cropped vertical res. must be n*16?

[20/20]

Hi,

In Megui, If I setup the XY-res. And its a perfect 16:9
Then go to cropping to remove black bars.
Must I always crop away in mutliple of 16 pixels to not destroy the perfect 16:9
resolution?

I dont understand this. When I crop using multiple of 16 pixels,
I cannot remove ALL of the black bars ofcourse.
Cuz I will always be left with black bars that are a few pixels in width...
Or did I get it all wrong?

Help?

[redwudz]

Some codecs have restrictions. Divx says: 'Width must be multiple of 4, Height must be a multiple of 2, Valid depths: 24 32'. Xvid says: 'No known restrictions'. Other codecs may also have some restrictions for framesize.

I opened VirtualDub Mod and it showed these restrictions when I chose a codec.

[jagabo]

Xvid says "no restrictions" but the width and height must be a multiple of 2.

I don't know Megui but I suspect it forces multiples of 16 because that is most efficient for MPEG 1/2/4 codecs (because they use 16x16 macroblocks).

Removing borders is inadvisable if you ever plan to watch on TV.

[manono]

It's usually best (depending on colorspace and progressive/interlaced restrictions) to crop by multiples of 2 pixels. It's best (for encoder efficiency reasons) to resize in multiples of 16 pixels. I disagree with the notion of leaving any black at all.

[celtic_druid]

Crop, then resize. Or better yet, just crop and set the AR instead of resizing.

[20/20]

Thanks for the effort in trying to help a newbie guys :P

Crop, then resize. Or better yet, just crop and set the AR instead of resizing.

So the "AR" is a flag then, within a videofile? <-- didnt knew that.

So what you're saying is, I can crop to codec-specifications (*2 or *4 *16 * or *32)
And set a flag wich will AR-resize it to the correct AR during play??

This video-hobby will consume loads of time if I want to learn everyhting correctly.

Removing borders is inadvisable if you ever plan to watch on TV.

Is that so? Mmm. I have yet much to learn and understand I see.
I read a guide somewhere that even advised to crop i little "inwards" intp the picture
before encoding.

[redwudz]

Some guides may tell you to crop the video head switching noise off at the bottom of a VHS capture, but it doesn't show on most TVs. The thought is that the noise wastes extra bitrate to encode. A better recommendation in the VHS capture case may be to mask it instead if you want to save bitrate. Other than that type of obvious noise, I wouldn't crop a small amount off a video without a good reason as you may end up resizing unnecessarily.

There is also overscan to consider, which on most TVs hides ~5% or a little more of the edges of the screen that you would normally see on a computer monitor.

[celtic_druid]

Always best to crop borders and yes that can mean cropping into the picture to keep a mod16 resolution if you aren't resizing.

Above is purely from an encoding point of view. Playback is someone else's problem and work arounds of any kind just suck. Overscan isn't an issue here at least anyway (Ubuntu based PC used for playback on an LCD TV).