When I publish a .mp4 file to my blog, it will play fine on my computer but not on an iphone or ipod touch. When I place this same .mp4 file on a separate web server, it plays fine on both the computer and iphone/ipod touch which means the file is ok. You can test this out on my older wordpress site at
http://www.tomsextro.com
I have tested this with the latest wordpress site and it doesn't work either. Any ideas?