How install ffmpeg package 7:3.4.2-2build2 and ffmpeg install package in https://trac.ffmpeg.org/wiki/CompilationGuide/Ubuntu.

When I convert a movie to the following error message. How should I fix it?

ffmpeg -i test.avi -vcodec libx264 -s 640x360 -threads 4 -movflags faststart test.mp4

ffmpeg version 2.8.14-0ubuntu0.16.04.1 Copyright (c) 2000-2018 the FFmpeg developers
  built with gcc 5.4.0 (Ubuntu 5.4.0-6ubuntu1~16.04.9) 20160609
  configuration: --prefix=/usr --extra-version=0ubuntu0.16.04.1 --build-suffix=-ffmpeg --toolchain=hardened --libdir=/usr/lib/i386-linux-gnu --incdir=/usr/include/i386-linux-gnu --cc=cc --cxx=g++ --enable-gpl --enable-shared --disable-stripping --disable-decoder=libopenjpeg --disable-decoder=libschroedinger --enable-avresample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmodplug --enable-libmp3lame --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-librtmp --enable-libschroedinger --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxvid --enable-libzvbi --enable-openal --enable-opengl --enable-x11grab --enable-libdc1394 --enable-libiec61883 --enable-libzmq --enable-frei0r --enable-libx264 --enable-libopencv --disable-i686
  libavutil      54. 31.100 / 54. 31.100
  libavcodec     56. 60.100 / 56. 60.100
  libavformat    56. 40.101 / 56. 40.101
  libavdevice    56.  4.100 / 56.  4.100
  libavfilter     5. 40.101 /  5. 40.101
  libavresample   2.  1.  0 /  2.  1.  0
  libswscale      3.  1.101 /  3.  1.101
  libswresample   1.  2.101 /  1.  2.101
  libpostproc    53.  3.100 / 53.  3.100
Input #0, avi, from 'test.avi':
    encoder         : MEncoder 2:1.0~rc2-0ubuntu13
  Duration: 00:09:56.46, start: 0.000000, bitrate: 2099 kb/s
    Stream #0:0: Video: msmpeg4v2 (MP42 / 0x3234504D), yuv420p, 854x480, 1840 kb/s, 24 fps, 24 tbr, 24 tbn, 24 tbc
    Stream #0:1: Audio: mp3 (U[0][0][0] / 0x0055), 48000 Hz, stereo, s16p, 245 kb/s
[libx264 @ 0x9298700] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX
[libx264 @ 0x9298700] profile High, level 3.0
[libx264 @ 0x9298700] 264 - core 148 r2643 5c65704 - H.264/MPEG-4 AVC codec - Copyleft 2003-2015 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 threads=4 lookahead_threads=1 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1 b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=24 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
[aac @ 0x9299820] **The encoder 'aac' is experimental but experimental codecs are not enabled, add '-strict -2' if you want to use it.**
  • 1
    You're using ffmpeg from the repository, not a compiled ffmpeg.
    – llogan
    Jun 19, 2018 at 19:01

1 Answer 1


Immediate issue

This is a problem with your usage of FFmpeg, not its compilation from source. The last line of the program output reads:

The encoder aac is experimental but experimental codecs are not enabled, add -strict -2 if you want to use it.

If you change the invocation options as suggested in the error message the operation should run as intended (with the given caveat):

ffmpeg -i test.avi -vcodec libx264 -s 640x360 -threads 4 -movflags faststart -strict -2 test.mp4

Lord Neckbeard points out that the option needs to be applied to the output, not the input.

Alternative solution

There is little benefit in transcoding the lossy MP3 audio stream to a lossy AAC audio stream unless the target device doesn't play back MP3 for some reason. Instead you can instruct FFmpeg to copy the audio stream as it is with the -codec:a copy setting:

ffmpeg -i test.avi -codec:v libx264 -s 640x360 -threads 4 -movflags faststart -codec:a copy test.mp4
  • As you’ve never accepted an answer before: if this answers your question, don’t forget to click the grey ☑ under the number at the left of this text to accept it, which means “yes, this answer is valid”! Jun 19, 2018 at 17:18
  • 1
    Option order is important: ffmpeg [input options] -i input [output options] output. You're trying to apply -strict -2 to the input, but this is an output option (it may still work however, but it is something to keep in mind). Recent ffmpeg versions no longer need -strict -2 (or the alias -strict experimental), so if this ancient version is updated then that option can be removed.
    – llogan
    Jun 19, 2018 at 19:05

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.