First off a black boarder represents a hard transition. Encoding that transition with a combination of 2 dimensional cosine functions (if i'm remembering the theory correctly) is hard and thus wastes bandwidth. Take a look at sharp transitions, like text, in mpeg videos with low bit rates and you will see this effect.
The exception is if you manage to make the black bars occur such that it falls on a 16x8 or 16x16 or whatever the block size of the underlying codec is. That way very little bandwidth is wasted. Also you may need to keep them to maintain your aspect ratio. Also resizing the video has its own losses, so its sometimes not obvious if its best to cut them or not. If you don't mind keeping the bitrate relatively high then they really aren't hurting anything, so it becomes a mater of personal preferance.
Vijay Gill wrote:
Hi,
I use mythtv + PVR350 to capture the programs and edit them to
create cutlists(for removing commercials). Then I use combination of
mythtranscode + mencoder to get MPEG2 which I burn on DVDs.
Now I have seen that there is a small black border on left and
right sides of the image (NOT top and bottom, but left and right). I
can remove it by using the crop filter in mencoder. My questions is :
Should I do it? Is that border there because of some reason (may be
represents some non-displayable area of image, which if I remove, may
start eating some portion of my actual program image)?
Regards from
VJ
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