ffmpeg -i tes1.avi -vf pad=420:1080:0:0:black test1.avi
ffmpeg version 0.10.6-6:0.10.6-0ubuntu0jon1~precise1 Copyright (c) 2000-2012 the FFmpeg developers
  built on Nov 12 2012 13:11:38 with gcc 4.6.3
  configuration: --arch=amd64 --enable-pthreads --enable-runtime-cpudetect --extra-version='6:0.10.6-0ubuntu0jon1~precise1' --libdir=/usr/lib/x86_64-linux-gnu --disable-stripping --prefix=/usr --enable-bzlib --enable-libdc1394 --enable-libfreetype --enable-frei0r --enable-gnutls --enable-libgsm --enable-libmp3lame --enable-librtmp --enable-libopencv --enable-libopenjpeg --enable-libpulse --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-vaapi --enable-vdpau --enable-libvorbis --enable-libvpx --enable-zlib --enable-gpl --enable-postproc --enable-libcdio --enable-x11grab --enable-libx264 --shlibdir=/usr/lib/x86_64-linux-gnu --enable-shared --disable-static
  libavutil      51. 35.100 / 51. 35.100
  libavcodec     53. 61.100 / 53. 61.100
  libavformat    53. 32.100 / 53. 32.100
  libavdevice    53.  4.100 / 53.  4.100
  libavfilter     2. 61.100 /  2. 61.100
  libswscale      2.  1.100 /  2.  1.100
  libswresample   0.  6.100 /  0.  6.100
  libpostproc    52.  0.100 / 52.  0.100
[h264 @ 0x218b420] Increasing reorder buffer to 1
[avi @ 0x217b680] max_analyze_duration 5000000 reached at 5000000
Input #0, avi, from 'tes1.avi':
  Metadata:
    encoder         : Lavf53.32.100
  Duration: 00:00:15.84, start: 0.000000, bitrate: 2413 kb/s
    Stream #0:0: Video: h264 (Main) (avc1 / 0x31637661), yuv420p, 1080x1080, 25 fps, 25 tbr, 25 tbn, 50 tbc
[buffer @ 0x2213c80] w:1080 h:1080 pixfmt:yuv420p tb:1/1000000 sar:0/1 sws_param:
[pad @ 0x22147e0] w:1080 h:1080 -> w:420 h:1080 x:0 y:0 color:0x108080FF[yuva]
[pad @ 0x22147e0] Input area 0:0:1080:1080 not within the padded area 0:0:420:1080 or zero-sized
Error opening filters!