Recorded video visible on device, but not other media players once uploaded When I record videos with the rear-facing camera on my Archos 43 Internet Tablet, I am able to watch those recordings on my device, but when I attempt to upload them to online video sharing sites like youtube or blip.tv, they aren't properly recognized or converted.  Likewise, when I transfer them to my computer, I can't play the video file correctly.  If I transfer the file back to my device, it plays just fine.

I know that the device produces *.mp4 video files.

How can I convert these (corrupted?) videos so that I can see them on my computer and upload them to video sharing sites?

Thanks.
MP4 is a container that can contain different video codecs, it sounds like your device is creating its videos using an unusual codec that not many other devices have loaded by default. As Seth and Hcpl have said VLC Player can play almost any format and should be able to play your videos.

If you want to know what codec is being used, then try opening the video in a codec identifying app like GSpot, this should tell you exactly which audio and video formats and codecs are in your videos.