[mdlug] Best Linux rig for capturing frames from analog video?

[David F]

On 05/25/2013 02:50 AM, Michael Mikowski wrote:
> Thanks Aaron, that was my guess too (see my earlier post).  A digital cam would also reduce complexity and improve reliability.

In some cases I would agree, but be careful -- it depends on the application 
(which the OP didn't really specify).  Cheap USB web-cams sometimes don't 
have good temporal resolution (i.e. low exposure time, avoiding 
motion-blur): they're typically intended for video web-chat where the 
subject doesn't move much or fast.  In some cases, a decent NTSC analog 
might do better (and capture cards can be had for cheap [1]); or the hacked 
point-and-shoot will deliver much higher-quality images.  Also, if the 
camera cannot be physically close to the host system, you will have some 
problem-solving to do regarding the maximum length of the USB spec.

I think the typical "IP camera" is a camera (lens+sensor) attached to a 
small SoC (possibly running Linux); the quality of the camera will determine 
the quality of the images, and obviously IP can travel arbitrary distances. 
  If you don't want to deploy a PC-style system at the location of the 
camera, something similar (possibly better) could be created by the hobbiest 
using a USB-cam and a Rasberry Pi, home router with USB port and OpenWRT 
burned, etc., which could then communicate over IP, overcoming the distance 
issue and placing much (or all) of the intelligence and/or storage on-board 
the embedded system; but the cost and hassle might add up quickly to make a 
manufactured IP camera an easier solution, if less customizable.

For image capture on a Linux system, most software (e.g. motion, mentioned 
by the OP), whether for USB cams or analog-to-digital cards, is built on top 
of video4linux (V4L2) [2].  Depending on the application, for a more elegant 
solution than a script that runs a CLI like motion and then mucks with 
dumped image files, choose any scripting language with bindings to V4L2 (or 
just use C/C++) and make the captures yourself, then process as desired. 
Furthermore, mencoder (mentioned by the OP who called it "crude," though I'd 
like to see that defined, don't understand what he meant) can capture 
directly from V4L2, or can be used to encode video from multiple still image 
files.

-- David

[1]: E.g. newegg has this one for $17.99 including shipping, which works 
with Linux:
http://www.newegg.com/Product/Product.aspx?Item=N82E16812156023
NB: it's just the first one I found, not an endorsement, search for others 
if serious about purchasing and check for compatibility with V4L2 at:
http://linuxtv.org/wiki/index.php/Hardware_Device_Information

[2]: http://linuxtv.org/