The issue seems to be with the output signal from the IR camera I am using. The tv.capture function worked fine using an Iduino UNO when I used a high quality DVD player as the video source.
When I compared the video signals of the IR camera and DVD player using an o-scope, it showed that the timing was slightly different. I tried changing the [#define _NTSC_TIME_SCANLINE 63.55] value in the video_properties.h file and that didn’t seem to help. I then experimented with the value of ‘W’ in the main program. It was 128 originally, and I found that I could get the IR camera to work if I lowered that value to 119 or less.
I was hoping to find the source code for tv.cature in order to see how all the parameters in the video_properties.h file were used, so that I could make an intelligent change to the timing in the tv.capture file. I was unable to find what I was looking for- what did I miss?