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DougJrS
Jan 31, 2008, 08:22 AM
The "old" Apple TV only supported output at 720p. Durning MWSF it was talked about as being able to show DVD quality or HD quality. Since a DVD in NTSC format is 720480 it would now seems that Apple supports an HD format that is different then 720, so is it 1080?

Doug



DougJrS
Jan 31, 2008, 08:36 AM
I found the following specs on Apple.com... Guess I didn't look hard enough the first time.


So, now I am really confused as to what the difference is in DVD and HD quality...



Video formats supported
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

iTunes Store purchased video: 320 by 240 pixels, 640 by 480 pixels, 720 by 480 pixels (anamorphic), or high-definition 720p

MPEG-4: Up to 3 Mbps, Simple Profile with AAC-LC audio up to 160 Kbps (maximum resolution: 720 by 432 pixels at 30 fps) in .m4v, .mp4, and .mov file formats

ibelyias
Jan 31, 2008, 08:51 AM
So, now I am really confused as to what the difference is in DVD and HD quality...


DVD Resolution: 720x480

HD Resolutions:
720p: 1280x720
1080p: 1920x1080

The higher resolution moving images means a higher quality picture. HD imagery is considered 720p or 1080p. AppleTV does not support 1080p (believe me, I found out the hard way), but it does support 720p, which is still HD-quality, though at the lower end of the HD-spectrum.

ibglowin
Jan 31, 2008, 08:54 AM
But,

It will upscale to 1080i. My TV will not accept a 720P signal, it will downscale it to 480P. I have my :apple:TV set to 1080i.

err404
Jan 31, 2008, 09:30 AM
It's my understanding that for content that it under 30 frames per second, 1080i when displayed on a 1080p screen, is in fact shown progressively (full 1920x1080 frame at 30fps).

This is due to the 1080i spec being at 60fps with each full frame being sent as a pair of half resolution (1920x540) frames. A 1080p screen will wait for both halves and then display them merged together into the original full 1920x1080 frame.

While this is fine for movies and tv shows, true 1080p sources can have twice the frame rate (60fps).

Note- This only applies for 1080p displays

Now that said, can the apply TV fake 1080p 30fps in this manner? The hardware is certainly capable of it if it can upscale content to 1080i (unless it has a dedicated scaler chip to off load the work). The issue would seem to be if the device can handle decoding the extra bitrate in the file.

Before you say it, yes I know that apple says it is only able to support 720p, but that could be because they have no intention of selling higher in iTunes.
Case in point. Apple claims the iPhone can support a max of 640x480 at 1.5 mbit per second, but in reality it can go quite a bit higher. I have used 720x480 at over 2mbit per second (33% higher datarate).

Avatar74
Jan 31, 2008, 11:06 AM
The "old" Apple TV only supported output at 720p. Durning MWSF it was talked about as being able to show DVD quality or HD quality. Since a DVD in NTSC format is 720480 it would now seems that Apple supports an HD format that is different then 720, so is it 1080?

Doug

DVD: 720 x 480 = 480p; not 720p

HDTV: 1280 x 720 = 720p

HDTV: 1920 x 1080 = 1080p

HDTV (interlaced): 960 x 540 (alternating fields) = 1080i

mr_matalino
Jan 31, 2008, 11:11 AM
It's my understanding that for content that it under 30 frames per second, 1080i when displayed on a 1080p screen, is in fact shown progressively (full 1920x1080 frame at 30fps).

This is due to the 1080i spec being at 60fps with each full frame being sent as a pair of half resolution (1920x540) frames. A 1080p screen will wait for both halves and then display them merged together into the original full 1920x1080 frame.

While this is fine for movies and tv shows, true 1080p sources can have twice the frame rate (60fps).

Note- This only applies for 1080p displays

Now that said, can the apply TV fake 1080p 30fps in this manner? The hardware is certainly capable of it if it can upscale content to 1080i (unless it has a dedicated scaler chip to off load the work). The issue would seem to be if the device can handle decoding the extra bitrate in the file.

Before you say it, yes I know that apple says it is only able to support 720p, but that could be because they have no intention of selling higher in iTunes.
Case in point. Apple claims the iPhone can support a max of 640x480 at 1.5 mbit per second, but in reality it can go quite a bit higher. I have used 720x480 at over 2mbit per second (33% higher datarate).

I don't think this works. There is big difference between 720p and 1080p (file size alone). The only way (I think) to upscale it is if you could upscale it at your receiver. Even then I'm not sure if you get a 1080p picture. The only way I know to get a true 1080p picture is with a blu-ray/HD-DVD player/movie and a 1080p TV.

nutmac
Jan 31, 2008, 11:33 AM
DVD: 720 x 480 = 480p; not 720p

HDTV: 1280 x 720 = 720p

HDTV: 1920 x 1080 = 1080p

HDTV (interlaced): 960 x 540 (alternating fields) = 1080i
That's not quite right. 1080i (1920x1080 interlaced) is not the same thing as 540p (960x540 progressive). Although 1080i does have 960x540 chroma resolution, the full resolution for a single field is 1920x540.

tfast
Jan 31, 2008, 12:15 PM
The main thing to think about is frame size and frame rate.

1280x720 = 921,600 pixels per frame.
1920x1080 = 2,073,600 pixels per frame.

A 1080i signal running at 30 frames per second has about the same amount of data throughput as a 720p signal running 60 frames per second. These are the standard signals the Networks broadcast at - 1080i 30fps (interlaced) and 720p 60fps (progressive).

Where it changes is native frame rates. Movies are at 24 frames per second and QuickTime runs them at 24. Therefore a movie running at 1080p24 is twice as large as a movie running at 720p24.

I'm not sure what the AppleTV specs are, but if they were 720p, I'm going to bet they will stay that way. A 1080 AppleTV would have to have the capacity to send twice as much data. A software upgrade doesn't generally fix a data rate issue, otherwise they would have just started at 1080p and sold it that way.

Avatar74
Jan 31, 2008, 03:00 PM
That's not quite right. 1080i (1920x1080 interlaced) is not the same thing as 540p (960x540 progressive). Although 1080i does have 960x540 chroma resolution, the full resolution for a single field is 1920x540.

I stand corrected. Just for clarity though... when you're talking chroma are you referring to an HD signal sent as component (YPbPr, two chrominance channels and one luminance) or RGB?

If you're talking component signal... I can't remember... is it 4:4:4:4 or 4:2:2 color space? There's a big difference in the broadcast signal bandwidth between the two (chrominance subsampling, etc.) and I'm not all that versed on how decoded H.264 or MPEG-2 come through to the display when decoded at the converter box or HD/BluRay DVD player.

err404
Jan 31, 2008, 03:38 PM
I don't think this works. There is big difference between 720p and 1080p (file size alone). The only way (I think) to upscale it is if you could upscale it at your receiver. Even then I'm not sure if you get a 1080p picture. The only way I know to get a true 1080p picture is with a blu-ray/HD-DVD player/movie and a 1080p TV.

Thats not entirely true. On a 1080p display*,1080i content at 24fps is pixel for pixel and frame for frame identical. There is literally no difference. This isn't really upscaling, as no scaling is required. Since a progressive screen can not display an interlaced image, the display waits for 2 frames to come in where they are displayed simultaneously as a single frame (odd line from one frame, even from the other). The question is really whether the apple TV has the horse-power to push out 1080i at 50-60fps.

did you know sony's first 1080p display only excepted 1080i input for just this reason?

BTW- i am not suggesting that 1080i is as good as 1080p. For gaming and future media, the 30fps limit of interlacing is a big deal. However today film content doesn't exceed this rate, making 1080p little more then a marketing phrase for BD and HDDVD.

*a few very poor quality 1080p displays will just thorw out the second fame and double the lines of just one field. but this is not common.