On Mon, 13 Dec 2004, Dik Takken wrote:
> What I see when running 'top' is that the user CPU usage is about 90% and
> system usage 10%. This happens when I capture at 640x480 or higher
> resolution. I only get 100% perfect captures at 512x384 and below.
Hmmm, that is puzzling - I thought the card was supposed to be
doing the jpeg compression, almost sounds like some of that is
being done in the host.
> I would think that, since 12GB/hr is not exceptionally large, DV is still
> a bit of a space/quality compromise compared to MJPEG. This video format
25Mb/s - and no it's not a compromise compared to MJPEG. A lot of
progress was made in compression techniques between the era when
MJPEG was created and when DV (and it's variants) were invented.
There are also 50 and 100Mb/s variants but at that point you've
definitely left the "consumer" arena and are squarely in the
professional (and very expensive) realm.
> is not designed with video editing in mind, rather storage. MJPEG on the
> other hand is designed for video editing, not for storage. It's way too
That is incorrect. DV is an amazingly editable format - you should
see what an editing package like Final Cut Pro (from Apple,
but Adobe has a similar program for windows folks) can do with DV!
And there's no resampling of the square pixels to video pixels. If
you're NOT going to DVD or similar format then this isn't important
(if you only play the MPEG2 results on a computer). But if you do
want to go to DVD then the 1:1 pixels from the MJPEG card need to
be scaled/resampled to the 10:11 or 59:54 format used by NTSC/PAL.
> big for that. But maybe I'm wrong and the newer DV compression technology
> also beats MJPEG quality wise.
Try it - you'll like it :)
So far the only gainsayers are those who have never used DV <grin>
> > 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
>
> Wow. This sounds *very* interesting. I was already trying to find out how
Using 'dd' is not normally used but it is useful to be able to
quickly just get the middle 1000 frames out for testing using nothing
more than simple arithmetic and random I/O based on the record size.
Ordinarily you use "kino" or other editing program (smilutils) to
slice&dice the data.
> to generate SMIL files from a script in order to use the SMIL utils to do
> simple cut/paste operations. I want to be able to do as much as possible
> without needing GUI apps like Kino.
That's trivially easy to do.
> Could you please direct me to some more information about the DV format
> that can be useful when writing DV editing scripts?
Hmmm, usually I just use Kino or Final Cut Pro and either get a SMIL
file or another raw DV file that is used. Other than momentarily
extracting a clip or two for testing (or mailing to someone) I don't
do editing with scripts.
> > Can the PVR250, etc handle external devices such as a VCR? If so
>
> I want to edit the video after capture, so an MPEG2 capture card is not an
> option. The image quality is too low.
Ah, ok - so you want an editable format (that doesn't involve
decompressing MPEG2 and recoding it). Since MJPEG cards are
becoming hard to find (other than eBay) I'd suggest a DV solution.
Good Luck!
Cheers,
Steven Schultz
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