How to detect pillarboxing in AVISynth

[GoneToTheDogs]

Is there any way using AVISynth to detect whether an HD video stream is really pillarboxed 4:3 content?

I have an MPEG-2 transport stream that I am trying to split up using the Haali splitter, decode, and re-encode, but sometimes the content is really just pillarbox'd 4:3 content, and I need a way to programmatically determine whether it should be cropped.

Is there any way to do this with AVISynth?

Many thanks,
jack

(p.s. - my apologies if this happens to be a dupe, I searched in the forums and couldn't find what i was looking for)

[manono]

Hi-

I need a way to programmatically determine whether it should be cropped.

The AutoCrop filter?

http://avisynth.org/warpenterprises/

From the accompanying text file:

AutoCrop is an AVISynth filter that automatically crops the black borders from a clip.

Perhaps not what you had in mind, though.

[gadgetguy]

I could be wrong, but I don't think so. All of the filters that I have used require manually setting the options and viewing the results to see if they are correct. You can easily remove pillarbox in AviSynth, but I don't think there's a way to automate the process if it's not told it's pillarboxed content.

Edit: Just read manono's reply. Never heard of it, but if it works...

[manono]

Yeah, gadgetguy, the Autocrop crops all black. That's why I'm not sure that's what GoneToTheDogs is looking for. I think he's looking for some automatic solution that detects only pillarbars and crops them, so the video can be reencoded as 4:3.

[guns1inger]

However, if the clip is 4:3 delivered in a 16:9 stream, not only does it have to be cropped, but it also has to be resized back to 4:3 resolution. Not sure that it is worth the effort, or image degradation, personally.

[manono]

Maybe I'm jumping to conclusions without any evidence, but I assumed he's reencoding for DVD, or maybe something else he wants in a lower resolution (AVI?). If so, he'll be resizing anyway. If not, then I agree there's no point to the exercise.

Of course, he could just look at it and tell if it's from a 4:3 source.

[gadgetguy]

Starting from an HD stream the degradation might be acceptable if going to another format like DVD.
I just looked at the autocrop feature and read the txt file. It might work, although the creator doesn't seem to have much confidence in it.
From the txt file:

I strongly suggest using the preview mode before committing to a particular crop.

But it also assumes the pillar box is encoded into the stream. I don't have any experience with HD transport streams, but is that normal? or are there A/R flags like for DVD content and the pillar boxes are added by the player?

[guns1inger]

I know that Australian digital broadcasts are all 16:9, so 4:3 material is pillarboxed. Most digital players have a 4:3 (or fullscreen) mode that zooms for you (and does a much better job than any DVD player I have seen), but if you cap the stream you get the full 16:9, pillarboxed image.

[GoneToTheDogs]

I am in fact re-encoding (and will adjust the aspect ratio to 4:3), and a small loss of quality is acceptable -- if that autocrop filter can automatically detect and crop the black pillars then it is truly a god-sent!!! Thank you all for your help, I'll give that filter a try and post back with my results.

[GoneToTheDogs]

AutoCrop did the trick, thanks so much! I am very grateful for your kindness and expertise!