Output 24p?

Afraid not.

Wouldn't be much point really without source material at 24 fps, and if you changed the frame rate of any existing content it would probably look worse.

AC

Message was edited by: Alley_Cat

I know movies are filmed at 24fps.

Unfortunately not being in the USA I cannot currently rent/purchase movies from iTunes Store to tell you if that's how they're encoded or not. I've assumed they're not, but it does depend on how they're encoded in the first place and the frame rate of the source which may or may not be the original 24fps.

Even if they're encoded at 24fps (which would be nice), AppleTV will not output 24fps only PAL/NTSC rates which would suggest some frame interpolation on the fly which will not be ideal.

AC

By the way, no harm sending feedback requesting a 24fps mode to:



http://www.apple.com/feedback/appletv.html

AC

Message was edited by: Alley_Cat

Given the specs for AppleTV video:

H.264 and protected H.264 (from iTunes Store): Up to 5 Mbps, Progressive Main Profile (CAVLC) with AAC-LC audio up to 160 Kbps (maximum resolution: 1280 by 720 pixels at 24 fps, 960 by 540 pixels at 30 fps) in .m4v, .mp4, and .mov file formats

it's possible that HD is encoded at 24fps, however it's still going to output at 50/60Hz depending on your output setting.

AC

The frames per second count and the refresh rate are not the same thing.

The tv has output modes of 50 and 60 Hz and your tv/projector likely only supports these refresh rates. I doubt the current tv model could support different refresh rates and in any case I doubt there would be much point, tv's with alternative refresh rates are still a rarity and indeed the market place for these types of tv's is likely made up from people who expect a much higher quality than that provided by the tv.

Although the refresh rate and frame rate are independent of each other, the ideal situation would be one where the refresh rate was a multiple of the frame rate, in the case of content encoded at 24p this is achieved in high end equipment by having a refresh rate of 120 Hz (not 24 Hz)

When the refresh rate is not a multiple of the frame rate, there are a number of techniques that can be implemented in a device. Pull down is a common technique used in many video players for example.

In the case of an NTSC device this is achieved by 3:2 pull down which enables the 24 progressive frames in each second from the source material to be played as 60 interlaced frames each second, thereby maintaining the same timeline for the output.

In the case of PAL a similar method can be used to play 50 interlaced frames from 24 progressive frames and maintain the timeline as before. However this method is not commonly used for PAL content and instead 2:2 pull down which results in the 24 progressive frames being played as 48 interlaced frames is more commonly used.

As you can see this leaves 2 interlaced frames each second unused which are filled by the first of the next seconds 24 progressive frames. This of course makes the content play slightly more quickly than it should, this difference is generally unnoticeable in terms of video but can sometimes be detected in the audio by the very perceptive.

I don't believe the tv uses pull down to maintain the timeline, it can play content using any number of frame rates and would need different pull down ratios for each frame rate and for both 50 Hz and 60 Hz output modes.

It clearly doesn't use the technique of simply adjusting the contents duration, while this is acceptable for 24 fps at 50 Hz it would be substantially obvious if you played content encoded at say 12 fps.

Another technique would be to use vertical sync, to lower the frame rate to match the refresh rate of the output mode. Again I don't believe this is used in the tv, I might be wrong but I would think it would be noticeable.

What I suspect happens with the tv is that it simply plays content at it's proper rate and allows the picture to 'tear' when this doesn't match the refresh rate.

This may well seem like a crude approach to the issue but it may actually be the only reasonable solution to it. My personal feeling here is that tearing is far less noticeable than the jerkiness which results from pull down or the lower frame rates as a result of using vertical sync.

So in answer to your question the tv does (most likely) output your 24 fps content at 24 fps, what it doesn't do is output at 120 Hz, but does this matter, I suspect not since I suspect your projector couldn't support it even if it did.

Voix wrote:
My projector supports a refresh rate of 24p.

No such thing as a refresh rate of 24p

Makes no sense why AppleTV would convert 24fps to a 60p signal when it isn't necessary and degrades image quality.

It doesn't convert 24 fps to 60p at all, it doesn't convert anything, it plays your 24p files at 24 fps and it outputs it at either 50 Hz or 60 Hz.

If you want to output at 120 Hz to avoid tearing, go buy a blu-ray player that outputs at 120 Hz, personally I wouldn't want to pay twice as much for an tv to do something that an insignificant number of people will make use of.

Winston Churchill wrote:

Voix wrote:
My projector supports a refresh rate of 24p.

No such thing as a refresh rate of 24p

http://en.wikipedia.org/wiki/24p
http://www.projectorcentral.com/panasonic_ax100.htm

It's all just becoming a minefield for the average consumer to understand all the technicalities IMO. HD Ready was bad enough, now all these varying methods of displaying 24 fps on plasmas/LCDs/projectors confuses the **** out of me.

AC

http://hometheater.about.com/od/televisionbasics/qt/framevsrefresh.htm

"In other words, even with higher refresh rates, there are still only 24 separate frames displayed every second, but they may need to be displayed multiple times, depending on the refresh rate.

To display 24 frames per second on a TV with a 120hz refresh rate, each frame is repeated 5 times every 24th of a second.

To display 24 frames per second on a TV with a 72hz refresh rate, each frame is repeated 3 times every 24th of a second.

To display 30 frames per second on a TV with a 60 hz refresh rate, each frame is repeated 2 times every 30th of a second.

To display 25 frames per second on a TV with a 50 hz refresh rate (PAL Countries), each frame is repeated 2 times every 25th of a second.

To display 25 frames per second on a TV with a 100 hz refresh rate (PAL Countries), each frame is repeated 4 times every 25th of a second."

Not sure whether you are agreeing or disagreeing with me, however for the avoidance of doubt what I'm saying is that 24p refers to a progressive frame rate, it's not a refresh rate. I suppose you could have a refresh rate of 24 Hz, but that's not the same as 24p.

In actual fact I doubt there are any or not so many devices with a refresh rate of 24 Hz, this frequency is too low and would suffer with flicker, I believe there are displays with refresh rates of 96 Hz but more commonly I would expect 120 Hz which is both a multiple of 30 fps and 24 fps.

Thanks Jeff - that was my understanding of how things worked.

AC

Just saying that 24p is a recognised entity, but agreeing that fps of the source and refresh rate of the device are different.

For raster based displays I can understand flicker at low refresh rates, but I suspect it's less critical for other devices for equivalent fps.

The projector link implies that the OPs projector may be able to actually output 24fps with a refresh rate of 24 Hz.

Trying to recall if my old Super 8 projector I had as a lad had much flicker!

In my mind, for non-raster displays, I can't quite see how having repeated identical frames is necessarily less flickery than say 1 frame held for the same duration as 3 shorter ones given similar blanking times between frames.

The other problem is all the pseudo 24p compatible modes on modern TVs - one of the new Panasonic plasmas has a 24p feature that when you actually think about it interpolates every single frame and never shows the original!!!!

AC

It's not really clear whether it uses 24 Hz or a multiple thereof from that article, the issue being that the human eye can detect less than 30 images per second, even in old cinemas where film was used each frame was shown twice and sometimes 3 times.

However the article hits the nail on the head here when it says "The 1080p/24 format is important because it will become a standard feature on many of the new high definition DVD players, HD-DVD and Blu-ray. Indeed, a couple of the Blu-ray players scheduled for release next month already have it."

TV's supporting true 24 fps playback are still a long way off being a common occurrence and are more like toys for videophiles at this time, but more importantly anyone buying this type of equipment is unlikely to be in the market for a device that plays movies at 720p and less than 5 Mbps.

It strikes me the OP has either bought this projector without any real knowledge about the technology they are buying, which I suppose people do from time to time or they are simply letting everyone know what they have. Personally I think if you're going to be buying this sort of equipment you should at least know that you need specialised equipment to feed it.

Winston Churchill wrote:
It's not really clear whether it uses 24 Hz or a multiple thereof

Kind of suggests it can then talks about 24Hz multiples, I agree not entirely clear.

However the article hits the nail on the head here when it says "The 1080p/24 format is important because it will become a standard feature on many of the new high definition DVD players, HD-DVD and Blu-ray. Indeed, a couple of the Blu-ray players scheduled for release next month already have it."

The marketing people are going to lap this sort of thing up aren't they!

TV's supporting true 24 fps playback are still a long way off being a common occurrence and are more like toys for videophiles at this time, but more importantly anyone buying this type of equipment is unlikely to be in the market for a device that plays movies at 720p and less than 5 Mbps.

If you look at the new range of Panasonic plasmas most seem to 'offer' a 24p mode of some kind, but the implementation (compromises!) vary at different price levels, and as I said there's one implementation that seems to never even show the original frame only a derivative of it as all frames are interpolated - that sounds awful!

It strikes me the OP has either bought this projector without any real knowledge about the technology they are buying, which I suppose people do from time to time or they are simply letting everyone know what they have.

Miaow 😉

Personally I think if you're going to be buying this sort of equipment you should at least know that you need specialised equipment to feed it.

You have to read all the small print, make no assumptions and ask appropriate specific questions in the face of glowing marketing write-ups for most devices these days. In general if it sounds too good to be true it usually isn't!

More and more these days I'm quietly bemused when people tend to throw the toys out of the pram as some cutting edge feature hasn't been implemented on their new toy, as though it's the end of the world or something - 'OMG such and such *****' as it doesn't support an as yet unsusable HDMI revision seems the commonest.....Perhaps I used to be a bit anal about that of thing in my younger days, but as you get older and more cynical...

AC