Cropping with VirtualDub

[Steve Riley]

I've installed VirtualDub-MPEG2. I open a VOB I ripped. I want to crop the black bars. When I do this using the null transform filter, it also changes the width in the output window.

It's a 16:9 movie, and I'm guessing the pixels in the VOB aren't square. No matter what I do, VirtualDub seems to convert to square pixels whenever I tell any of the filters to crop. How can I configure VirtualDub just to crop the black bars without adjusting the size of the output?

[KBeee]

You could try -
VirtualDubMPG2/Options/Preferences/MPEG, and tick the box called
"Automatically adjust preview window to display MPEG aspect ratio"

[jagabo]

Pixels in VOB files are not square, both 4:3 or 16:9 sources. All versions of VirtualDub display video with square pixels by default. This allows each pixel in the video to be mapped to one pixel in the display -- so you see each and every pixel of the frame, not a processed, aspect ratio corrected image.

If you want to convert a video to square pixels (with the correct overall picture aspect ratio) you have to use the Resize filter. For example, if you want to convert a 720x480 4:3 VOB you could resize to 640x480. A 16:9 VOB could be resized to ~720x400 or ~640x360. A 2.35:1 AR movie could be resized to 640x272 after cropping away the black bars.

[Steve Riley]

Thanks, jagabo. But if I don't know ahead of time what the aspect ratio of the movie is, how can I calculate the correct resize?

[Alex_ander]

If your original 16:9 MPEG movie was properly bordered, you don't need to measure or calculate its AR (e.g. was it 1.85:1 or 2.35:1). You can resize it with its original borders to pixel ratio 16:9, then crop the borders (use even numbers). This will give an avi with original image proportions.

[jagabo]

There are only two aspect ratios used on DVD: 4:3 and 16:9. Any other aspect ratio has black borders added to the picture to fill up the 720x480 frame.

If your DVD is 4:3 resize to a 4:3 frame size then crop the top and bottom black borders. For example, resize to 640x480 then crop the borders.

If your DVD is 16:9 resize to a 16:9 frame size then crop the top and bottom black borders. For example, resize to 640x360 and crop, or resize to 720x404 and crop.

Note that most codecs have restrictions on the frame size, most require at least multiples of 2 or 4. And most work best with multiples of 16. Solid black borders compress very well so leaving a little doesn't cost you much.

[Steve Riley]

Finally got this figured out after reading your replies, thanks. I had my filters in the wrong order -- I was cropping first then trying to resize. Now that I got the aspect ratio stuff sorted, I reversed my filter orders. I first resize appropriately, then crop the bars off. Works great.