Frustrated "pad" usage per poor documentation

[elias tsolis]

I found it very frustrating to center a video
the original dimensions was: Width 1920 pixels and Height : 1080 pixels. I wanted to make new dimensions with padding as: (h)3840x(w)2160

I found these problems
if i put height/2 or iw/2 or ow/2 are not recognised.
I could not understand when iw ow or height can be interpret and when not. There are not taken automatically from videofile? I must define explicity somewhere these variables?
What is the diff between "=" and ":"?

for eg.
this works
"pad=width=2160:height=3840:x=3840/2:y=2160/2:color=red"
this does not work
"pad=width=2160:height=3840:x=width/2:y=height/2:color=red"
"pad=width=2160:height=3840:x=iw/2:y=ih/2:color=red"
"pad=iw=2160:ih=3840:x=iw/2:y=ih/2:color=red"
"pad=iw:2160:ih:3840:x=iw/2:y=ih/2:color=red"

This was very frustrated for me.
you explicity says in your manual:

"in_w
in_h

The input video width and height.

iw
ih

These are the same as in_w and in_h.

"

Also i cant understand when to use "()" for expressions and when not.
You must explicity explain in your manual these things.
I spent almost 4 hours+ to nothing.

This works:

rm a_t.mp4; for vids in *.mkv; do ffmpeg -i "$vids" -ss 0:00:00 -to 00:00:01  -vf  "pad=width=2160:height=3840:x=3840/2:y=2160/2:color=red"  -video_track_timescale 90000 -crf 19  -vcodec libx265   -an "a_${vids/.*}.mp4"; done;

this does not:

rm a_t.mp4; for vids in *.mkv; do ffmpeg -i "$vids" -ss 0:00:00 -to 00:00:01  -vf  "pad=width=2160:height=3840:x=height/2:y=width/2:color=red"  -video_track_timescale 90000 -crf 19  -vcodec libx265   -an "a_${vids/.*}.mp4"; done;

ffmpeg --version
ffmpeg version N-115575-g4e120fbbbd Copyright (c) 2000-2024 the FFmpeg developers
  built with gcc 13 (Debian 13.2.0-25)
  configuration: --prefix=/home/eros/ffmpeg_build --pkg-config-flags=--static --extra-cflags=-I/home/eros/ffmpeg_build/include --extra-ldflags=-L/home/eros/ffmpeg_build/lib --extra-libs='-lpthread -lm' --ld=g++ --bindir=/home/eros/bin --enable-gpl --enable-gnutls --enable-libaom --enable-libass --enable-libfreetype --enable-libmp3lame --enable-libopus --enable-libsvtav1 --enable-libdav1d --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-nonfree
  libavutil      59. 21.100 / 59. 21.100
  libavcodec     61.  6.100 / 61.  6.100
  libavformat    61.  3.104 / 61.  3.104
  libavdevice    61.  2.100 / 61.  2.100
  libavfilter    10.  2.102 / 10.  2.102
  libswscale      8.  2.100 /  8.  2.100
  libswresample   5.  2.100 /  5.  2.100
  libpostproc    58.  2.100 / 58.  2.100

[Michael Koch]

Replying to elias tsolis:

this does not work
"pad=width=2160:height=3840:x=width/2:y=height/2:color=red"
"pad=width=2160:height=3840:x=iw/2:y=ih/2:color=red"

Your second example has the correct syntax and works for me:
ffmpeg -f lavfi -i testsrc2=s=1920x1080 -vf "pad=width=2160:height=3840:x=iw/2:y=ih/2:color=red" -y out.png

[Michael Koch]

You can simplify the command if you specify the parameters in the correct order (as listed in the documentation):
"pad=2160:3840:iw/2:ih/2:red"

[MasterQuestionable]

͏    In filter description:
͏    ":" as the separator of options.
͏    "=" as the name-value separator of each option.

͏    See also:
͏    https://ffmpeg.org/ffmpeg-filters.html#Filtergraph-syntax-1


͏    Usage of parentheses mostly follows their typical definition in other programming languages: merely as priority/associativity override.


͏    The doc is indeed horrible to some extent.
͏    However due to the framed choice of rendering scheme (Texinfo) that few would understand how to properly write:
͏    Fix may not be easy.

[elias tsolis]

weird what worked for you not worked for me and what didnt work for you worked for me.
What ffmpeg edition you have and in what software? Linux?

[MasterQuestionable]

͏    See also:
͏    ​https://trac.ffmpeg.org/wiki/Scaling#fit

[elias tsolis]

why in the example of link uses double parenthensis?

pad=320:240:(( (ow - iw)/2 )):(( (oh - ih)/2 ))

[MasterQuestionable]

͏    Why don't we write everything in one-liner and get rid of comments?..

͏    The "(( ... ))" concept is derived from Unix "$(( ... ))":
͏    ​https://pubs.opengroup.org/onlinepubs/9699919799.2018edition/utilities/V3_chap02.html#tag_18_06_04
͏    ​https://www.google.com/search?hl=en&gl=ca&num=100&q=site:pubs.opengroup.org/onlinepubs/9699919799+-intitle:%22Index+of+/onlinepubs%22+-inurl:idx+-inurl:contents.html+-inurl:toc.html+-inurl:9699919799.orig+-inurl:2008edition+-inurl:2013edition+-inurl:2016edition+-inurl:2018edition+%22Arithmetic+Expansion%22