Re: video capture


<phil-news-nospam@xxxxxxxx> wrote in message
news:d9uk8v0225a@xxxxxxxxxxxxxxxxxxxx
> On Wed, 29 Jun 2005 11:02:28 -0400 David McCall
> <david.mccallUNDERLINE@xxxxxxxxxxx> wrote:
>
> | <demysaid@xxxxxxxxx> wrote in message
> | news:1120055738.256195.275800@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> |>
> |> Exactly. I'm not going to be using a TV Card because of the compressed
> |> 'quality'. This is why I want to capture it directly from a Television.
> |> Here's the question: Can I use any digital camcorder to do this or do
> |> I need a Prosummer digital cam/deck to do this?
> |>
> | Digitizing by shooting it with a camcorder isn't going to look very
> good.
> | If your TV has a video out, you could feed that video into a DV
> camcorder,
> | and then capture the DV stream via firewire. DV is still highly
> compressed
> | at 5:1 (25mbps), which works out to 11 gigabytes an hour. I don't know
> | that this would look any better than using a quality "TV card" though.If
> you
> | want uncompressed it would be about 5 times that.
>
> What would you recommend for capturing video (and audio) in uncompressed
> form when the source is baseband composite NTSC and two audio channels?
> Is there any separate device that can be connected to a PC with something
> like Firewire, or would it have to be a plug in card with all kinds of
> driver issues?
>
What Richard said. DVDs are substantially more compressed than
DV or HDV, but DV is a different style of compression than what is
used for DVDs. DV is kind-of like a string of JPEG pictures all
strung together in a single file. The important part to understand is
that each frame is a complete image. It is done that way to make it
more practical to edit. DVDs use a different style of compression
where you get one complete image and the frames that follow only
contain the parts of the image that are actually different from the
previous frame. When you have a locked off shot with a person talking,
the main thing that changes is the lips (of course the head moves
around a little, and he may wave his hands around or shift his body
position, but most of the frame stays pretty constant). I doesn't take
that much to keep up, so the picture quality can be pretty good.
When the shot changes to a new perspective, you normally get
another full frame, and then go back to just storing the difference.

This is not so nice for editing because you might want to make your
edit on one of those partial frames which means that the editing
software has to back track to the previous full frame and then
reconstruct the whole thing up to the point where you want your
edit to start. It also makes shuttling very difficult. DV doesn't have
this problem because each frame can stand on it's own.

Where this type of compression gets to be a problem is if there
is a lot of motion. In that case almost every frame is dramatically
different than the previous frame so the compression gets a lot
heavier in these areas. So, MPEG-2 compression is much more
efficient than DV. In fact MPEG-2 at the same data rate as DV
would look far better than DV could because of the improved
efficiency, but it would be much more difficult to edit than DV.
So, DVDs don't look as much worse than DV as you might expect,
given the numbers.

HDV is actually MPEG-2 similar to what is used for DVDs, but at
a much higher datarate than what is used to make DVDs. The quality
is surprisingly good until you get a lot of motion in the shot, then it
starts artifacting pretty badly. You don't notice it as much while the
tape is playing, but it is really obvious if you pause on an individual
frame. Because it is the same style of compression as DVDs use,
it is also difficult to edit. You either need to have software that can
keep a substantial buffer of complete frames, or you need to
convert the HDV footage to a different format that can present
each frame as a complete image.

OK, Capturing baseband video uncompressed requires special
hardware like the Full Digisuite, the Targa 2000, or other board
designed to do this. They used to cost several thousand dollars,
but I haven't priced them lately. You also need pretty fast hard drive
and computer to keep up with that much data (usually a RAID system.
It really isn't necessary for what you want to do.

If you are just capturing TV to store on DVDs for later viewing, there is
actually a good argument for capturing directly to MPEG-2 to eliminate
an extra step of compression. Every time you recompress a signal, it
goes downhill. This is particularly bad if you start with something that
is heavily compressed to begin with.

All satellite and digital cable is already heavily compressed, and if
you use a Tivo, is even further compressed. I'd bet that even most
over the air broadcast is pretty heavily compressed (especially HDTV).
You certainly don't need "uncompressed" for capturing this stuff.

Canopus makes several little boxes that you can feed video into and
get DV out that can be captured to the computer. I think the 110 is only
about $300, but the have other version that get fancier with TBCs and
noise reduction, but they cost more. This is a reasonable compromise,
because most computers can take in DV without any special effort.
Many DV and Digital-8 camcorders can take in S-video or composite
and put out DV as well, but not all of them do. The Canopus boxes may
do a little better job than a camcorder does (especially the more
expensive ones. Of course there are other companies that make
these devices. Canopus is just makes some of the most popular units.

You still might find that a good TV card will actually do what you want to
do just as well.

David



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