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576p refers to progressive video encoded in frames 576 pixels tall. 576p is generally used for video from film sources, as they're natively progressive. It can also consist of progressive video or interlaced video that's been deinterlaced for a number of possible reasons. Most 576p video comes from either DVD or deinterlaced TV captures.
In addition to captured PAL , other common formats using 576p video are Standard Definition DVB, EDTV, DVD, some DV, and SVCD. 576p is most suitable for video formatted to play on a progressive scan Digital TV (DTV) of some kind.
Regardless of the format it's encoded in, or exact resolution of a 576p video file, they almost always have a framerate of 25fps to match PAL.
Digital Video Fundamentals - Resolution and Aspect Ratio