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Need some help understanding interlacing maybe?

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Michael Mackus
Need some help understanding interlacing maybe?
on Mar 1, 2010 at 1:29:40 am

Hello all,

First off please excuse my lack of information. I recently got into digital camcording, and have a simple Sony DCR-DVD610 which outputs in MPEG-2 to the memory card an am shooting in the 4:3 AR. I have Adobe After Effects CS4 and Sony Vegas 9.

Let me give a scenario I'm sure you have heard many times and you can point me in the right direction because I am a wee bit lost.

When I view the raw .mpg on my computer it is of course interlaced, and everything seems in proper aspect ratio. When I view a recorded plate.. it is round.

Now I create a new comp in AE, which is defaulted to 720x480. I import this vid of the plate. My plate vid now seems stretched, I can already see this, the plate is no longer round. I go ahead and do what I want with new layers and when it comes time to add to the render queue and render.. I choose the default, "Video for Windows" (.avi) lossless and render.

The resulting vid is the same as I saw in After Effects, out of aspect and the plate is now fatter wide than tall and no longer round.

If I either stretch to 720x534 or to 640x480 the resulting output .avi is in correct aspect but I see loss.

What am I doing wrong? This is a standard SD cam with both 16:9 and 4:3 and I dont understand why After Effects always destroys the aspect in its default setting. Can someone please help this noob understand?

I'm not sure what the best way to output my videos to send to friends on the net etc.

Please help! Thanks so much,


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Michael Szalapski
Re: Need some help understanding aspect ratios
on Mar 1, 2010 at 2:29:05 pm

Just out of curiosity, what are you using AE for? Unless you're doing some swooshy motion graphics or compositing, there's really no need to step out of your editing program.

But, on to your issues.

For one thing, you don't want to use the straight MPG files from your camera in After Effects. AE is not a video editing program. It handles video very differently from Premiere, Final Cut, Vegas, etc. and AE doesn't play well with MPG video. Dave LaRonde explains why:
Dave's Stock Answer #1:

If the footage you imported into AE is any kind of the following -- footage in an HDV acquisition codec, MPEG1, MPEG2, mp4, m2t, H.261 or H.264 -- you need to convert it to a different codec.

These kinds of footage use temporal, or interframe compression. They have keyframes at regular intervals, containing complete frame information. However, the frames in between do NOT have complete information. Interframe codecs toss out duplicated information.

In order to maintain peak rendering efficiency, AE needs complete information for each and every frame. But because these kinds of footage contain only partial information, AE freaks out, resulting in a wide variety of problems.
And Adobe agrees.

So Render out of Vegas something you want to work with in After Effects. I'm not sure what options Vegas has, I've never worked with it.

Now, as to your aspect ratio problem: After Effects is not "destroying" your video. You are. :) It's only doing what it's told to do.
You need to tell After Effects how to interpret your footage. I would suggest you import your footage and then just drag it onto the new composition button. It will then create a composition to match the footage. There is an aspect ratio correction button at the bottom of your comp window. You may need to push this button to get it to display "correctly". Then, when you output your video with the Render Queue, you will need to make sure the video you're outputting is the correct aspect ratio as well.
You can read about interpreting footage here and you can read about rendering here.

Also, since you're wanting to put out videos for your friends to see, I shall point your attention to another Dave LaRonde thing that will be useful for you:
Dave's Stock Answer #3:

Don't use AE to compress files for final delivery. The various compressors are there...etc. AE is incapable of doing multipass encoding, a crucial feature that greatly improves the image quality of H.264 and MPEG-type files in particular.

Render a high-quality file from AE, and use a different application to do the compression. Popular ones are Adobe Media Encoder, Sorenson Squeeze and Apple's Compressor, which comes bundled with Final Cut Suite. Even compressing in Quicktime Pro is better than compressing in AE.

Making good-looking compressed files is almost as much an art as it is a science. It is NOT straightforward at all. I recommend asking a few questions at the COW's Compression Techniques forum.

This is a professional program, intended to be used by people with exprience in the industry, so it can take a while to get used to all this stuff.

- The Great Szalam
(The 'Great' stands for 'Not So Great, in fact, Extremely Humble')

No trees were harmed in the creation of this message, but several thousand electrons were mildly inconvenienced.

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Michael Mackus
Re: Need some help understanding aspect ratios
on Mar 1, 2010 at 10:20:58 pm

Wow. Thank you Michael for a very comprehensive and well explained reply. I have researched PAR and although I feel a bit foolish, I do understand it now.

Your tips regarding most notably.. importing into AE (as well as not compressing out) are invaluable. Thank you so much. :)


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John Cuevas
Re: Need some help understanding interlacing maybe?
on Mar 1, 2010 at 2:36:46 pm

To the aspect ratio question, AE displays in square pixels, so when you bring in your video it will show you a square pixel display of a non-square pixel source. Your video may looked squished in AE, but it's probably not.

Under the display window, there is a toggle aspect ratio button. This will approximate 4x3 and 16x9 on a computer(square pixel monitor).

Most importantly you need to make sure your composition is setup correctly. The easiest way to do this would be by just taking your footage and dropping it on the make new comp button in the project panel.

Unless I miss my guess, you have 4x3 footage, but you have made a 16x9 composition. If you hit cntl-k on your already made composition, change the Pixel Aspect Ratio to .9 instead of 1.2. It maybe happening because AE is incorrectly interpreting your footage---right click on the footage in the project panel to make sure it's being interpreted as 4x3

As for compression-there are so many ways to send things. Flash, WMV...for our client previews, generally a 50% size wmv works pretty good.

Johnny Cuevas, Editor

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Michael Mackus
Re: Need some help understanding interlacing maybe?
on Mar 1, 2010 at 10:27:55 pm

Thank you for your response as well John. I now better understand PAR, something I previously knew nothing about (yes i know I have a long way to go lol). It is nice to see the knowledgable help others.


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