MPG which typically incorporates MPEG-1 or MPEG-2 audio and video compression, can't be played on iPad, iPhone, for Apple devices only support some special formats like MP4. And people can't import MPG files to iMovie, too, because iMovie should be able to import MP4 files with no issues. MPEG-1 files can be a problem if they're muxed, which it probably is. MPEG-2 files are a problem usually as well.
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convert wmv to m4vconvert avi to flv