Re: [xine-user] computer far from TV set

[Lawrence <xin...@gl...>]

At 02:13 PM 7/10/2002 +0200, you wrote:
>Hi guys,
>a bit off topic but I need the answer for better use of xine. I noticed
>xine supports nvtv, I got TV out on my nv card (so far so good) but I
>have my computer located in another room than the TV is. I wonder what
>is the max length of SCART like cable (i.e. video and audio) that would
>be able to transfer the signal from xine/TVout to my TV in a reasonably
>(i.e. better than DVD) quality?

    SCART is unfamiliar to me; I'm on NTSC (Never Twice the Same Color) on 
this side of the pond. But looking it up on the 'net, I see that SCART 
connectors for PAL (aka. "FlickerVision") are actually pretty similar to 
baseband video here.

    Note that NTSC (the North American TV standard) was designed in the 
late 1940s, and that PAL (Euro TV standard) was designed in the mid 1950s. 
Your computer monitor is based on ~1985 IBM VGA standards and has been 
improved since. At the very most generous, your computer monitor reflects 
35 years of technology that your TV set doesn't have, and the difference in 
quality will be evident. Unless you've got HDTV, the new digital TV 
standard. It's the fact that we keep on carting around these old TV 
standards which lets me turn on my 1951 Westinghouse to watch the news, or 
hook my DVD player up to my 1955 Motorola to watch I Love Lucy re-runs. All 
non-HDTV sets are based on these ancient standards; TV hasn't changed much 
(technically) since then.

    Note also that DVD still frames are of a higher resolution than a TV 
picture. NTSC is 525 lines broken into 2 interlaced fields refreshed 60 
times per second; PAL is 625 lines in 2 interlaced fields at 50 times per 
second. The effective resolution of each is therefore about 275 and 300 
horizontal scanning lines (because interlaced lines are really supposed to 
ride on top of each other), and the vertical resolution (effective columns) 
is a function of the analog properties (frequency response primarily) of 
your equipment and cabling.

    Whassat all mean? Imagine an old VGA monitor at 640x480. About half 
that - 320x240 - is typical NTSC resolution. PAL will be about 340x240. 
Don't expect your DVD to look any better than a good TV picture; nowhere 
near as good as on the computer monitor.

>The distance here is like 7 metres straight but I wish I could hide the
>cable in the walls and ceiling which would then require no less than 15
>metres. What do you think? (asking for real experience before start
>buying the cables - maybe that it's possible to buy a higher quality
>cable if long distance is needed?)

    Okay. Assuming you can get the connectors you need for each side, and 
you know how to solder.

    - SCART appears to support either RGB or composite video, depending on 
how it's wired. Choose RGB for better quality if both the TV out on the 
video card and your VCR support it. (Go to the VCR; I'm sure you'll 
eventually want to videotape something you've downloaded.) RGB will require 
6 coax cables going from room to room, composite only 3.)

    - I suspect/assume SCART video is 75 ohm impedance. Get 75 ohm coaxial 
(screened) cable, enough for four passes (RGB) or one pass (composite). 
Find pinouts online. Red to red, green to green, blue to blue, sync to 
sync; or go composite out to composite in.

    - Audio - get screened (coaxial) microphone cable, as would be used on 
cheap (non-professional) mics. Professional mics use balanced line, not 
useful for your application. Left to left, right to right. Make sure all 
the shields (braids) on the coax cables are properly grounded.

    - Avoid cobbling something together with unshielded cable or lots of 
connections; go directly from source to destination. Building up 15m with 
three 5m cables is a very bad idea; each connector will result in an 
appreciable insertion loss. Using lamp cord, Cat-5, twisted pair, etc. will 
carry the signal and to some people might even look okay, but you'll induce 
hum in the audio and the impedance mismatch on the video will cause loss of 
resolution (smeary video because sharp changes in contrast will be made 
more gradual), ghosting, etc. Don't do it.

    - Be sure that the TV/VCR and the computer are connected to the same 
ground. If your house/apartment is old or the building codes are poorly 
enforced where you live, *make sure* that they're plugged into the same 
outlet, even if that means that you're running an extension cord along with 
your audio/video "snake". Lots of times, grounds are poorly cabled, 
resulting in voltage differences from ground to ground; usually the current 
flow is minimal (microamps) but enough to make a hum.

    If you're gonna do this, spend the time and do it properly. It's worth it.

>P.S. Note that I know about piece of hardware that is able to transfer
>video and audio wireless but all solutions I saw were stereo only and
>xine needs 5.1 so this is not an option for me (not to mention the
>price).

    Add more channels on your cable! You're gonna have quite the snake 
going from room to room, but short of moving the computer to the same room 
as the TV, there's no other way.

    Now, if anyone knows how to get Xine to repeat a given file 
indefinitely, and/or to save the playlist under a different name, please 
let me know.

    Lawrence Wade
    fmr. Professional Senior Video Technician, Toronto SkyDome.