WHY can I not get a truly raw render?

[Vince Becquiot]

I Marc,

You know I have to ask to be sure, any de-interlacing going on?

How are you comparing those 2 outputs? I don’t mind doing some testing on my end.

CS4 should actually give you a cleaner output since it actually uses more precise PAR than in previous versions.

Vince Becquiot

Kaptis Studios
San Francisco – Bay Area

[Marc Brown]

Thanks for replying.

No deinterlacing per se. There are two source materials in the same timeline and the degradation affects both:

1: A mpeg2 video (from DVD) at 23.976 progressive fps.
2: A raw 23.976 progressive fps render from AE which was itself originally a 29.97fps mpeg2 video from DVD which I painstakingly reconstructed in AE with reverse pulldown.

To compare footage (before and after Premiere Pro sends it through Media Encoder, whether for “raw” or mpeg2 encoding), I consult Premiere Pro’s preview window, zoomed in to 400% so I can discern finer detail. The kind of degradation which occurs certainly doesn’t require close inspection to be recognized.

I had considered for a moment that perhaps what I was seeing was a loss of chroma resolution, due, at least in the case of mpeg2, to the nature of the video format. But this wouldn’t make sense, because all of the source video WAS originally mpeg2, so any loss of chroma resolution would already have been inherent. And besides, that would do nothing to explain why the supposedly raw renders undergo the same degradation.

[Jon Barrie]

Hi Marc,
one of the most commonly Mis-understood aspects of compression has to do with recompresion.
if a video starts from DVD mepg2 and is then edited, it must be recompressed upon export as the group of pictures properties (GOP) has been altered in the process of editing. The chance that the GOP will line up with the export GOP settings is near impossible.
This kind of compressing something compressed, (generation) will result in poorer quality exports.
Converting the mpeg2 to uncompressed before exporting to mpeg2 again won’t make it any better at the export stage.
I hope this clarifies your results.
Respectfuly,
Jon Barrie 😉

Jon Barrie
aJBprods
http://www.jonbarrie.net
http://www.suiteskills.com

[Marc Brown]

Thanks for the information. In this case, the considerations you point out were not completely misunderstood by me.

I point out that the degradation I am seeing is happening here:

Input: raw video (exported from AE as raw)
Output: raw video (exported from Premiere Pro through Media Encoder as raw)

No compression is inherent in the raw source. Hypothetically, no compression should be taking place in the raw export. The degradation I am seeing is NOT visible on the input file (raw from AE, remember) prior to export. Also I need to be specific in saying that the input file is not an AE project file but an actual raw render.

[Jon Barrie]

Hi Eric, can you verify the term RAW. It’s not used in video. Uncompressed is commonly used but I’m not sure that what you mean. RAW is a format used in photography terms for uncompressed photos.
A raw 23.976 progressive fps render from AE which was itself originally a 29.97fps mpeg2 video from DVD which I painstakingly reconstructed in AE with reverse pulldown.
Did you rebuild an AE project based on an mpeg video as your reference? Or did you convert the mpeg video itself from 29.97 to 23.976?
What resolutions are your AE comps, clips and ppro sequences?
Cheers,
Jon Barrie 🙂

Jon Barrie
aJBprods
http://www.jonbarrie.net
http://www.suiteskills.com

[Marc Brown]

> can you verify the term RAW

My bad. “Raw” is my shorthand for “uncompressed.”

> Did you rebuild an AE project based on an mpeg video as your reference? Or did you convert the mpeg video itself from 29.97 to 23.976?

Within AE, I imported the original 29.97fps mpeg2 video, did my edits (this involved performing reverse pulldown on different segments of the video, as the phase kept changing from scene to scene), and allowed AE to output the result as an uncompressed video some 130GB in size. 8 bpc, I do believe.

> What resolutions are your AE comps, clips and ppro sequences?

AE comp is 704×480 NTSC non-widescreen 23.976fps, as is its raw output which I use in PPro. The other source – an mpeg2 video – is 720×480 NTSC widescreen 23.976fps. The PPro sequence is its preset for DV NTSC widescreen 24fps.

In spite of the variability between the two source videos (widescreen vs. not, and differing resolutions), I again stress that no degradation of either video is apparent in PPro’s video preview prior to the uncompressed render, yet BOTH sources get degraded in the same manner upon rendering.

[Jon Barrie]

Ok, so then the recompression situation is actually happening here.

the AE rendered file is not actually uncompressed data, it is an uncompressed version of the original mpeg2 compression.

In order for you to have clean export with progressive material you need to be in a progressive sequence in PPro.

If the DV preset used is interlaced then you export the sequence as progressive it will deinterlace it = loss of half the resolution. Then there is the render with preview files. If this is ticked then you will be using the DV compressed renders to then compress to whatever your export settings are going to.

If you are rendering out to Quicktime with the codec set to Animation 100% you will end up with a large file but not real gain in video quality. MPEG2 export from this will incur a quality hit, that is just mathematics of compression, and recompression. MPEG compressed to MPEG (generation) will always incur in loss of quality.

Can you upload a couple of still frame screen grabs for out comparison. If it is as simple as making a new seq in desktop mode, which i feel it will need to be, then copying and pasting the edit into it you should be home free.

Let us see the results it will help us to pin point the actual problem. 🙂

– Jon Barrie

Jon Barrie
aJBprods
http://www.jonbarrie.net
http://www.suiteskills.com

[Marc Brown]

Thanks for your help. I should have clarified that the PPro preset I used was 24fps (progressive).

I’ll be happy to (attempt to) post a couple of screen grabs once I return home and have the project in front of me. I hope this won’t prove too late in the day.

[Marc Brown]

I rendered off four .BMP frames from my project:

1: From the mpeg2 source, before rendering as uncompressed
2: From the mpeg2 source, after rendering as uncompressed (reimported to Premiere Pro)
3: From the (mpeg2 29.97fps -> AE 23.976 uncompressed) source, before rendering as uncompressed
4: From the (mpeg2 29.97fps -> AE 23.976 uncompressed) source, after rendering as uncompressed (reimported to Premiere Pro)

On a wild guess, I decided to take these four frames and see how they looked in the rather more predictable (and preferred) After Effects. To my mild surprise, the phenomenon of horizontal resolution degradation was not apparent. However, there were still some subtle chroma & luma differences, underscoring the remaining fact that I still haven’t gotten a truly uncompressed (and I mean identical) WYSIWYG render from PPro.

This begs the question: What is PPro’s inherent flaw which causes it to misrepresent a frame of video in such catastrophic fashion? You give it an uncompressed or mpeg2 video from another source such as AE, and its Program Monitor window displays the frame correctly, but you give it video rendered with Media Encoder (mpeg2 OR uncompressed) and it somehow crushes the horizontal resolution _in the Program Monitor window_ but not in fact?

[Jon Barrie]

Please post your results by uploading to the cow reply post interface.

Jon Barrie
aJBprods
http://www.jonbarrie.net
http://www.suiteskills.com