ffmpeg -i test.mp4 -i audio.mp3 -filter_complex "[0]asetnsamples=8192[a];[1]asetnsamples=8192[b];[a][b]amix=inputs=2:duration=first:dropout_transition=0" -report  output.mp4
ffmpeg started on 2017-07-18 at 13:21:17
Report written to "ffmpeg-20170718-132117.log"
ffmpeg version 3.3.2 Copyright (c) 2000-2017 the FFmpeg developers
  built with Apple LLVM version 8.1.0 (clang-802.0.42)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/3.3.2 --enable-shared --enable-pthreads --enable-gpl --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-libass --enable-libfdk-aac --enable-libfreetype --enable-libmp3lame --enable-libx264 --enable-libxvid --enable-opencl --disable-lzma --enable-nonfree --enable-vda
  libavutil      55. 58.100 / 55. 58.100
  libavcodec     57. 89.100 / 57. 89.100
  libavformat    57. 71.100 / 57. 71.100
  libavdevice    57.  6.100 / 57.  6.100
  libavfilter     6. 82.100 /  6. 82.100
  libavresample   3.  5.  0 /  3.  5.  0
  libswscale      4.  6.100 /  4.  6.100
  libswresample   2.  7.100 /  2.  7.100
  libpostproc    54.  5.100 / 54.  5.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'test.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf57.71.100
  Duration: 00:00:03.11, start: 0.000000, bitrate: 500 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 480x360 [SAR 1:1 DAR 4:3], 362 kb/s, 30 fps, 30 tbr, 15360 tbn, 60 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 127 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
[mp3 @ 0x7ffb8a010800] Estimating duration from bitrate, this may be inaccurate
Input #1, mp3, from 'audio.mp3':
  Metadata:
    major_brand     : dash
    minor_version   : 0
    compatible_brands: iso6mp41
    encoder         : Lavf57.19.100
  Duration: 00:03:13.62, start: 0.000000, bitrate: 192 kb/s
    Stream #1:0: Audio: mp3, 44100 Hz, stereo, s16p, 192 kb/s
File 'output.mp4' already exists. Overwrite ? [y/N] y
Stream mapping:
  Stream #0:1 (aac) -> asetnsamples (graph 0)
  Stream #1:0 (mp3) -> asetnsamples (graph 0)
  amix (graph 0) -> Stream #0:0 (aac)
  Stream #0:0 -> #0:1 (h264 (native) -> h264 (libx264))
Press [q] to stop, [?] for help
[libx264 @ 0x7ffb89809200] using SAR=1/1
[libx264 @ 0x7ffb89809200] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 AVX2 LZCNT BMI2
[libx264 @ 0x7ffb89809200] profile High, level 3.0
[libx264 @ 0x7ffb89809200] 264 - core 148 r2748 97eaef2 - H.264/MPEG-4 AVC codec - Copyleft 2003-2016 - 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=11 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=25 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
Output #0, mp4, to 'output.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf57.71.100
    Stream #0:0: Audio: aac (LC) ([64][0][0][0] / 0x0040), 44100 Hz, stereo, fltp, 128 kb/s (default)
    Metadata:
      encoder         : Lavc57.89.100 aac
    Stream #0:1(und): Video: h264 (libx264) ([33][0][0][0] / 0x0021), yuv420p, 480x360 [SAR 1:1 DAR 4:3], q=-1--1, 30 fps, 15360 tbn, 30 tbc (default)
    Metadata:
      handler_name    : VideoHandler
      encoder         : Lavc57.89.100 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
Error marking filters as finished
[aac @ 0x7ffb89803e00] Qavg: 396.836
[aac @ 0x7ffb89803e00] 2 frames left in the queue on closing
[libx264 @ 0x7ffb89809200] frame I:1     Avg QP:21.53  size:  7477
[libx264 @ 0x7ffb89809200] frame P:12    Avg QP:23.25  size:  2910
[libx264 @ 0x7ffb89809200] frame B:25    Avg QP:23.89  size:   465
[libx264 @ 0x7ffb89809200] consecutive B-frames:  2.4% 19.5%  0.0% 78.0%
[libx264 @ 0x7ffb89809200] mb I  I16..4:  8.6% 80.1% 11.3%
[libx264 @ 0x7ffb89809200] mb P  I16..4:  2.8% 20.3%  2.7%  P16..4: 48.5% 10.2%  1.9%  0.0%  0.0%    skip:13.6%
[libx264 @ 0x7ffb89809200] mb B  I16..4:  0.2%  1.7%  0.4%  B16..8: 21.1%  1.5%  0.1%  direct: 0.3%  skip:74.7%  L0:38.5% L1:59.3% BI: 2.2%
[libx264 @ 0x7ffb89809200] 8x8 transform intra:78.3% inter:85.8%
[libx264 @ 0x7ffb89809200] coded y,uvDC,uvAC intra: 60.5% 71.8% 8.2% inter: 6.5% 13.4% 0.1%
[libx264 @ 0x7ffb89809200] i16 v,h,dc,p: 17% 22% 11% 49%
[libx264 @ 0x7ffb89809200] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 21% 22% 12%  7%  7%  6%  9%  8%  8%
[libx264 @ 0x7ffb89809200] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 25% 23% 11%  4% 11%  8% 10%  5%  3%
[libx264 @ 0x7ffb89809200] i8c dc,h,v,p: 45% 25% 20% 10%
[libx264 @ 0x7ffb89809200] Weighted P-Frames: Y:0.0% UV:0.0%
[libx264 @ 0x7ffb89809200] ref P L0: 85.1%  4.3%  8.4%  2.3%
[libx264 @ 0x7ffb89809200] ref B L0: 93.7%  4.7%  1.6%
[libx264 @ 0x7ffb89809200] ref B L1: 99.0%  1.0%
[libx264 @ 0x7ffb89809200] kb/s:341.28
Conversion failed!