[MPlayer-users] -ss Does it work? Also bpp. Bunkus explain maybe?

[D Richard Felker III]

On Sun, Jan 12, 2003 at 10:22:52PM -0500, Geoffrey Trexler wrote:
> Ok well I don't have much of a choice with the vob's because I don't
> have the DVD anymore, perhaps I can cat them into one big vob, and
> bypass the |.
> 
> About the not using the script right, I looked at my prescale thing,
> and it said 1.78:1. Here's that line Movie-Aspect is 1.78:1 -
> prescaling to correct movie aspect. 720x466 is what I got from crop
> detect. I found the 29.97 from -v with mplayer. The 1608 being the
> bitrate. So I used perl ../../calcbpp.pl 720x466 1.78 1608 29.97 Is
> this not the correct way to use it?

1.78:1 is probably the aspect before cropping. You'll have to adjust
it for your cropping parameters. Oh also, if this is an NTSC (USA)
DVD, the 29.97 fps is bogus and will seriously mess up the quality of
your encode. Use -ofps 23.976 to fix it. Read the archives if you want
to read many detailed explanations of the reason.

> Here's a few lines from cropdetect
> 
> crop area: X: 0..719  Y: 4..470  (-vop crop=720:466:0:4)6%  5.7% 0 0 0%
> crop area: X: 0..719  Y: 4..470  (-vop crop=720:466:0:4)6%  5.7% 0 0 0%
> crop area: X: 0..719  Y: 4..470  (-vop crop=720:466:0:4)6%  5.7% 0 0 0%
> crop area: X: 0..719  Y: 4..470  (-vop crop=720:466:0:4)6%  5.7% 0 0 0%
> crop area: X: 0..719  Y: 4..470  (-vop crop=720:466:0:4)6%  5.6% 0 0 0%
> crop area: X: 0..719  Y: 4..470  (-vop crop=720:466:0:4)6%  5.6% 0 0 0%
> crop area: X: 0..719  Y: 4..470  (-vop crop=720:466:0:4)6%  5.6% 0 0 0%
> crop area: X: 0..719  Y: 4..470  (-vop crop=720:466:0:4)6%  5.6% 0 0 0%
> crop area: X: 0..719  Y: 4..470  (-vop crop=720:466:0:4)6%  5.6% 0 0 0%
> crop area: X: 0..719  Y: 4..470  (-vop crop=720:466:0:4)6%  5.6% 0 0 0%
> 
> So with this information how would I use the cropping filter? I'm
> new to this so these questions may seem quite stupid to you. I've
> looked at the man page on this, but I can't really understand it.

Well you could just use -vop crop=720:466:0:4.

But that might be leaving a slight border still. So you might try -vop
crop=716:462:2:6 or something (removing 2 more pixels from all four
sides).

Now you want to make sure width and height are multiples of 16. To do
this you could crop down smaller and lose some of the picture, but it
probably makes more sense to scale anyway, since it's hard to get
great quality at such high res.

I'm not thinking too straight right now though so I won't try to work
out how to correct aspect, scale down proportionately, and keep width
and height multiples of 16 right now. Hopefully someone else will post
a reply or I'll feel more logical later. I think there's actually a
way to automate it with the right filter options.

Read some of the archives for discussions like this in the past if you
want to learn more.

Rich