPU has to handle everything while recording?

3.) Similar to my previous question, what happens if I watch something live while recording it? I know that the video card will decode for playback, but does this apply while also recording?

I may have more questions after I have some time to think a little more.
View user's profile Send private message
Re: PVR noob has some questions
PostPosted: Sat Aug 19, 2006 6:47 am Reply with quote
iwantmyhdtv
 
Joined: 05 Jan 2005
Posts: 12




sciguy125 wrote:
I'm planning on making myself a PVR. I guess I'll start with my proposed setup.

Nvidia GeForce4 MX440
pcHDTV HD5500
Pentium M ~1.7GHz
512MB RAM


If you want low power consumption, you should get an Intel Core processor (preferable dual core). They are faster than the Pentium M, and speed does matter when watching HDTV.

sciguy125 wrote:

2.) I'm a little unclear about what hardware handles the encoding. I realize that the pcHDTV cards don't have a hardware encoder, so does that mean that the CPU has to handle everything while recording?

Analog and digital are handled differently.

NTSC analog is digitized and send by the card to the CPU uncompressed. So if you want to record/store it compressed, the CPU does indeed have to perform the compression.

ATSC digital is compressed by the television station before it is even broadcast. The tuner card receives this compressed stream and just passes it along to the CPU. So no additional compression is needed for recording, you can just store the broadcast stream directly. On the other hand, you need software decompression to WATCH it, and this is where a powerful CPU is necessary, especially for 1920x1080i transmission. The nvidia card you are getting has XvMC which can help also.

sciguy125 wrote:

3.) Similar to my previous question, what happens if I watch something live while recording it? I know that the video card will decode for playback, but does this apply while also recording?


It's not a problem. Like I said above, "recording" just involves writing the broadcast to a file without any extra processing, so in terms of resource usage it is no different from just watching.
View user's profile Send private message
PostPosted: Sat Aug 19, 2006 9:09 am Reply with quote
sciguy125
 
Joined: 18 Aug 2006
Posts: 4




I'm still a little fuzzy on the decoding process. When an ATSC stream comes in, it's already decoded, so recording it is just a matter of writing it to the disk. In order to play it though, it needs to be decoded before being sent out to whereever it's going. A compatible video card will do this and not load down the CPU. However, with NTSC, the video needs to be encoded by the CPU. So, does this mean that it will be encoded then decoded while even watching it live? It seems to me that the processor requirements would be greater for NTSC than with ATSC. ...of course NTSC is much lower resolution so I'm not sure how that affects things... If I go with a Core Duo, what speed would you recomend?

I want to be able to record while also watching it live. Ideally, I want to get a powerful enough processor such that in the future I have the option of getting a second tuner that can record while I watch another channel. Part of the reason I want to build a PVR rather than buy one is to make it possible to upgrade rather than simply buy a whole new system.

I found a nice motherboard for Core Duo with gma950 video onboard. Has anyone had experience with gma950? I've read that it works with XvMC. I couldn't find any actual reports of using it for HDTV though.

By the way, I downloaded tst.tar from the download page, but I couldn't figure out what to do with it. tar claims that it doesn't recognize it. I tried playing it in both xine and mplayer, but nothing happens.

Addendum:
Further research leads me to believe that the Intel video drivers only support Xv, not XvMC. Will that still work?
View user's profile Send private message
PVR requirements
PostPosted: Thu Nov 02, 2006 2:08 pm Reply with quote
photonwave
 
Joined: 10 Nov 2004
Posts: 45
Location: Carlsbad, CA




Here's what I can tell you from my experience.

I've not configured my setup to use XvMC, so my processor is doing all the work when I'm watching live/recorded shows.

To view a 1080i stream, I needed no less than a 2.8 Ghz processor. Less than that and the image stuttered on fast moving scenes (as in watching ER when the camera swings around and everybody is running around).

Also, when I initially tried using a 128 MB video card, the card produced an image where the right third of the screen was colored a solid color (pink) (I assume that I ran out of video memory). The left side of the screen looked fine. If I used mplayer to scale the image down before playing, then more of the image could be displayed. So, I finally went out and purchased a 256 MB video card and the issue was solved.

I would also suggest 1 gigabyte of RAM. RAM is cheap.

As someone else pointed out, recording video does not use up much processing power, but if your processor is peaked out rendering a 1920x1080 interlaced video stream, whenever your processor is busy doing something else, you're liable to see some frame dropouts.

I worked around that problem by configuring one machine to record HDTV transmissions, and another (connected via gigabit ethernet cards) to view with.

Now, if you don't want to upgrade your processor, you can scale your video streams down to 960x544 (or smaller), and you may be able to view video with fewer dropouts.

As far as the tst.tar file you downloaded, you'll need to "untar" the file into the "*.ts" file:
Code:
tar -xvf tst.tar
will do the trick

For reference purposes, here is my setup:
- Gentoo Linux
- 1 gigabyte memory (viewing machine), 512mb on recording machine
- 256 MB video card (NVidia GeForce) on viewing machine
- I use dvbstream to record shows
- I use mplayer to view shows

_________________
Gentoo 2.6.23-r3, pcHDTV 2000 and HD-5500, CM 4221 Antenna, MythTV
View user's profile Send private message
PVR noob has some questions
  pcHDTV Forum Index -> Installation/Setup
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
All times are GMT - 7 Hours  
Page 1 of 1  

  
  
 Post new topic  This topic is locked: you cannot edit posts or make replies.  


Powered by phpBB © 2001-2003 phpBB Group
Theme created by Vjacheslav Trushkin