FFMpeg - add background music

Question

here is what i have: input1.avi - video that contain sounds. input2.avi - video that doesn't contain sounds. music.mp3 - audio file.

i want to add background music(music.mp3 file) to the video.

C:\input1.avi -i C:\music.mp3 -shortest -c:v copy -c:a copy C:\output1.avi

then output1.avi is the same as input1 - movie with sounds but without the background music (music.mp3)

when i try to use the other file (video without sounds):

C:\input2.avi -i C:\music.mp3 -shortest -c:v copy -c:a copy C:\output2.avi

then output2.avi is the same as input2 + it have the background music.

so why input1 does not contain the background music??? and how can i decrease or increase the volume of music.mp3 file?

thanks.

---

console output:

C:\motionbee\ffmpeg\bin>ffmpeg -i C:\input.avi
-i C:\music.mp3 -shortest -c:v copy -filter_
complex "[0:a]aformat=fltp:44100:stereo[0a];[1]aformat=fltp:44100:stereo,volume=
1.5[1a];[0a][1a]amix[a]" -map 0:v -map "[a]" -ac 2 C:\output1.avi
ffmpeg version N-78949-g6f5048f Copyright (c) 2000-2016 the FFmpeg developers
  built with gcc 5.3.0 (GCC)
  configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-av
isynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enab
le-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --
enable-libdcadec --enable-libfreetype --enable-libgme --enable-libgsm --enable-l
ibilbc --enable-libmodplug --enable-libmfx --enable-libmp3lame --enable-libopenc
ore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --ena
ble-librtmp --enable-libschroedinger --enable-libsoxr --enable-libspeex --enable
-libtheora --enable-libtwolame --enable-libvidstab --enable-libvo-amrwbenc --ena
ble-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx
264 --enable-libx265 --enable-libxavs --enable-libxvid --enable-libzimg --enable
-lzma --enable-decklink --enable-zlib
  libavutil      55. 19.100 / 55. 19.100
  libavcodec     57. 27.101 / 57. 27.101
  libavformat    57. 28.100 / 57. 28.100
  libavdevice    57.  0.101 / 57.  0.101
  libavfilter     6. 39.100 /  6. 39.100
  libswscale      4.  0.100 /  4.  0.100
  libswresample   2.  0.101 /  2.  0.101
  libpostproc    54.  0.100 / 54.  0.100
Input #0, avi, from 'C:\input.avi':
  Metadata:
    encoder         : Lavf57.28.100
  Duration: 00:02:05.76, start: 0.000000, bitrate: 450 kb/s
    Stream #0:0: Video: mpeg4 (Simple Profile) (XVID / 0x44495658), yuv420p, 720
x480 [SAR 1:1 DAR 3:2], 440 kb/s, 25 fps, 25 tbr, 25 tbn, 25 tbc
    Stream #0:1: Audio: mp3 (U[0][0][0] / 0x0055), 44100 Hz, stereo, s16p, 128 k
b/s
[mp3 @ 00000000005c8020] Skipping 0 bytes of junk at 32370.
Input #1, mp3, from 'C:\music.mp3':
  Metadata:
    title           : Broadcast News Package - News Intro
    artist          : After Effects News Template
  Duration: 00:01:57.89, start: 0.025057, bitrate: 194 kb/s
    Stream #1:0: Audio: mp3, 44100 Hz, stereo, s16p, 192 kb/s
    Metadata:
      encoder         : Lavc56.26
File 'C:\output1.avi' already exists. Overwrite
? [y/N] y
Output #0, avi, to 'C:\output1.avi':
  Metadata:
    ISFT            : Lavf57.28.100
    Stream #0:0: Video: mpeg4 (XVID / 0x44495658), yuv420p, 720x480 [SAR 1:1 DAR
 3:2], q=2-31, 440 kb/s, 25 fps, 25 tbr, 25 tbn, 25 tbc
    Stream #0:1: Audio: mp3 (libmp3lame) (U[0][0][0] / 0x0055), 44100 Hz, stereo
, fltp (default)
    Metadata:
      encoder         : Lavc57.27.101 libmp3lame
Stream mapping:
  Stream #0:1 (mp3) -> aformat
  Stream #1:0 (mp3) -> aformat
  Stream #0:0 -> #0:0 (copy)
  amix -> Stream #0:1 (libmp3lame)
Press [q] to stop, [?] for help
frame= 3118 fps=0.0 q=-1.0 Lsize=    6917kB time=00:02:05.76 bitrate= 450.6kbits
/s speed= 867x
video:6754kB audio:74kB subtitle:0kB other streams:0kB global headers:0kB muxing
 overhead: 1.307944%

Answer 1

When multiple streams are available, and no map is specified, ffmpeg picks one video and one audio stream from among the inputs.

Since you will likely need to re-encode audio, you can use

ffmpeg -i C:\input1.avi -i C:\music.mp3 -c:v copy \
       -filter_complex "[0:a]aformat=fltp:44100:stereo,apad[0a];[1]aformat=fltp:44100:stereo,volume=1.5[1a];[0a][1a]amerge[a]" \
       -map 0:v -map "[a]" -ac 2 C:\output1.avi

Answer 2

I tried this command seems to be working.

ffmpeg -i audio.mp3 -i input.mp4 -filter_complex "[0:a][1:a]amerge,pan=stereo|c0<c0+c2|c1<c1+c3[out]" -map 1:v -map "[out]" -c:v copy -shortest output.mp4

Things changed :

1. Unknown encoder 'libfdk_aac'
2. This syntax is deprecated. Use '|' to separate the list items ('stereo|c0<c0+c2|c1<c1+c3' instead of 'stereo|c0<c0+c2:c1<c1+c3')