The iPad supports a variety of video formats, including MPEG-4, H.264 and MOV. However, if you're trying to play a file that's not supported by the iPad or has been corrupted, it may not work.
The iPad supports the following video formats:
• MPEG-4: MPEG-4 files have the .mp4 extension and can be used for high definition playback.
• H.264: The iPad can play H.264 files with the .mov extension.
• Motion JPEG: Motion JPEG files have an .avi extension and are used for standard definition playback.
If you want to play a non-supported video file on your iPad, you can convert it to one of these formats using third party software -- just be aware that there may be some quality loss during this process