Not exactly. Usually when you are dealing eith it on a computer, it will be 30fps (29.97 fps, or frames per second) but that is only because most decoders de-interlace the video. Essentially everything recorded for TV through the 90s, and most things recorded for TV today, are recorded interlaced. In reality, this means the video is 60fps at half height.Pneuma said:I talking about broadcast TV, which is NTSC format in the US. Thus, 30fps.
A regular NTSC broadcast viewer will typically have a display that is about 640x480 (ignoring overscan, the fact it is an analog broadcast, etc, but easier for the sake of argument). It first displays a 640x240 picture, starting with the first line and then displaying using every other line (1, 3, 5...639). Then it displays a second 640x240 image starting at line 2 and usinge every other line (2, 4, 6...640).
The key here is that with the exception of High Definition recording, all recording for TV is done at about 60fps, so the first part of an interlace image will be recorded 1/60th of a second from the second part of the image, which in turn is recorded 1/60th of a second from the first part of the next image. So yes, it really is recording/display at 60fps (60 Hz/1.001 fields per second). And due to the way interlacing is interpreted by the brain, it will display a moving object smoother than 480p @ 30fps.
The first difficult arises with computers, which haven't been designed around interlaced signals as their primary output in almost two decades. They will take the two parts of an image, blend the lines together to reduce jagged edges from moving objects, and display it as a single frame at 30fps.
The second difficulty is that increasingly more content is recorded in a high definition progressive format that takes all of the rows at once instead of alternating. When 480P@30fps is transmitted over NTSC, you are doing 30fps, but drawing it in a wierd way. It is the same for pretty much any other HD recording formats.
Film is recorded in 24fps progressive, so to get it to display on an NTSC dislay, they do all sorts of evil things that should never be brought up like forced field flags or actually encoding it as interlaced content. For PAL, they usually just speed things up by about 4% to have it match framerates.
Most NTSC CRT displays will display NTSC as 60fps interlaced. Most fixed pixel displays (plasma, LCD, etc) will deinterlace and display at 30fps.
So yeah, any old NTSC content is 60fps, a lot of new (and progressively more) content is 30fps, and movies are 24fps.