Blu-Ray Players & HD TVs

Hi,

A couple of basic questions from someone that does not yet have Blu-Ray. Hope you can help me understand how this works.

1. If you have a 720i or 720p encoded Blu-Ray disc and a 1080i or 1080p capable TV, do Blu-Ray players up-convert automatically to 1080, play it at its 720 native resolution, or is this something the user is allowed to choose?

2. Also, if you have a 1080i or 1080p encoded Blu-Ray disc and only a 720i or 720p capable TV, do Blu-Ray players down-convert to 720? Or is it just not viewable unless you have a 1080-capable TV?

Thanks!

Originally Posted by yoda313

I have a 720p tv (1366x768 native res) and a ps3. I have it connected via hdmi. The ps3 will support up to 1080p - depending on the source of course - such as a bluray 1080p disc - but only outputs up to your max on your set. I have all video resolutions ticked for output on the ps3. I get 1080i on the tv.

I'm confused. You say that your ps3 supports up to 1080p, but only outputs to the max of your TV (720p). But then you say you get 1080i on the TV. Those sentences seem to contradict one another. Am I missing something?

I may be wrong but I think the 720P LCD will downconvert the 1080 i/P upconverted signal to it's native 1366 x 768.

With very few exceptions Blu-ray discs are 1080p,HD tv broadcasts are 720p or 1080i.
Your tv will scale the source to it's native resolution.

Originally Posted by edDV

But home made Blu-Ray discs can have a wide choice of supported resolutions. The player will rescale all of these to the user chosen output resolution.

True but I was referring to store bought pressed Blu-ray discs.It's best to set the player to the highest resolution your tv can handle and let the tv scale.

OK, thanks @ all. I am understanding that either the Blu-ray player and/or HDTV will up or down-convert according to the option selected by the user. That seems to create a lot of flexibility in viewing options, which is good, because it provides for maximum compatibility regardless of what player/TV a person has. It does make me wonder though... just how good does the hardware up or down convert?

Earlier it was mentioned that a 720p LCD had a native resolution of 1366x768. I thought the '720' meant 720 pixels, so that the native resolution was 1280x720?

Having said that, what then is a 1080i or 1080p HDTV's native resolution? Is it 1920x1080? Or something different?

What I am ultimately driving at is this -- I want to author a Blu-Ray disc when I get a BDR burner in a couple of months and I want to author it in the highest possible resolution. But I'm ready to start the production process now and I want to render the video/animation files so that I don't have to rescale it when I author it because I don't want to introduce any degradation in the rescaling process. Also, if the viewer has to rescale (because they don't have top of the line equipment), then I prefer that their hardware downscale it rather than upscale it since downsizing usually degrades less than upsizing, right?

So, for optimal results (i.e., 1080p) should I render at 1920x1080 and then encode progressive? My source files are interlaced since they are rendered on a PC.

Well, the beauty of it is that since I am rendering the source animation, I can make it any size I want. I am just trying to determine what the best resolution should be to produce the highest quality HD viewing once it is burned onto BDR. In that effort to maintain quality throughout the process, I am trying to avoid having to rescale during the encoding or authoring process. I want those steps to just encode and convert to BDR format, not have to rescale too.

I can tell you that since the files are rendered on the computer, the resulting animation is being saved as an uncompressed .AVI that is interlaced. It creates some HUGE file sizes, but I have a 4TB RAID so space isn't a problem. I'll compress the file when I get to the encoding step.

So, in your opinion, does 1920x1080 encoded progressively produce the best result or should I use a different approach?

OK, thanks so much edDV. Your subject matter expertise really helps. This project will be for HDTV only, so it looks like 1920x1080p @24p is the way to go.

Regarding the 24 fps, most of my animation is fast moving so I am concerned that rendering 24fps may cause the motion to be a little choppy instead. I was planning on rendering 29.97fps or higher to make movement smooth. However, since my source animation is interlaced and there is nothing I can do to change it, should I encode interlaced or encode progressive?

According to the Blu-ray spec, there are two 1920x1080 options:

1920x1080x59.94i, 50i (16:9)
1920x1080x24p, 23.976p (16:9)

How much better is progressive than interlaced anyways? Just trying to weigh the trade-offs. It definitely is a lot less frames (not to mention storage space and time), which is attractive, but do you have any idea if there will be any undesirable effects from progressively encoding an interlaced source?

I tried a little test and encoded a small 1920x1080x29.97fps interlaced clip to 1920x1080x24fps progressive. Based on this little clip, I couldn't see any noticeable improvements, but it did get choppy because it had to drop 6fps.

I'm going to re-render that same small clip at 1920x1080x24fps, then encode to 1920x1080x24fps to see the results, mainly if the motion is choppy or acceptably smooth. I like the idea of progressive scan, fewer frames, and ability to convert to Euro-PAL, if necessary. I just need to see if I can get away with a slower frame rate. I'll let it crunch overnight and post the results in the morning.

Worst case, if 24fps is too slow, then it sounds like I could still render at 1920x1080x29.97fps interlaced and encode at 1920x1080x29.97fps interlaced, correct? Or would I have to render and/or encode at 59.94fps to be compliant with the spec if I go the interlaced route?

Well, the good news is the 're-render at 24fps' test turned out pretty good. The motion was not as smooth compared to at 29.97fps, but the difference is hardly noticeable.

So, all things considered and thanks to your expertise, I think the best way to go is for me to render the animation at 1920x1080x24fps interlaced and then encode 1920x1080x24fps progressive. This will be 20% fewer frames to render, saving a lot of time and storage space.

Since I plan to make the BDR in NTSC format, I'm still not clear on the impact to European PAL viewers. When you say:

Originally Posted by edDV

For Euro-PAL, the frames would be played 4% fast to 25 fps and sound would be processed.

A PAL Blu-Ray player will play 1920x1080p/24 directly and make the conversion to 25 fps.

Are you suggesting that Europeans may be able to play a NTSC BDR on their PAL Blu-Ray player which will make the conversion to 25fps, resulting in a 4% increase in video and sound speed? I was under the impression that the disc needed to be in PAL format for them to view, which would necessitate releasing two BDRs (one NTSC version and one PAL version). But it would be cool if I could get away with just one (NTSC) version if the only impact to European viewers would be a 4% increase in play speed. That seems to be a minimal increase... not so massive that vocals would sound like Alvin & The Chipmunks.

OK, will do, thanks!

Originally Posted by blazin-j

I tried a little test and encoded a small 1920x1080x29.97fps interlaced clip to 1920x1080x24fps progressive. Based on this little clip, I couldn't see any noticeable improvements, but it did get choppy because it had to drop 6fps.

There is a big difference between 24 fps progressive and 30 fps interlaced (60 different half-pictures per second) especially without motion blur. Make yourself a medium speed smooth panning scene and it will be very obvious. If the two fields that make up a frame are from the same point in time (not interlaced) the difference isn't as big.

Watch this 60 fps AVI file on a 60 Hz monitor, full screen:

24v30v60.avi

The top line is 24 fps (frame repeated 2x, 3x, 2x, 3x... to make 60 fps), the middle line 30 fps (frames repeated twice each to make 60 fps), and the bottom line 60 fps (every frame unique). This is what your TV does when displaying the different source frame rates. The tradeoff with 30i is you get less vertical resolution (per field) and more jagged color edges because of the interlaced encoding. Depending on your animation software, it may take much longer to render. And PAL conversion would be best done by rerendering at 25i, rather than trying to convert from 30i.

That's a cool demo! Thanks for sharing that. In viewing it, I really didn't like the top or the middle line, lol. The way I saw it, if I were forced to choose the better of the top two lines, I'd probably choose the top line because the middle one seemed to wobble more noticeably on the horizontal plane. But, frankly, I'd really like to obtain results like the third line. So how would I achieve that?

Back to the Blu-ray spec, there are two 1920x1080 options:

1920x1080x59.94i, 50i (16:9)
1920x1080x24p, 23.976p (16:9)

I'm not clear whether I should be shooting for the first option by rendering and encoding 59.94 fps interlaced or the second option by rendering and encoding at 23.976 fps progressive...

Can you provide some guidance Jagabo?

Each frame of interlaced video contains two half-pictures, each to be displayed alone and sequentially. If you want this very smooth motion you want to create 29.97 fps 1080i -- the player or TV will convert this to 59.94 fps on-screen. But make sure your rendering program produces the requisite 59.94 different half-pictures per second, not 29.94 full pictures and simply calls it interlaced. If the rendering program doesn't have an interlace option you have to render 59.94 progressive fps then produce 29.97i yourself. I would use AviSynth with SeparateFields().SelectEvery(4,0,3). You might want to render 59.94 progressive fps anyway -- it will be much easier and cleaner to produce 720p60 from 1080p60 than from 1080i.

And keep in mind, the jerkiness is much less noticeable with more "normal" video. That particular example was designed specifically to display the differences and is about a worst case example. You probably watch 24p movies all the time and don't really notice how jerky it can be.

Wow, your post made me revisit an assumption that I had made -- that the uncompressed .AVI file was interlaced. I went back and checked, only to find out that the .AVI file is NOT interlaced, but rather a bunch of still images it plays in sequence at the specified frame rate.

So, does the fact that the source file is non-interlaced mean that it is progressive?

At this point, the 30fps render looks slightly better (less jerky) than the 24fps. I'm just wondering if I should render at even a higher fps rate given that I can choose to encode interlaced or progressive at this point.

Should I attempt rendering at 59.94 fps and encode progressively? Or would I be forced to encode interlaced at that frame rate?

My understanding is the Blu-Ray spec allows for two 1920x1080 options:

1920x1080x59.94i, 50i (16:9)
1920x1080x24p, 23.976p (16:9)

OK, I think I'll put my PC back to work to render some sample clips at 1280x720p/59.94 and compare the results against the 1920x1080i/29.97 clips I have to see what offers the best results.

Thanks for all your help!

Originally Posted by blazin-j

OK, I think I'll put my PC back to work to render some sample clips at 1280x720p/59.94 and compare the results against the 1920x1080i/29.97 clips I have to see what offers the best results.

How are you going to watch them? On a computer the player will make a difference. It has to bob 1080i to get 59.94 fps playback.

Yes, the AVI sample I provided was 60p because it takes the correct setup to play 30i Xvid AVI in Windows. Here's a quick 29.97i TFF MPEG 2 M2V you can author to DVD:

24v30v60.m2v

And an ISO image ready to burn:

24v30v60.zip

Originally Posted by jagabo

How are you going to watch them? On a computer the player will make a difference. It has to bob 1080i to get 59.94 fps playback.

Well, that takes the wind out of my sails because, yes, I was watching the sample clips I've made on my PC's monitor. So, I guess this means I'll have to make the plunge in buying the Blu-Ray burner for my PC and Blu-Ray player for my HDTV sooner than expected because it seems I won't truly be able to get a good idea of what settings will be optimal until I view it on that equipment...

Originally Posted by edDV

The equivalent for "PAL" would be 1280x720p @50 frames per second.

Am I correct to interpret this to mean that if I encode a 1280x720p/59.94fps, then European PAL players will play it but at about a 16% slower rate? If so, that's a big differential and probably wouldn't be feasible. It will most likely necessitate a separate PAL version encoded at 1280x720p/50fps, right?

This is all getting a little complicated, LOL!

Originally Posted by blazin-j

Originally Posted by jagabo

How are you going to watch them? On a computer the player will make a difference. It has to bob 1080i to get 59.94 fps playback.

Well, that takes the wind out of my sails because, yes, I was watching the sample clips I've made on my PC's monitor.

You can view it bob'd on a computer monitor. You just have to use the right player. Try using MPCHC or VLC. For the purpose of viewing motion smoothness you render at 720x480 and use DVDs. The frame/field rate issues are the same.

Originally Posted by blazin-j

Originally Posted by edDV

The equivalent for "PAL" would be 1280x720p @50 frames per second.

Am I correct to interpret this to mean that if I encode a 1280x720p/59.94fps, then European PAL players will play it but at about a 16% slower rate?

No, they will throw away 1 frame out of every 6 to reduce the frame rate to 50 fps. Running time will be the same but there will 10 little jerks every second.