On Thu, Feb 26, 2004 at 09:31:07AM -0800, Ben Barrett wrote:
> For some reason, I thought that s-video carried audio as well. I've no
> experience there, so "no blood no foul"...
That wouldn't make much sense given the evolving standards for both.
Aside from the PAL vs. NTSC vs. SECAM issue, video currently comes in
these major flavors:
- Composite (single RCA plug, usually yellow)
- S-Video (mini-DIN connector, seperate chroma and luma)
- Component video
- YCrCb as 3 RCA plugs
- RGB (sync on green)
- 3 RCA plugs (some pro gear uses BNC)
- VGA connector
- RGBHV (seperate sync)
- 5 RCA plugs (some pro gear uses BNC)
- VGA connector
These are from worst to best, acutally. The most flexible is the five
signal RGB cable since it it gives equal colorspace to the three primary
light colors and offers seperate sync for various resolutions and timings.
This is basically VGA/SVGA.
Older fixed frequency gear (and anything designed to work with today's
televisions is fixed frequency) can get by just fine without any vsync
signal and depending only on the hsync which is multiplexed into the green
wire. Adapters to use old Sun monitors with normal video cards do this
multiplexing, and adapters to use multisync monitors on old Suns extract
the hsync and use some intelligence to create a vsync. I digress..
YCrCb is interesting because it applies the technique used by broadcast
television. When color TVs came out, B&W had been established and they
wanted compatibility. So, they left the B&W signal alone and added the
colorburst signal B&W TVs didn't even see. Basically, color TVs treat the
B&W signal as brightness and then use a signal for the difference between
the brightness and the red, and another the brightness and the blue.
What's left once you subtract these out is green. This leaves you with
high green resolution but pretty low red/blue. The Y (Luma) signal
contains the brightness and sync, the other two contain the color
differences.
S-Video is what happens when you combine the two color information lines
together into one signal and put the result in a single connector. It's
not quite as good as component video, but it's still pretty good. Most
say it's good enough. Four pins are used--two signal and two ground. No
idea why they adopted a single connector for both, but anyone who
remembers the old Commadore 64 color monitor has seen S-Video done as two
seperately shielded RCA plugs. Someone just decided to make one connector
out of it along the way.
Composite is the two S-Video signals mixed, giving you one signal. Short
of RF modulation, it's the worst thing you can do to the signal.
If you haven't guessed yet, Composite happened when someone decided to not
bother to modulate and demodulate the TV signal. S-Video happened when
someone decided not to mix Luma and Chroma. YCrCb composite happened when
someone else decided to output the signal without mixing the Chroma
channels together. RGB simply was what all of these things were before we
tried to make them sane for both B&W and color.
THANKFULLY, Audio is more sane. Sortof.
- Analog
- Signal level
- Line level (what you're used to)
- Mic level (weaker, you won't use it, usually needs preamp)
- Connector madness
- XLR (you won't use this)
- RCA (1-6 depending on channels)
- Headphone type
- Size
- 1/4 inch (dying except for mono for musical instruments)
- 35 mm (probably only stereo anymore for computers/headphones)
- Bizarre sizes and 3+ channels for camcorders and other weirdness
- Channels
- Mono
- Stereo (seperate or combined connector)
- Rat's nest of (almost always) RCA plugs for 3, 4, 4.1, 5.1, etc
- Digital
- Signal conduit
- Coaxial copper (RCA plug)
- plastic fibre (TOSlink)
- Signal type
- Stereo PCM
- AC3 (basically multi-channel MPEG audio)
Currently, non-embarassing AV gear accepts S-Video and stereo RCA.
S-Video plus TOSlink patch cables are becoming more common, but I think
those won't last because DVD players are making people start to demand
component video over S-Video more and more often. TOSlink will win over
coax because it's cooler (not because it matters since the signal is
already digital) and YCrCb vs. RGB is still up in the air. Both have a
strong push behind them. Although DVDs happen to be encoded in the YCrCb
format, the playback devices quite often render them to an RGB framebuffer
before re-encoding them for display. This is amusingly wasteful, but
lossless. ;)
> So, what are some reasonably good ways to determine how many milliseconds
> out of sync one's audio and video are?
When you figure this out, talk to the people making DVDs. Note that the
beginning of Fellowship of the Ring was out of sync in the theatrical DVD.
Most weren't terribly annoyed and those who don't work with digital AV
didn't even notice. ;)
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