QUOTE(Spaceman2004 @ Mar 7 2007, 03:09 PM)
I'm not sure the xbox is up to it anyways.
If the xbox can ouptut 720/60p then I'm pretty darn sure it can output 720/50p & 720/48p (actually 47.952 fps). Don't know about 72hz but 48 would still be much better for 24 fps material.
QUOTE(sheepie @ Mar 7 2007, 06:45 PM)
what do you mean by stutter?
A small excerpt from the lengthy wikipedia article that deals with the telecine process.
The process of converting 24 frame/s material to 29.97 frame/s is known as 3:2 pulldown. The term "pulldown" comes from the mechanical process of "pulling" the film down to advance it from one frame to the next at a repetitive rate (nominally 24 fps). This is accomplished in two steps. The first step is to slow down the film motion by 0.1%. This speed change is unnoticeable to the viewer, and makes the film travel at 23.976 frame/s.
The second step of the 3:2 pulldown is the 3:2 (or 2:3, see below) step. At 23.976 frame/s, there are 4 frames of film for every 5 frames of NTSC video:
These four frames are "stretched" into five by exploiting the interlaced nature of NTSC video. For every NTSC frame, there are actually two complete images or "fields," one for the odd-numbered lines of the image, and one for the even-numbered lines. There are, therefore, ten fields for every 4 film frames, and the telecine alternately places one film frame across two fields, the next across three, the next across two, and so on. The cycle repeats itself completely after four film frames have been exposed, and in the telecine cycle these are called the "A," "B," "C," and "D" frames, thus:
This is how 480/30i & 1080/30i video is displayed by XBMC for NTSC users. As you can see the process of making 5 frames from 4 results in 2 of those frames looking like garbage. In progressive mode (480 & 720p/60) instead of garbled frames, each frame is repeated twice but one in four frames is repeated four times eg.
A B C D at 24fps
A,A,B,B,C,C,D,D,D,D at 60fps
When the camera is panning this is especially noticeable as the duration of one in four frames is twice that of the three proceeding frames. As this actually occurs 12 times a second it causes what would originally be a smooth pan at 24 frames per second to stutter quite badly when converted to 60 fps. If the xbox allowed 48hz output (or 72 if possible) then each frame of a 24fps movie could be repeated twice (or 3 times for 72hz) and there would be no garbled or superfluous frames. This is the sort of thing that home cinema freaks specifically use HTPC's or expensive scalers to reproduce and would be a massive feather in the cap[ of XBMC if the kernel could be enabled to allow it.
The same thing is happening to PAL users who wish to use XBMC to upscale DVD's. Our native frame rate is 25fps which is close enough to 24 fps that no repeating of information (or stuttering )is necessary. Our video is simply sped up by 4% and maintains the exceptionally smooth movement of its cinema cousin. As the xbox only recognises 60hz HD modes instead of our native 50 hz (where each progressive frame at 25fps would be repeated twice) we get 60hz instead and this means repeating 1 in 5 frames causing all the same problems that have been explained above. Due to massive complaints microsoft enabled 50hz HD output when using 50hz DVD or HD DVD on the 360 in the Autumn 1080p kernel update but, for some reason, didn't bother to enable 71.928hz for you NTSC users to get silky smooth film-like playback from NTSC material.
We all know what a great bit of kit the xbox is and XBMC absolutely wipes the floor with the crippled media capabilities of the 360. Given the way that it has been cracked open to such a great extent it would be great if this feature of flexible frame rates to match 24 or 25fps could be enabled as it would be a massive feather in XBMC's cap. Full blown scaler capability. At the moment 60hz doesn;t do anyone any favours, where ever you're from.