ajuste de audio ffmpeg mp4

Mi mp4 es h264 + aac Quiero usar ffmpeg.exe para agregarle una música de fondo, esta musci es más corta que la mp4, por lo tanto, la música debería repetirse

Yo he tratado ffmpeg -i test.mp4 -i background.m4a -filter_complex "amovie=background.m4a:loop=0" output.mp4

pero obtengo un mal resultado, reemplaza la pista de audio de mi test.mp4 por background.m4a no se mezcla ¿Podría alguien dar alguna ayuda?

actualizar

G:\bin>ffmpeg -i test.mp4 -filter_complex "amovie=music.m4a:loop=0[loop],volume=0.5;[0:a][loop]amerge=inputs=2[a]"  -map 0:v -map "[a]
" -c:v copy -ac 2 -shortest -movflags +faststart output.mp4
ffmpeg version N-66931-gbbd8c85 Copyright (c) 2000-2014 the FFmpeg developers
  built on Oct 17 2014 01:09:43 with gcc 4.9.1 (GCC)
  configuration: --disable-static --enable-shared --enable-gpl --enable-version3 --disable-w32threads --enable-avisynth --enable-bzlib --enable-fontco
nfig --enable-frei0r --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libfreetype --enable
-libgme --enable-libgsm --enable-libilbc --enable-libmodplug --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libope
njpeg --enable-libopus --enable-librtmp --enable-libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --enable-li
bvidstab --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enab
le-libx265 --enable-libxavs --enable-libxvid --enable-zlib
  libavutil      54. 10.100 / 54. 10.100
  libavcodec     56.  8.100 / 56.  8.100
  libavformat    56.  9.100 / 56.  9.100
  libavdevice    56.  1.100 / 56.  1.100
  libavfilter     5.  1.106 /  5.  1.106
  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 'test.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf56.15.102
  Duration: 00:02:00.04, start: 0.000000, bitrate: 2947 kb/s
    Stream #0:0(und): Video: h264 (Constrained Baseline) (avc1 / 0x31637661), yuv420p, 1280x720, 2846 kb/s, 15.97 fps, 25000000.00 tbr, 25000000.00 tb
n, 50000000.00 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 96 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
File 'output.mp4' already exists. Overwrite ? [y/N] y
[Parsed_amerge_2 @ 0000000000302880] No channel layout for input 1
[Parsed_amerge_2 @ 0000000000302880] Input channel layouts overlap: output layout will be determined by the number of distinct input channels
Output #0, mp4, to 'output.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf56.9.100
    Stream #0:0: Audio: aac (libvo_aacenc) ([64][0][0][0] / 0x0040), 44100 Hz, stereo, s16, 128 kb/s
    Metadata:
      encoder         : Lavc56.8.100 libvo_aacenc
    Stream #0:1(und): Video: h264 ([33][0][0][0] / 0x0021), yuv420p, 1280x720, q=2-31, 2846 kb/s, 15.97 fps, 25000000.00 tbn, 25000000.00 tbc (default
)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:2: Audio: aac (libvo_aacenc) ([64][0][0][0] / 0x0040), 44100 Hz, stereo, s16, 128 kb/s
    Metadata:
      encoder         : Lavc56.8.100 libvo_aacenc
Stream mapping:
  Stream #0:1 (aac) -> volume
  Stream #0:1 (aac) -> amerge:in0
  volume -> Stream #0:0 (libvo_aacenc)
  Stream #0:0 -> #0:1 (copy)
  amerge -> Stream #0:2 (libvo_aacenc)
Press [q] to stop, [?] for help
[mp4 @ 00000000003044c0] Starting second pass: moving the moov atom to the beginning of the file
frame= 1917 fps=382 q=-1.0 Lsize=   45571kB time=00:02:00.00 bitrate=3110.9kbits/s
video:41707kB audio:3751kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.248006%

Actualización2:

➜  misc  ffmpeg -i test.mp4 -filter_complex "amovie=music.m4a:loop=1[loop];[0:a][loop]amerge=inputs=2[a]" -map 0:v -map "[a]" -c:v copy -ac 2  -movflags +faststart -strict -2 output.mp4
ffmpeg version 2.6.2 Copyright (c) 2000-2015 the FFmpeg developers
  built with llvm-gcc 4.2.1 (LLVM build 2336.11.00)
  configuration: --prefix=/Volumes/Ramdisk/sw --enable-gpl --enable-pthreads --enable-version3 --enable-libspeex --enable-libvpx --disable-decoder=libvpx --enable-libmp3lame --enable-libtheora --enable-libvorbis --enable-libx264 --enable-avfilter --enable-libopencore_amrwb --enable-libopencore_amrnb --enable-filters --enable-libgsm --enable-libvidstab --enable-libx265 --disable-doc --arch=x86_64 --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
  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 'test.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf56.15.102
  Duration: 00:02:52.52, start: 0.000000, bitrate: 2867 kb/s
    Stream #0:0(und): Video: h264 (Constrained Baseline) (avc1 / 0x31637661), yuv420p, 1280x720, 2765 kb/s, 17.11 fps, 25000k tbr, 25000k tbn, 50000k tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 96 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
File 'output.mp4' already exists. Overwrite ? [y/N] y
[Parsed_amerge_1 @ 0x7f804bd0f880] No channel layout for input 1
[Parsed_amerge_1 @ 0x7f804bd0f880] Input channel layouts overlap: output layout will be determined by the number of distinct input channels
Output #0, mp4, to 'output.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf56.25.101
    Stream #0:0(und): Video: h264 ([33][0][0][0] / 0x0021), yuv420p, 1280x720, q=2-31, 2765 kb/s, 17.11 fps, 25000k tbr, 25000k tbn, 25000k tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1: Audio: aac ([64][0][0][0] / 0x0040), 44100 Hz, stereo, fltp, 128 kb/s (default)
    Metadata:
      encoder         : Lavc56.26.100 aac
Stream mapping:
  Stream #0:1 (aac) -> amerge:in0
  Stream #0:0 -> #0:0 (copy)
  amerge -> Stream #0:1 (aac)
Press [q] to stop, [?] for help
Error while decoding stream #0:1: Cannot allocate memory
    Last message repeated 6517 times
frame= 2663 fps=0.0 q=-1.0 size=   49484kB time=00:02:35.84 bitrate=2601.2kbits/Error while decoding stream #0:1: Cannot allocate memory
    Last message repeated 715 times
[mp4 @ 0x7f804c05b000] Starting second pass: moving the moov atom to the beginning of the file
frame= 2952 fps=0.0 q=-1.0 Lsize=   58332kB time=00:02:52.47 bitrate=2770.5kbits/s    
video:58245kB audio:49kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.065551%
➜  misc 

Debe fusionar ambas entradas en una sola secuencia con amerge. Esto creará una transmisión de audio de 4 canales (suponiendo que ambas entradas sean estéreo) que luego se volverá a mezclar en estéreo -ac 2.

ffmpeg -i video.mp4 -filter_complex \
"amovie=music.m4a:loop=0[loop]; \
 [0:a][loop]amerge=inputs=2[a]" \
-map 0:v -map "[a]" -c:v copy -ac 2 -shortest -movflags +faststart output.mp4

• -shortestse usa aquí para evitar que se codifique para siempre, ya que se amovierepetirá infinitamente.

• Si desea reducir el volumen de la música, use el volumefiltro.

• No proporcionó información sobre sus entradas, por lo que asumí que ambas entradas contienen audio estéreo.

• El video se copia en secuencia para evitar una nueva codificación innecesaria.