[mythtv-users] TV out for unlisted card?

[Rod Smith]

On Sunday 01 April 2007 21:45, Angus wrote:
> Nick Morrott wrote:
> > You *may* be able to get away with a PCI/AGP-based NVIDIA MX440 type
> > (or later MX4000) card that has TV-Out. I'm not current on the level
> > of TV-out support in the open source NVIDIA driver, so you may need to
> > ensure you get a video card supported by the NVIDIA binary driver.
>
>     Before I go for a card, I need to be certain it will work. This is
> the sort of thing I want to get right the first time, unlike the capture
> card I bought which I thought was also TV out.

You're unlikely to find a 100% guarantee that ANYTHING will work -- even if a 
card works fine on System X, it may not work at all on System Y because of 
idiosyncratic incompatibilities with other hardware or with specific software 
configurations (kernel versions, 32- vs. 64-bit, etc.).

That said, I can say with certainty that I've used two cards based on nVidia 
MX4000 chipsets in a MythTV box. Both worked fine for SD, although one 
produced blue screens when playing back HD content at SD resolutions. Whether 
they'd be fast enough on your 800MHz system, though, I cannot say, as my 
system has a 3.06GHz Celeron-D CPU.

>     How would I know if my card is "non-hardware"? And of all the cards
> I looked at, I don't remember seeing XvMC as part of their advertised
> specs. Is it not a popular standard?

XvMC is the name of the software library for Linux that uses certain hardware 
acceleration features when playing back MPEG-2 video. Here's the MythTV wiki 
entry on it:

http://www.mythtv.org/wiki/index.php/XvMC

Because XvMC is a Linux (or perhaps Unix more broadly; I'm not sure of that) 
standard, hardware manufacturers ignore it in their marketing.

XvMC is largely independent of the hardware encoding feature of some capture 
cards, since XvMC is a playback standard. The two interact, though, because 
most capture cards that do hardware encoding produce MPEG-2 video, which is 
what XvMC helps with. Software encoding capture cards (aka framegrabbers), 
though, produce a video stream that's normally compressed by the software, 
and MythTV only supports RTJpeg and MPEG-4 as its formats for framegrabbers. 
Thus, if you use a framegrabber capture card, XvMC support won't do you much 
good, at least not for your TV playback. (You might get files in MPEG-2 
format from other sources, though. DVDs, for instance, are in MPEG-2 format. 
You could also transcode your MythTV recordings to MPEG-2 format, although 
not with tools built into MythTV, unless you count using MythArchive to make 
DVDs.)

>     Well, looking at my capture card (KWorld Global Terminator) it says
> it supports MPEG-4/2/1 but then also says (note: codec need(sic) to be
> downloaded from internet). What does that mean?

I suggest you read the following wiki entry:

http://www.mythtv.org/wiki/index.php/Video_capture_card

Your card is clearly listed there as a software encoder card. It'll consume 
most of your available 800MHz CPU to encode video. In fact, an 800MHz CPU may 
be inadequate for some resolutions, quality settings, etc.

Most hardware manufacturers don't make clear distinctions about the features 
that are important to Linux consumers. This is definitely the case on the 
matter of hardware vs. software encoding video capture cards. You really need 
to research the specific product you're buying rather carefully. Good 
references include the MythTV wiki and the v4l wiki, both of which tell you 
about the features that are important (although on a somewhat spotty basis -- 
they are wikis, after all).

-- 
Rod Smith
http://www.rodsbooks.com