On Mon, 13 Dec 2004, Richard Ellis wrote:
> On Mon, Dec 13, 2004 at 11:06:46AM +0100, Dik Takken wrote:
> >
> > So, I'm looking for a decent hardware MJPEG capture card that is
> > currently available in computer stores.
> I'm not so sure that such exists today. Unless you consider Ebay to
I think LML (Linux Media Labs) still makes them but they are the only
place I know of - and the cards are quite expensive.
> Keep in mind as well that for MJPEG, if you crank the quality of the
> recording up quite high, you'll also need a speedy hard drive to...
Yep - and I think that (more than the speed of the cpu) is what
is causing problems for Dik.
> if 320x480 frame then size_per_hour = 20.0 GB/hr * quality_factor/100
>
> if 640x480 frame then size_per_hour = 40.0 GB/hr * quality_factor/100
DV is a flat ~12GB/hr. Now some have mentioned that as a shortcoming
("you don't get to select the quality") - but it's a feature to me.
You can always degrade the image later :-)
> ... "quality_factor" is the -q option to lavrec. There's no entry for
> 704x480 or 720x480 simply because a DC10+ can't capture at more than 640x480.
That's because the DC10+ is capturing square pixels. Video pixels
are (for the US) 10:11. I'll leave the arithmetic as an exercise
for the reader but 640x480 1:1 pixels is the same as 704x480 10:11
pixels. But since you can't place a 640x480 frame size on a DVD
you have to resample from 640x480 to 704x480.
> > (external) capture devices that can convert analog video directly
> > to DV and stream it directly to your harddisk. How good/bad is the
> > quality of these devices?
>
> You'll have to discuss that with our resident DV advocate, Steven
> Schultz. The quality is quite excellent from what is reported.
Did someone mention my name? :)
The quality is excellent. And since you get the Rec.601 sample
size there's no resampling/scaling to do. You probably will want to
crop (not scale!) from the DV 720xN frame size to 704xN because the
analog->DV converters place the full video frame (704xN) inside a DV
720xN frame. Cropping doesn't use much cpu time at all and there's
no 'conversion/resampling' being done.
> I think Steven would say that DV would offer better quality than the
> MJPEG solution. DV is also a newer compression algorithm and as such
> it had the opportunity to learn from MJPEG and correct some edge
> conditions that reduce MJPEG's potential quality.
Indeed. And the cost, today, is less. A Canopus ADVC100 and a cheap
IEEE1394 card is less $$ than a MJPEG card and the raid-0 array needed
to handle the I/O requirements. No need for a raid array since
any disc these days (even external IEEE1394 drives on the same bus
as the capture unit) can handle ~3.6MB/s.
Another "feature" (which I've used fairly often) of DV is the fixed
record size - for "NTSC" the DV records are 120000 bytes and "PAL
144000 bytes. You can use "dd" as a simple/crude editor (and with
'locked audio' - one of the benefits of the Canopus product line) you
don't have to worry about slicing thru an audio sample.
> might also consider one of the hardware mpeg2 compression boards
> instead of a MJPEG/DV solution. I can attest that the Hauppage WinTV
> PVR250 card's will generate a simply beautiful picture from analog
> cable TV, and there's no fuss/muss with needing to re-encode anything.
Can the PVR250, etc handle external devices such as a VCR? If so
that would be a good approache, but if the goal is to convert
old tapes to DVD then something like the Canopus unit would be a
very good choice.
Cheers,
Steven Schultz
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