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

[Krister Lagerstrom]

D Richard Felker III wrote:

> 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.

It is a little tricky. Here is a tiny python app that runs mplayer with
cropdetect on the DVD and tries to figure out the crop and scale
parameters. I've just written it and only tested it a few times, so
please double-check the results and let me know if there any problems
(it might be doing something braindead :-).

It is intended to crop out the black borders and as many of the lines
that can fit in an even multiple of 16, but scale the width to keep the
aspect ratio so it can be played with any program. It could be fixed to
add a margin to the cropping as you suggested, to take multiple samples
of the DVD with cropdetect, and to scale both height and width if the
total number of pixels is too big for the bitrate.

To run the script, just save it and type "python dvd_cropscale.py".
I've only tried it with python 2.2, you might have to use python2 on
Red Hat.

		/ Krister
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#if 0 /*
# -----------------------------------------------------------------------
# dvd_cropscale.py - Calculate crop and scale params for DVD backups
# -----------------------------------------------------------------------
# $Id: fileheader,v 1.2 2002/08/14 04:33:54 krister Exp $
#
# Notes:
# Todo:        
#
# -----------------------------------------------------------------------
# $Log: fileheader,v $
#
# -----------------------------------------------------------------------
# Freevo - A Home Theater PC framework
# Copyright (C) 2002 Krister Lagerstrom, et al. 
# Please see the file freevo/Docs/CREDITS for a complete list of authors.
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of MER-
# CHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
# Public License for more details.
#
# You should have received a copy of the GNU General Public License along
# with this program; if not, write to the Free Software Foundation, Inc.,
# 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
#
# ----------------------------------------------------------------------- */
#endif


import os
import sys
import commands
import re


def main():

    # The DVD title is 1 by default, or can be given as the first argument
    title = 1
    if len(sys.argv) >= 2:
        title = int(sys.argv[1])

    # The test clip position is 0:15:0 by default, or can be given as the second argument
    pos = '0:15:00'
    if len(sys.argv) >= 3:
        pos = sys.argv[2]

    cmd = 'mplayer -quiet -dvd %s -vo null -ao null -vop cropdetect -frames 30 -ss %s 2> /dev/null' % (title, pos)
    status, output = commands.getstatusoutput(cmd)

    if status:
        print 'Error:', status
        sys.exit()

    # Parsed settings
    aspect = None
    crop = None
    
    lines = output.split('\n')
    for line in lines:

        # Check for base geometry
        m = re.match(r'VIDEO:\s+MPEG2\s+(\d+)x(\d+)\s+\(aspect (\d)\).*', line)
        if m and m.groups()[:2] != ('720', '480'):
            print 'Can only handle base geometry 720x480! Got %s)' % m.groups()[:2]
            sys.exit()
        elif m:
            # Aspect 0=1.33, 3=1.78
            if m.groups()[2] == '2':
                aspect = 1.33
            else:
                aspect = 1.78

        # Check for crop results
        m = re.match(r'[^(]+\(-vop crop=(\d+):(\d+):(\d+):(\d+)\).*', line)
        if m:
            # Is this the largest crop setting so far?
            w, h, x0, y0 = map(lambda s: int(s), m.groups())
            if not crop or (w, h, x0, y0) > crop:
                crop = w, h, x0, y0


    print 'Aspect: %s' % aspect
    print 'Cropvals: %s' % list(crop)
    print

    w, h, x0, y0 = crop

    # Calculate number of lines (=height=y) as the closest lower number
    # divisible by 16
    new_h = (h / 16) * 16

    # New start line
    new_y0 = y0 + (h - new_h) / 2

    # Ok, now we got the crop values. Calculate the scaling so that
    # the aspect ratio is correct, and the number of pixels on the line
    # is divisible by 16.
    
    # Scaling. The aspect on the disc is 1.5 (720/480), correct for that.
    scale_x = aspect / 1.5
    new_w = w * scale_x

    # Adjust to the closest modulo 16
    new_w = int(round(new_w / 16.0) * 16)

    args = (new_w, new_h, w, new_h, x0, new_y0)
    print 'Settings: -vop scale=%s:%s,crop=%s:%s:%s:%s' % args

    print 'Original aspect = %1.2f, new = %1.2f' % (aspect, (float(new_w) / new_h) )
    
            

if __name__ == '__main__':
    main()