sequence grabber vs video digitizer

[inge at mandli.com]

Steve,

Thank you for the reply. I have a few questions, though.

>>Is it possible to just use Sequence Grabber function calls?
>
> Yes. Look at the SGDataProc sample code in the Apple QuickTime
> examples for how to do the same thing using the Sequence Grabber.

As far as I understand, Sequence Grabber only grabs a frame every x ms.
Let's say if the frame rate is 15 fps, then it will capture a frame every
1/4 sec. If I want to capture a frame within that 1/4 sec interval, it
will return the frame captured last time, not at that time instant. Is
that correct that Sequence Grabber only grabs frames periodically, in
free-run mode?

In my project, I need to capture a frame close to real-time, at that time
instant. The camera will be mounted in a vehicle moving at 65 mph or more.
The max frame rate of the camera is 14 fps, so the difference of 1/4 s in
65 mph is about 15-20 feet, which is not tolerable.

Do I have to use Video Digitizer than?

>>Which Video Digitizer function calls should I use to interface with
>>the IOExperts API?
>
> I need to come up with a complete list of calls, but you need to
> initialize the digitizer:
>
> VDGetDigitizerInfo()
> VDSetInput()
> VDSetInputStandard()
> //some other stuff
>
> VDSetCompressionOnOff(true)
> VDGetCompressTypes() -- returns a set of supported formats
> VDSetFrameRate()
> VDSetCompression()
> VDGetImageDescription() -- tells you what you're getting
>
> now, to grab a frame
> VDCompressOneFrameAsync()
> VDCompressDone() -- loop until you get a buffer
> // use the buffer -- probably DecompressImage() or
> DecompressSequenceFrame()
> VDReleaseCompressBuffer()
>
> when you're done
> VDSetCompressionOnOff(false)
>
> One thing you can do is install the logging version of the IOXperts
> driver (look in the same directory as the release driver on our ftp
> server) and watch the calls made by the sequence grabber in the
> console. (We log under /Library/Logs/IOXperts/

Do I still have to call those functions even if I just want to capture raw
images (not compressed)?

Thanks much,
Inge Yuwono