Should black bars be cropped when backing up Blu-ray and DVD movies?

[orion44]

Do you crop black bars when backing up Blu-ray and DVD movies?

Does cropping the black bars decrease video quality?

[Boulder]

I always crop. It does not decrease quality but will rather increase it because the bits will then be spent on the active area of the frame. Sometimes there is noise also in the border area, at least near the edges.

[tormento]

It depends.

Consider that if you have a "stupid" player on your tv, it will resize the movie, losing quality.

So, I tend to ignore small black bars to reach 1920 widht or 1080 height.

If the bars are noticeable, I crop.

[wonkey_monkey]

Is it worth keeping crops to mod 16 so that macroblocks occupy the same positions in the re-encode?

[tormento]

Originally Posted by wonkey_monkey

Is it worth keeping crops to mod 16 so that macroblocks occupy the same positions in the re-encode?

I keep mod8, usually. After a denoise, it's not worth worrying about macroblocks.

[StainlessS]

If you want to keep borders, not a bad idea to use Letterbox() on them, ie make perfect black borders.
http://avisynth.nl/index.php/Letterbox

Letterbox(clip clip, int top, int bottom [, int x1 , int x2 , int color ] [, int color_yuv AVS+])

    int  top, bottom = (required)

        Number of top and bottom rows to blank out.

            For YV12 sources, top and bottom must be mod2 (divisible by 2). 

    int  x1, x2 = 0

        Number of left (x1) and right (x2) columns to blank out.

            For YUY2, YV16 and YV12 sources, left and right must be mod2 (divisible by 2).
            For YV411 sources, left and right must be mod4 (divisible by 4). 

    int  color = (black)

        Fill color; specified as an RGB value. See this page for more information on specifying colors.

            For YUV clips, colors are converted from full-range (0d-255d) to YV-range (16d-235d). 

    int  color_yuv =
    AVS+

        Specifies the color of the border using YUV values. It requires setting pixel_type to one of the YUV formats; otherwise it doesn't do anything. 
        Similar to color_yuv in BlankClip

Usually use the default 16 for YUV

[Sharc]

Originally Posted by wonkey_monkey

Is it worth keeping crops to mod 16 so that macroblocks occupy the same positions in the re-encode?

Hmmm.... I think to remember that the quality decreases slightly near the borders with respect to the rest of the macroblock (the encoder uses higher quantizers) unless one keeps the original mod 16 macroblock structure intact. It may happen only when one adds 'misaligned' clean black borders back though (?). It's probably because the encoder distributes the bits differently when part of the macroblock is black compared to when the full macroblock is used by the picture. The difference is small anyway and barely noticeable.

@orion44: Just in case you want to author blu-ray or DVD discs you must keep the borders.

[Groucho2004]

For BD movies, I pretty much always keep the bars. I also almost always resize to 720p since very few movies have the actual resolution worth keeping them at their original 1080p. There are exceptions such as Wall-E from Pixar which really uses the full 1080p resolution.

For DVD, I usually crop the bars since sometimes they have kinda fuzzy margins. However, after cropping I add bars again and resize to 1024 x 576 for 1:1 PAR.

I compared encoding with/without bars and never encountered any significant bitrate differences for a given CRF.

[Boulder]

Originally Posted by Sharc

It's probably because the encoder distributes the bits differently when part of the macroblock is black compared to when the full macroblock is used by the picture.

A modern encoder (like x264 or x265) can skip those completely black blocks so the bitrate needed for them in the bitstream is very low. That's why it's important to at least make sure they are only black and no (invisible to the human eye) noise there.