FFMpeg Concatenation Filters: Stream specifier ':0' in filtergraph matches no streams

Question

I am developing an application that relies heavily on FFMpeg to perform various transformations on audio files. I am currently testing my FFMpeg configuration on the command line.

I am trying to concatenate multiple audio files which are in different formats (Primarily MP3, MP2 & WAV). I have been using the official TRAC documentation (https://trac.ffmpeg.org/wiki/How%20to%20concatenate%20(join%2C%20merge)%20media%20files#differentcodec) to help me with this and have created the following command:

ffmpeg -i OHIn.wav -i OHOut.wav -filter_complex '[0:0] [1:0] concat=n=2:a=1 [a]' -map '[a]' output.wav

However, when I run this on Mac OS X using version 2.0.1 of FFMpeg, I get the following error message:

Stream specifier ':0' in filtergraph description [0:0] [1:0] concat=n=2:a=1 [a] matches no streams.

Here is my full output from the terminal:

~/ffmpeg -i OHIn.wav -i OHOut.wav -filter_complex '[0:0] [1:0] concat=n=2:a=1 [a]' -map '[a]' output.wav

ffmpeg version 2.0.1 Copyright (c) 2000-2013 the FFmpeg developers
  built on Aug 15 2013 10:56:46 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 --arch=x86_64 --enable-runtime-cpudetect
  libavutil      52. 38.100 / 52. 38.100
  libavcodec     55. 18.102 / 55. 18.102
  libavformat    55. 12.100 / 55. 12.100
  libavdevice    55.  3.100 / 55.  3.100
  libavfilter     3. 79.101 /  3. 79.101
  libswscale      2.  3.100 /  2.  3.100
  libswresample   0. 17.102 /  0. 17.102
  libpostproc    52.  3.100 / 52.  3.100
Guessed Channel Layout for  Input Stream #0.0 : stereo
Input #0, wav, from 'OHIn.wav':
  Duration: 00:00:06.71, bitrate: 1411 kb/s
    Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, stereo, s16, 1411 kb/s
Guessed Channel Layout for  Input Stream #1.0 : stereo
Input #1, wav, from 'OHOut.wav':
  Duration: 00:00:07.19, bitrate: 1411 kb/s
    Stream #1:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, stereo, s16, 1411 kb/s
Stream specifier ':0' in filtergraph description [0:0] [1:0] concat=n=2:a=1 [a] matches no streams.

I do not understand why this does not work. FFMpeg shows that the streams 0:0 and 1:0 exist in the source files. The only other similar problems online have surrounded the use of the single quote in Windows, however testing of this confirm it does not apply to my Mac command line.

Any help would be much appreciated.

Answer 1

You need to tell the concat filter the number of output video streams. The default is v=1 for video and a=0 for audio, but you have no video streams. It's best to not rely on the defaults. Manually list the number of input segments (n), output video streams (v), and output audio streams (a).

ffmpeg -i input0.wav -i input1.wav -filter_complex "[0:a][1:a]concat=n=2:v=0:a=1[a]" -map "[a]" output.wav

Notice that I added v=0.

See the concat filter documentation for more info.

Answer 2

In addition to upvoting Lord Neckbeard's response, which, solved my problem btw: I wanted to provide a working example of a Bash Shell script, showing how I concatenate three mp3 files (an intro, middle and outro, each having the same bitrate of 160 kbps, sample rate of 44.1 Khz) into one result mp3. The reason why my filter graph reads:

[0:a] [1:a] [2:a]

instead of something like:

[0:0] [1:0] [2:0]

is because some mp3s had artwork, which, ffmpeg sees as two streams for each input mp3 file, one audio (for the music itself) and one video (for the image artwork file).

The :a portion lets ffmpeg know that you want it to use only the audio stream(s) that it reads for that input file and to pass that along to the concat filter. So any video filters get ignored. The benefit of doing this is that you don't need to know the position of the video stream (so that you don't accidentally pass it) as specified by running a command like:

ffprobe control-intro-recording.mp3.

Anyways, I digress, here's the shell script:

#!/bin/sh

ffmpeg -i ./source-files/control-intro-recording.mp3 \
-i ./source-files/control-middle-1-hour-recording-with-artwork-160-kbps.mp3 \
-i ./source-files/control-outro-recording.mp3 \
-filter_complex '[0:a] [1:a] [2:a] concat=n=3:v=0:a=1 [a]' \
-map '[a]' ./output-files/control-output-with-artwork-160-kbps-improved.mp3