I have successfully followed the excellent tutorial on reformatting already (thank you!) and I put back the wmas and the amv that came with the player; then added some mp3s I'd made and an amv I made that I had tested on an amv player. Everything worked fine and clear except for the amv I'd made. My player is a 470MB knockoff that looks like this
http://www.gba-flash.com/images/mp4%20zv100.jpg without the arrow in the center and with a circled V (like visual land brand) and the number VL-537 printed on front.
I have already made a copy on my computer of the working amv that came with the player. Is there any on or offline software that will examine it and tell me what resolution, screen size, codec or whatever I need to implement in making more?
Thanks for everything -- especially this site and the contributions everyone makes to it.