Didn’t know if anyone else has experienced this or knows this: I recently began playing a standard avi movie from my hard drive hooked up to my WDTV Live Plus. I had a better HD copy and wanted to replace the current movie. The HD copy was on my laptop so I paused the standard movie and transferred the HD copy over my network to the hard drive hooked up to the WDTV. Since this was going to take awhile (I have cable internet running 54 Mbps and the WDTV is hardwired using a Linksys powerline system) _ I started watching YouTube videos…yes on the WDTV while uploading over the network. _
Once the upload was done (25 min or so), I selected the new HD file (which was renamed to the same file name as the old one) for playback. I deleted the old file BTW. The choices came up asking me if I wanted to ‘restart’ or ‘resume’ playback. Interesting. I selected ‘resume’ and the movie began at the same point as the old one but it was in HD! 
Now I tried this again with another movie and became worried when I received an error trying to play the ‘new’ file but I went back to the home screen which allowed the WDTV to rescan the attached server and it worked! What’s interesting to note is that the old file was classified as .avi and the HD file was .mkv.
Just thought I’d share this and I’m liking my choice to buy a WDTV Live Plus more and more! I even picked one up for my 71-year-old father and he loves it! :manhappy:
