On Wednesday 20 August 2003 10:03, dmitriy wrote:
> Hi all!!
>
> Tell please, whether there is a software for detecting movement? I have
> written to the list motion.sourseforge.net of dispatch and have received
> the answer, that their software product processes the image with the
> help only the processor. But I have a device which can digitize video
> without the help of the processor. Thanks for the answer!

At one point or another, you need the uncompressed images, as there is no way 
to determine the difference between two compressed jpeg images.

The simplest way is to get uncompressed images from the grabber, compare them 
and compress the ones you want to keep in software. This is how Motion does, 
but that leaves the compression hardware idle.

A more complicated way could be to let the card grab, compress and save every 
frame into short files. I'm not sure whether the modern time-limit argument 
is in seconds or frames, but let's say it's in seconds;

Make lavrec save into files that are one minute long. Combine, provided that 
the respective licenses permit that, code from lavplay, for reading and 
decoding frames, with code from Motion, for movement detection, and code from 
lavrec, for saving frames into a file, and have this new program throw away 
all equal frames and keep those that are not equal, saving them in their 
original, undecompressed form, into a new file.

This would make the motion detection a post-processing filter that you can 
apply to an already captured stream. The main drawback is that it would 
detect movement with a minute's delay, or so.

The third option would be even more complicated and possibly more unstable; 
build all that above right into a modified lavrec, and decompress, compare 
and detect in realtime.

In short; no, I don't think there's any motion detector for MJPEG streams 
available. Be the first to create one! :)

/Sam



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