$ ffmpeg -i clip.mp4 -c:v libvpx -b:v 1M -c:a libvorbis output.webm

ffmpeg version 2.6.8 Copyright (c) 2000-2016 the FFmpeg developers
  built with gcc 4.8.5 (GCC) 20150623 (Red Hat 4.8.5-4)
  configuration: --prefix=/usr --bindir=/usr/bin --datadir=/usr/share/ffmpeg --incdir=/usr/include/ffmpeg --libdir=/usr/lib64 --mandir=/usr/share/man --arch=x86_64 --optflags='-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic' --enable-bzlib --disable-crystalhd --enable-gnutls --enable-ladspa --enable-libass --enable-libcdio --enable-libdc1394 --enable-libfaac --enable-nonfree --enable-libfdk-aac --enable-nonfree --disable-indev=jack --enable-libfreetype --enable-libgsm --enable-libmp3lame --enable-nvenc --enable-nonfree --extra-cflags=-I/usr/include/nvenc --enable-openal --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libvorbis --enable-libv4l2 --enable-libx264 --enable-libx265 --enable-libxvid --enable-x11grab --enable-avfilter --enable-avresample --enable-postproc --enable-pthreads --disable-static --enable-shared --enable-gpl --disable-debug --disable-stripping --shlibdir=/usr/lib64 --enable-runtime-cpudetect
  libavutil      54. 20.100 / 54. 20.100
  libavcodec     56. 26.100 / 56. 26.100
  libavformat    56. 25.101 / 56. 25.101
  libavdevice    56.  4.100 / 56.  4.100
  libavfilter     5. 11.102 /  5. 11.102
  libavresample   2.  1.  0 /  2.  1.  0
  libswscale      3.  1.101 /  3.  1.101
  libswresample   1.  1.100 /  1.  1.100
  libpostproc    53.  3.100 / 53.  3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from './f61321ad59d38307b78f35266bf69455/tmp.NJalCCOfsQ/clip.mp4':
  Metadata:
    major_brand     : avc1
    minor_version   : 0
    compatible_brands: isomavc1
    creation_time   : 2016-03-27 20:07:54
  Duration: 00:00:13.88, start: 0.000000, bitrate: 313 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 280x180, 310 kb/s, 29.97 fps, 29.97 tbr, 2997 tbn, 59.94 tbc (default)
    Metadata:
      creation_time   : 2016-03-27 20:07:54
      handler_name    : GPAC ISO Video Handler
Unknown encoder 'libvpx'

# rpm -qa | grep -e vpx -e ffmpeg
libvpx-1.3.0-5.el7_0.x86_64
libvpx-devel-1.3.0-5.el7_0.x86_64
ffmpeg-2.6.8-1.el7.nux.x86_64
ffmpeg-libs-2.6.8-1.el7.nux.x86_64
libvpx-utils-1.3.0-5.el7_0.x86_64

ffmpeg -i Video.mp4 -c:a copy -vf cropdetect=24:16:0 tmp.mp4

This command worked correctly on el6 and el7, and I get
no errors when run on el6.  Since I accidentally erased
and then reinstalled several packages on el7, I now get
this in the output.

Stream mapping:
  Stream #0:0 -> #0:0 (h264 (native) -> h264 (nvenc))
  Stream #0:1 -> #0:1 (copy)
Error while opening encoder for output stream #0:0 - maybe incorrect
parameters such as bit_rate, rate, width or height

ffmpeg -i vodafonexmas.mp4 vodafonexmas2.mp4
ffmpeg version 2.6.8 Copyright (c) 2000-2016 the FFmpeg developers
  built with gcc 4.8.5 (GCC) 20150623 (Red Hat 4.8.5-4)
  configuration: --prefix=/usr --bindir=/usr/bin --datadir=/usr/share/ffmpeg --incdir=/usr/include/ffmpeg --libdir=/usr/lib64 --mandir=/usr/share/man --arch=x86_64 --optflags='-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic' --enable-bzlib --disable-crystalhd --enable-gnutls --enable-ladspa --enable-libass --enable-libcdio --enable-libdc1394 --enable-libfaac --enable-nonfree --enable-libfdk-aac --enable-nonfree --disable-indev=jack --enable-libfreetype --enable-libgsm --enable-libmp3lame --enable-nvenc --enable-nonfree --extra-cflags=-I/usr/include/nvenc --enable-openal --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libvorbis --enable-libv4l2 --enable-libx264 --enable-libx265 --enable-libxvid --enable-x11grab --enable-avfilter --enable-avresample --enable-postproc --enable-pthreads --disable-static --enable-shared --enable-gpl --disable-debug --disable-stripping --shlibdir=/usr/lib64 --enable-runtime-cpudetect
  libavutil      54. 20.100 / 54. 20.100
  libavcodec     56. 26.100 / 56. 26.100
  libavformat    56. 25.101 / 56. 25.101
  libavdevice    56.  4.100 / 56.  4.100
  libavfilter     5. 11.102 /  5. 11.102
  libavresample   2.  1.  0 /  2.  1.  0
  libswscale      3.  1.101 /  3.  1.101
  libswresample   1.  1.100 /  1.  1.100
  libpostproc    53.  3.100 / 53.  3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'vodafonexmas.mp4':
  Metadata:
    major_brand     : mp42
    minor_version   : 0
    compatible_brands: isommp42
    creation_time   : 2015-11-30 13:19:25
  Duration: 00:01:00.00, start: 0.000000, bitrate: 1502 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 1280x720 [SAR 1:1 DAR 16:9], 1307 kb/s, 25 fps, 25 tbr, 25 tbn, 50 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 191 kb/s (default)
    Metadata:
      creation_time   : 2015-11-30 13:19:25
      handler_name    : IsoMedia File Produced by Google, 5-11-2011
[nvenc @ 0xd6aac0] Failed loading CUDA library
Output #0, mp4, to 'vodafonexmas2.mp4':
  Metadata:
    major_brand     : mp42
    minor_version   : 0
    compatible_brands: isommp42
    Stream #0:0(und): Video: h264, none, q=2-31, 128 kb/s, SAR 1:1 DAR 0:0, 25 fps (default)
    Metadata:
      handler_name    : VideoHandler
      encoder         : Lavc56.26.100 nvenc
    Stream #0:1(eng): Audio: aac, 0 channels, 128 kb/s (default)
    Metadata:
      creation_time   : 2015-11-30 13:19:25
      handler_name    : IsoMedia File Produced by Google, 5-11-2011
      encoder         : Lavc56.26.100 libfaac
Stream mapping:
  Stream #0:0 -> #0:0 (h264 (native) -> h264 (nvenc))
  Stream #0:1 -> #0:1 (aac (native) -> aac (libfaac))
Error while opening encoder for output stream #0:0 - maybe incorrect parameters such as bit_rate, rate, width or height