Bugs item #1591170, was opened at 2006-11-06 07:54
Message generated for change (Comment added) made by duncanwebb
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Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Pierre Ossman (dr7eus)
Assigned to: Nobody/Anonymous (nobody)
Summary: Autocrop needs more samples

Initial Comment:
The autocrop feature sometimes gets things very, very
wrong. The problem is that it looks at such a short
part of a movie, so it's easily fooled.

Simply increasing the number of frames is not a viable
solution as the scene in the movie is probably similar
in that problem area. What we need is samples from more
locations in the file.

Either we start mplayer multiple times, or we get it to
seek. I'm not familiar with how to control mplayer via
commands, so I do not know how to do the latter. But
someone else perhaps has this know-how :)

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>Comment By: Duncan Webb (duncanwebb)
Date: 2006-11-06 14:08

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Another way is to use:
mplayer -vo null -ao null -ss 180 -sstep 60 -vf cropdetect
/path/to/file but it's a lot slower.

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Comment By: Pierre Ossman (dr7eus)
Date: 2006-11-06 13:41

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That won't solve the problem. The issue is that with such a
short sample (20 frames), we have a high risk of getting
incorrect crop dimensions (because of a dark scene). What we
need is to increase the number of samples and to do that
efficiently we would need to seek.

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Comment By: Duncan Webb (duncanwebb)
Date: 2006-11-06 13:04

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A bit tricky if an ad break is scanned as they ususally have
different crop, some shows start and then almost immediately
have an ad break.

One solution is for the -ss command to be
TV_RECORD_PADDING_PRE * 2

Here is an untested patch, you could test it :-)

-ss <time> (also see -sb)
Seek to given time position.
EXAMPLE:
 -ss 56
  Seeks to 56 seconds.
 -ss 01:10:00
  Seeks to 1 hour 10 min.

Also:
 -sstep <sec>
   Skip  <sec> seconds after every frame.  The normal
framerate of the movie is kept, so playback is accelerated.
 Since MPlayer can only seek to the next keyframe this may
be inexact.

A bit of trial and error here, but there may not be an ideal
solution.


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