# What Is The Frame Rate Of ATSC broadcasts?



## no. 5

I thought that high definition broadcasts used a frame rate of 30fps, like NTSC, but from a few passing references, it looks like ATSC broadcasts are at 60fps. But after some looking around, I have not yet found much of any information as to what frame rate is used for ATSC.

Sooooo, my question is; what frame rate are 720p and 1080i high definition television broadcasts?


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## bobgpsr

I understood that ATSC has 1280x720p60 (60 frames per second -- progressive) and 1920x1080i60 (30 frames per second via 60 Hz interlaced fields -- interlaced) formats that are in common, over the air, broadcast use. Other sizes and frame rates (including 24 frames per second) are in the ATSC standard but not currently in use. Fox and ABC tend to use 720p60 while NBC, CBS and PBS use 1080i60.


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## no. 5

Ahh, thanks bob.

So that would mean that the '60' in 720p60 and 1080i60 means how often the picture (or part of the picture) is refreshed, not the frame rate?

If anyone has links to that part of the ATSC spec...


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## gsmollin

The frame rate for 720p is 60/second. The frame rate for 1080i is 30/s. The "p" spec uses progressive scan, so each new frame is complete with a 60/s rate. The "i" spec uses interlaced scan so each frame is constructed from two fields, each sent 60 times/second.

The picture information is compressed using mpeg2. Each frame, or field is not unique, but is encoded as a difference from the previous frame or field. At regular intervals a key frame is sent which is complete. This re-synchronizes the transmitter and receiver.


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