[quote name='EOSHD' timestamp='1344776311' post='15393']By the way it isn't so much 24p at 24Mbit which is the problem on the FS100 but 60p at 28Mbit, because bitrate is allocated variably per frame. The more frames the more the available data is thinly spread across them.
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That's not correct. With Mpeg4, practically all redundant data over time are reduced. The lower the frame rates, the more radically the content alters from frame to frame, so you'd have less redundant information and need higher bit rates. For 120 fps, you'd need about 30 mbps. Ever did stop motion animation? You only draw the changes, and what changes between two frames of 48 fps is a fraction of what changes between two frames in 24 fps in the first place. In hand-drawn animation, you'd simply draw a few motion blurred objects connecting the key frames, no matter how many phases the frame rate actually demanded.
What about camera movement, when [i]every[/i] pixel has changed position in the next frame? That used to be my argument, but the engineers' answer is: If the position changing is predictable, it is a classic motion path, which doesn't even need particularly high bit rates. If it is chaotic ("stressing the codec"), the encoder tends to simplify the details, which by their nature then cannot be recognized as details by the human eyes.
Noise, though not detail, is not only redundant. We perceive noise subconsciously as a natural phenomenon. Watch the shadows below your desk in the evening. Are they dead?
That's why too low bit rates are a problem - at any frame rate: They iron out the random noise. With 60p you [i]always[/i] see this effect, with or without interframe. That's because you have more than twice the temporal resolution. 24p is a very effective way of temporal compression. As little as possible, as much as needed.