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Extreme aliasing - Apple DVD player viewing SD down convert.

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Denis Devlin
Extreme aliasing - Apple DVD player viewing SD down convert.
on Dec 29, 2009 at 5:42:48 am

Video taken with Sony EX1 at 720-p60 was down converted using Compressor 3.0.5 (best compression, best frame controls) to SD and then muxed to NTSC DVD using DVD Studio Pro 4.2.1. The resulting DVD was displayed using Apple's DVD player application (version 5.0.3 on leopard) as shown below:

The extreme aliasing artifact seen on the cello bow in the frame grab exhibits itself as a ridiculous twittering candy stripe when seen in motion. Not all frames show the problem, but many do including runs of a dozen or so adjacent frames.

I had concluded that something had gone terribly wrong with the HD to SD conversion - so I did the conversion again using other settings etc to achieve varying results, all unacceptable. (E.g. compression with a GOP of 6 or 7 frames, various IBP patterns, various frame control settings).

But then I displayed the DVD using VLC instead of Apple's DVD player. What a difference ! !

This second frame grab is taken of exactly the same frame from the exact same DVD/VIDEO_TS folder. I am not comparing different encodings here - the only difference is the player application that is decoding the muxed mpeg-2 and displaying it on the computer screen. There are no settings being tweeked in either player.

What is going on here? I never heard anyone say that the software (or hardware?) used to view a dvd could be such an important variable. Now I have to discard any conclusions reached when comparing various down convert strategies and ask myself what different conclusions I might have come to when viewed through a different player. I suppose I could hope that the VLC player always does a better job of rendering the mpeg-2, but I hesitate to reach such a general conclusion for an issue that seems so mysteriously complicated.

Is Apple really just shipping a lousy decoder? - or is there some type of footage where the roles are reversed and VLC player will show problems that the Apple player hides? I have seen some postings from many years ago complaining about the quality of Apple's DVD player - but I am seeing this on the latest Apple DVD player for OS 10.5.8. Any insights will be appreciated.




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Zane Barker
Re: Extreme aliasing - Apple DVD player viewing SD down convert.
on Dec 29, 2009 at 7:16:05 am

A computer screen is NOT the place to judge the quality of a DVD. DVDs are built to play on TVs so that would be the better place.

Each app may handle interlacing differently and from looking at the two screen shots that seems to be the issue.

Oh and FYI this question your post really has noting to do with FCP so this forum is not really the best place for it.



There are no "technical solutions" to your "artistic problems".
Don't let technology get in the way of your creativity!



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david bogie
Re: Extreme aliasing - Apple DVD player viewing SD down convert.
on Dec 29, 2009 at 3:25:10 pm

Your frame grabs are not aliasing issues; it appears to be how the player is set to process and display interlacing.
Anti-aliasing is part of the encoding or rendering process, not playback.

You could drop the nice folks at VLC a line and ask them why their image is so superior and you could research the Apple DVD Player application at apple.com's discussions area.

There are some viewing options for both applications that may be different. See the VIEW menu for DVD Player for interlacing display options and size options.

I do not have VLC on my office machine to check it for you.

bogiesan



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Denis Devlin
Re: Extreme aliasing - Apple DVD player viewing SD down convert.
on Dec 29, 2009 at 4:11:32 pm

The original footage is not interlaced - it comes from Sony Ex1, 720p60. Compressor is setup to produce a progressive mpeg encoding - not interlaced.

There are no relevant options that I can find in either the Apple DVD player or in VLC. Both are using defaults and there is nothing much that can be changed. The display size in both cases is "actual size" (I posted just a portion of the actual size screen image).

I suppose a DVD player is the best way to decode mpeg-2 content and then view it on a tv screen, but having seen the extreme difference in these images, do we also need to test on various DVD players to see which decodes well versus poorly? And in this day and age, many people do actually play dvds on their computer. Is the conclusion as simple as: "use VLC instead of the Apple player in order to avoid extreme artifacts in some cases" ?

Although this comparison of DVD player versus VLC is not directly relevant to FinalCut , it does seem valuable to point out that the final quality of a video image does seem to depend in some cases dramatically on the player used to view it. And perhaps there are specific encoding parameters that would avoid the problem illustrated by the frame grabs. That is my reason for posting here - maybe others have run into similar problems and figured out a work around. I am also interested to know if anyone has examples where the Apple player works well but VLC makes a mess out of the image.


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Dave LaRonde
Re: Extreme aliasing - Apple DVD player viewing SD down convert.
on Dec 29, 2009 at 6:26:03 pm

[Denis Devlin] "The original footage is not interlaced - it comes from Sony Ex1, 720p60. Compressor is setup to produce a progressive mpeg encoding - not interlaced. "

That doesn't matter: the footage is still interlaced. That's because the NTSC technical standard for standard-definition video calls for two interlaced fields. Even on progressive scan stuff.

Look at your stuff on a TV set and not on a computer monitor and life gets better.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Denis Devlin
Re: Extreme aliasing - Apple DVD player viewing SD down convert.
on Dec 29, 2009 at 7:01:22 pm

I suspect (hope !) that the footage will look ok on a tv, just like it looks ok using VLC. But, I am not convinced the issue has anything to do with interlacing and it still seems inexcusable that the Apple DVD player behaves so badly.

Here is some Apple documentation for Compressor:

*******
About Standard Definition MPEG-2
Standard MPEG-2 is full frame rate (23.98–29.97 fps) and full-screen resolution (720 x 480 for NTSC and 720 x 576 for PAL). MPEG-2 has the following characteristics.

Support for interlaced video: MPEG-2 can support either interlaced or progressive video.

HD to SD Downconversion
For those situations in which you are editing high definition (HD) sources in Final Cut Pro and want to create a standard definition (SD) DVD from them, Compressor provides high-quality downconversion. Compressor retains as much detail as possible during scaling and correctly preserves progressive or interlaced formats when encoding to MPEG-2 for DVD.
*************

I believe that DVD players that are rated to support "progressive scan" will properly interpret the "progressive format" which is output by Apple's compressor. Presumably, Apple's DVD player application also knows how to correctly interpret and play the progressive format mpeg. Perhaps in my example, something has gone wrong with the encoding so it is not correctly output as progressive - but then why does VLC not stumble in the same way?


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Dave LaRonde
Re: Extreme aliasing - Apple DVD player viewing SD down convert.
on Dec 29, 2009 at 7:33:15 pm

[Denis Devlin] "I am not convinced the issue has anything to do with interlacing and it still seems inexcusable that the Apple DVD player behaves so badly. "

Well, it DOES have something to do with interlacing -- you're only seeing half of the vertical resolution in the shot in the Apple DVD Player, because you're only seeing one field. And if you're taking it as an article of faith that the Apple DVD player works flawlessly, I'm here to tell you that it ain't so hot, as witnessed by your own eyes.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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