> DA> You can always digitize the
> DA> video, scan rate convert it, and show it on a display at another
> DA> resolution/frequency (which is what the AV Macs would do in this
> DA> situation).
> Hmmm... Wouldn't it be slightly difficult to grab video when you can't
> view what you grab until *after* you've grabbed it?
sent to a separate pixel data port on the RAM/DAC where it is mixed with
the computer generated graphics. Thus, the video being grabbed is visible
on the display at all times.
No, Apple doesn't sell any multisync displays. However, you don't need aQuote:> DA> Full screen
> DA> video can be shown at the full frame rate of the incoming video -
> DA> 60/50
> DA> fields/sec for NTSC/PAL video. Note that with only 1 MB of video RAM,
> But not on a SVGA monitor, right? You'd need a multisync, right?
> (BTW - does Apple sell any multisyncs?)
multisync monitor for this, as the digitized video can be seen on any
display supported by the machine (from NTSC on up to 1152x870 75 Hz
noninterlaced). There are some tradeoffs on the size and pixel depth of
the video window and the display size/pixel depth and amount of available
I think so, but I could be remembering incorrectly. If you do the math,Quote:> DA> (I believe I've heard numbers on the order of 15 fps or so for a
> DA> 320x240 window.) You really need hardware compression to make this
> 15fps for 320*240? But that's sustained, not just a short burst to RAM?
that's a bit over a 2 MB/sec. data transfer rate. You would need a fairly
fast hard disk to support a this on a sustained basis, but they do exist
and are available on the AV machines. There's probably some sort of
software compresssion being used to reduce the data rate (although that is
just speculation by me as I don't have a Q840av readily available for
Good question. To the best of my knowledge there aren't any currentlyQuote:> DA> feasible. The AV Macs allow the easy addition of hardware compression
> DA> by providing a slot for access to the digital video pixel data stream.
> What kind of compression is available for the AVs? MPEG?
available hardware compression cards which use this slot. I have seen
MPEG demonstrated (so I know it's certainly possible to produce an MPEG
hardware compression card), but I don't believe anyone actually sells this
yet. Certainly all of the QuickTime software codecs are available, but
that's a far cry from what's possible with hardware compression.
- Dale Adams