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Old June 14th, 2004, 03:46 AM   #1
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Location: Belgrade, Serbia
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Firewire capture - variable data rate?

Hi,

my setup for capture/editing is PC with firewire card and Canopus ADVC-100 converter. Well I know that all dv codecs have constant 25Mb/s data rate. The question is, when capturing low quality vhs video via Canopus, is it possible to somehow use variable data rate because I dont need full 25Mb/s.
Maybe there is a software for real time encoding (mpeg2...) during capture.
Any thoughts?

Thank you
Best regards

Darko
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Old June 14th, 2004, 03:57 AM   #2
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Location: Holland
Posts: 12,514
Well no and yes. Let me explain:

1) the datarate coming from the ADVC-100 is 25 mbps (or mBIT/s).
NOT 25 MB/s. There is nothing you can do to change that. This
yields a 3.6 MB/s real-world capture rate.

2) In theory with enough hourse power you can convert such a
signal in real-time to either MPEG1 or MPEG2.

Regarding my point 2 above: I had a Dazzle on loan from a friend
and tried to find software that could do this. I think I found one or
two packages in the end (no, I don't remember which) that would
accept DV as input (realtime). Why? Because almost all of these
applications are geared towards TV cards or analog MJPEG boards
(which are basically the same except for a TV tuner).

So a lot of these products won't even work with a DV input. But
I found two or three in the end. Try search on keywords like:
VCR DV etc.

BUT, I found that neither of those programs actually worked. They
would see a DV stream for a couple of seconds and then quit. I
did get a few seconds in MPEG2 though.

But this might have been due to the Dazzle since I sometimes
had some other problems with it through regular capturing as well.

All I can say is find the software and try out the demo's.

Keep in mind that this works best if you DO NOT want to do
anything with the footage after capture. So it is simply to watch
a TV show for example or archive something. If you need to edit
the footage I would just capture in DV if you can and then encode
to MPEG after the edit is done.
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Old June 14th, 2004, 05:41 AM   #3
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Thank you Rob,

I know the datarate coming from canopus is 25 Mbits/s, I'll try to find some software for real time mpeg2 encoding.
The main purpose is to capture long vhs videos (3 or more hours), you know not for editing, just for converting analog video to mpeg1 or divx format. I could simply capture in dv, and then recompress, but I want to save disk space.

Best regards
Darko
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