This may be a bit off topic, but I am hoping that someone might be able to help
me to better understand the new way of cropping video.
Typically, the original video is one of .MPG, .AVI or .VOB and the usual size
is 720X480 with an aspect ratio of 4:3 (at least according to the properties I
can discern). Depending upon the original source, the actual part of the video
that I want may be:
4:3 filling the whole frame4:3 but not filling the whole frame, centred16:9
filling the width of the frame with black bands at top and bottom, centred
vertically
16:9 not filling the whole frame with black bands at top, bottom, left and
right, centred both horizontally and vertically.Situation 1 is no problem --
just keep things as they are for editing, etc.
In case 3 above, I used to use croptop={size of black band} cropbottom={size of
black band} with -aspect 16:9
In the other two cases, I would add cropleft and cropright. For case 2 I would
use -aspect 4:3 and for 4, -aspect 16:9
In all of these, I would end up with the video filling the frame with the
appropriate aspect ratio.
I have read the man pages, looked at lots of descriptions on the net, but still
have not figured out how to do the same thing with the new "-vf crop=h:w:x:y".
I have tried lots of combinations, but everything I have tried so far
(especially when original had black bands both vertically and horizontally)
seems to just move the video around within the larger frame but keeping the
black bands. I am using -s hd720 to create a 1280X720 HD video.
Perhaps I need to do something different to fill the frame. Here is an example
of a command I used to try to do this; perhaps someone can tell me what I am
missing:
ffmpeg -i input.mpg -vf crop=in_w:in_h-32:0:0 -t 150 -s hd720 -b 8500k
output.mpg
input.mpg was 720X480 with the 16:9 aspect active video centred.in the 4:3
frame with black borders. The resulting output was 1280:720 16:9 with the video
shifted down, but still not filling the frame.
Thanks for any help.
Murray
