Resolutions, AR and cropping

[tominator]

Hello
I've been trying to find good info on this for a while. Ive found a whole lot at doom9.org but not enough.

I'm using Canopus ProCoder 2.0 to make WMV-streams from DVD-sources.

I start by demuxing the DVD to a m2v- and an ac3-file and this is where the problem starts. More often than not I end up with a video file with black bars on either left and right, top and bottom or even on all four.

Ive tried the cropping filter in ProCoder but it messes with my AR. I want the same AR as the original movie but I can't see how I would do this without wither leaving a bit of the black bars or cutting from the actual picture. I have to cut as much from left and right as top and bottom, right?

Also, could someone explain what the numbers on the covers mean? 1.85:1, 2.35:1 and so on.

This is a big problem for me so if Ive missed some important info in this post please tell me and Ill add it in an instant.

Thanks.

[jggimi]

Hello, and welcome to the forum.

Lets start with film: The directors and cinematographers have a great many aspect ratios to choose from, and sometimes they choose multiple ARs for the same film -- they might use a slightly different AR on prints used in theatrical release, or they might have multiple theatrical releases with different ARs. Just as one example (picked from memory), Stanley Kubrick's Full Metal Jacket had two different theatrical ARs: 1.66:1 in European release, and 1.85:1 in North America. Those numbers, since you ask about them, are the ratio of width:height. If you look up technical specs, you will also sometimes see ARs for the negatives (or film prints, which are the same). In the example I just used for FMJ, the film AR is 1:37:1. That's because they used anamorphic lenses when filming and when projecting, which changed the image shape.

Once a film has been transferred to DVD:

Full size commercial DVDs are always a fixed resolution -- 720x480 NTSC or 720x576 PAL. And, they always have a fixed AR: 4:3 or 16:9, to match the shape of televisions. 4:3 (1.33:1) are "standard" television shapes, and 16:9 (1.78:1) are "newfangled." Because DVDs have a fixed resolution, they have a flag that tells your DVD player which aspect ratio the video stream is using. And your DVD player, if you set it up when you got it, knows the shape of your TV.

Because there are only 2 ARs with DVDs, but a veritable smorgasbord of film ARs, a transfer from film to DVD that doesn't match 1.33:1 or 1.78:1 must use letterboxing or pillarboxing in order to recreate the appropriate aspect ratio on playback.

Those of us who backup DVD to other formats typically crop away that letterboxing/pillarboxing, and those of us who intend the video to go into AVI or other containers where square pixels are expected ... resize.

Note that modern video codecs compress with colorspaces that convey color information for multiple pixels -- these technologies limit resizing options and one may get small amounts of aspect ratio error, which are usually unnoticeable.

You can look up the technical specifications (as provided by the production companies) at www.imdb.com and get lots of interesting information about your various films. Those numbers you see on the covers of DVDs are the film's aspect ratio when transferred to digital media, which might differ from theatrical prints ... or be completely erroneous (as can imdb.com's too, I suppose).

----

16:9 DVDs are sometimes called "anamorphic" -- because they get resized by DVD players when played back on standard TVs. When playing back on square-pixel PC monitors, both 4:3 and 16:9 DVD video streams have to be resized. DVDs do not have square pixels. So for PC playback, both are really "anamorphic" -- though the term more appropriately applies to lenses and camera/projection systems for film. I'm going to guess that this is where your AR problem lies -- DVD content must be resized for playback on PCs, as they have square pixels, and DVDs do not.

Edited for clarity and spelling.

[quake74]

:goodpost: IMHO jggimi post should go straight into the newbie's FAQ!

[tominator]

Thank you. Your post was very helpful and informative.

But I didn't feel like I got an answer to my most most important question as to how to crop the black bars away and still have the same AR.

If I crop with a fixed container to have the same AR I wont get the whole picture in my output whereas if I crop the whole picture I will get strange AR.

For 1.78:1 I use 640x352 and for 1.85:1 I use 640x360.

Thanks again.