Let me offer some observations about the question of a "best" frame rate setup. To do that, I'm first going to lay out some rather lengthy background. It will be review for some (most?) of you, but I think it's important to cover.
For about 100 years, the standard for film content has been that it is shot and projected at 24 frames per second. Televised video content (in the United States and other NTSC countries) was 30 frames per second, broadcast as 60 interlaced fields per second. Since home displays were originally for television, they were built around this 30frame/60field standard. To be able to broadcast filmed content on television (and later to sell videotapes and DVDs), it was necessary to convert 24fps film to the 60 fields per second that a TV could display. This was done by a process called "telecine" or "
3:2 pulldown."
If film was 30fps instead of 24, you'd just take each film frame and slice it up into the odd and even interlaced fields, and your job would be done. But since 24 doesn't go into 60 evenly (60/24 = 2.5), what ends up happening is that sometimes you create two fields from a frame, and sometimes you create
three, in an alternating cadence. When HD came along with support for 60 full progressive frames per second, this process was just extended so that you got an alternating sequence of two or three display frames (not fields) for each film frame.
This whole process works pretty well, but there's a notable artifact caused by the fact that some film frames are displayed longer than others: judder. This is a sort of unevenness in the motion that's visible when the action or camera moves in certain ways, and while it could be distracting, at first it was a largely unavoidable necessity to be able to display filmed content on a TV.
This started to change with the advent of Blu-ray Disc, which was the first home medium to support storing content in its native 24fps format. At first (and for a long time), TVs didn't accept 24fps input, and so even though the disc had 24fps content on it, the player had to do this 3:2 pulldown process internally to give the TV what it could accept. But once TVs and projectors started to natively refresh their panels at 120Hz (which is an even multiple of both 60 and 24), it became possible for a TV to accept 24fps content and display it very smoothly by simply showing each individual film frame across five display refresh cycles. So, once you had a TV that could handle it, you could just set your Blu-ray player to allow 24p output, and you'd get rid of that judder.
And this brings us to Kaleidescape. Unlike Blu-ray players and most other source devices, Kaleidescape uses extensive animation in our user interface. Animation looks best at a high frame rate, and Strato runs its onscreen display at 60 frames per second to give the smoothest possible animation. But this creates a conundrum: should we switch the output from 60 to 24 when starting playback of film content? Or should we convert to 60?
It turns out that this is a complicated question. Some displays will quickly and smoothly switch between frame rates, such that it's virtually unnoticeable. Other displays, and especially display
chains (including audio and/or video processors, matrix switches, etc.) may take many seconds to respond to a change in frame rate, and during that time, you lose picture and sound at best, or see weird colored flashes at worst. So for many years we've provided the option to minimize display mode changes (accepting a little judder to avoid the signal loss), or allow display mode changes (when the display handles it well). Now we've added this third option, which is to accept degraded OSD animation in exchange for no signal loss
and no judder.
And this is where I want to introduce the final wrinkle. It turns out that a number of displays and projectors include processing called "inverse-telecine," or "cinema mode," or any of a number of other variations. This processing relies on the fact that if you can detect that a 60fps signal was really originally a 24fps signal that has gone through 3:2 pulldown, you can employ a little bit of math and a little bit of video memory, and you can
fully and losslessly recover that original 24fps source content. And then once you've done that, you just frame-quintuple it as you would have if you had gotten a 24fps signal over the HDMI port.
If the display's 3:2 pulldown detection is solid, and the inverse-telecine implementation is solid, then you can have the best of all worlds. You can have 60fps, smooth animation from the onscreen display, and you can have judder-free playback of film-sourced content, without the signal disruption of a frame rate change.
When I had a Sony 1100ES projector, its inverse-telecine was
almost perfect, but not quite. I would get occasional stutters that were distracting enough that I opted to send it 24fps output for film content by setting my Kaleidescape player to allow display mode changes. Fortunately, the 1100ES was also pretty quick at responding to frame rate changes, and so this wasn't a great hardship, but it did produce 5-8 seconds of black screen when starting a movie.
My 995ES seems to have a flawless inverse-telecine implementation. I have never seen an artifact caused by it, at any rate. So I have now changed my players to output 60fps ("Minimize display mode changes"), and I have both 60fps animation and judder-free playback with no startup delay.
This long-winded diatribe is intended to explain why there is really not a one-size-fits-all answer to the question of which is the "best" frame rate setup. It depends completely upon the specifics of all of your connected equipment, and your own sensitivity to things like judder or delays in video/audio lock when starting and stopping playback. Don't assume that setting "Minimize display mode changes" is going to produce a compromised experience versus the more "pure" option of allowing display mode changes. It may not, if you have good inverse-telecine available to you. If you don't have good inverse-telecine available, and if display mode changes produce an unacceptably long loss of signal, then the option of running the OSD at 24fps may be the best choice, even though the OSD animation will suffer a bit.
