FFmpeg concatenates two m4a files incorrectly

Question

Problem is, when i concatenate two m4a files with concat demuxer, ffmpeg produces files whose duration is incorrect. You can see that the duration of output file is very different from the duration of two input files combined. Please help me spot the issue in it. My ultimate goal is to append silent audio to the end of the audio file. For that, i generate silent audio file with ffmpeg and then try to concat it with other audio file.

Command I used to generate audio file:

ffmpeg -nostdin -loglevel error -y -threads 0 -filter_complex aevalsrc=0 -t 4 /home/ec2-user/videocreation/temp/silence.m4a

Command I used for concat:

ffmpeg -f concat -safe 0 -i temp.txt -c copy output.m4a

I have two file paths listed in temp.txt:

[ec2-user@ip-10-0-1-126 server]$ cat temp.txt 
file /home/ec2-user/videoData/DnXptC4ld8/FADING_OUT_VOLUP_Blrt_Decrypt_1ed5c4d569d8a1f23428b65217f65eaf_audio.m4a
file /home/ec2-user/videocreation/temp/silence.m4a

First file ffprobe:

[ec2-user@ip-10-0-1-126 server]$ ffprobe /home/ec2-user/videoData/DnXptC4ld8/FADING_OUT_VOLUP_Blrt_Decrypt_1ed5c4d569d8a1f23428b65217f65eaf_audio.m4a 
ffprobe version N-80097-g89e9393 Copyright (c) 2007-2016 the FFmpeg developers
  built with gcc 4.8.5 (GCC) 20150623 (Red Hat 4.8.5-4)
  configuration: --prefix=/home/ec2-user/ffmpeg_build --extra-cflags=-I/home/ec2-user/ffmpeg_build/include --extra-ldflags=-L/home/ec2-user/ffmpeg_build/lib --bindir=/home/ec2-user/bin --pkg-config-flags=--static --enable-gpl --enable-nonfree --enable-libfdk-aac --enable-libfreetype --enable-libmp3lame --enable-libopus --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265
  libavutil      55. 24.100 / 55. 24.100
  libavcodec     57. 43.100 / 57. 43.100
  libavformat    57. 37.100 / 57. 37.100
  libavdevice    57.  0.101 / 57.  0.101
  libavfilter     6. 46.100 /  6. 46.100
  libswscale      4.  1.100 /  4.  1.100
  libswresample   2.  0.101 /  2.  0.101
  libpostproc    54.  0.100 / 54.  0.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/home/ec2-user/videoData/DnXptC4ld8/FADING_OUT_VOLUP_Blrt_Decrypt_1ed5c4d569d8a1f23428b65217f65eaf_audio.m4a':
  Metadata:
    major_brand     : M4A 
    minor_version   : 512
    compatible_brands: isomiso2
    encoder         : Lavf57.44.100
  Duration: 00:00:01.77, start: 0.000000, bitrate: 4 kb/s
    Stream #0:0(und): Audio: aac (LC) (mp4a / 0x6134706D), 11025 Hz, mono, fltp, 0 kb/s (default)
    Metadata:
      handler_name    : SoundHandler

Second file ffprobe:

[ec2-user@ip-10-0-1-126 server]$ ffprobe /home/ec2-user/videocreation/temp/silence.m4a
ffprobe version N-80097-g89e9393 Copyright (c) 2007-2016 the FFmpeg developers
  built with gcc 4.8.5 (GCC) 20150623 (Red Hat 4.8.5-4)
  configuration: --prefix=/home/ec2-user/ffmpeg_build --extra-cflags=-I/home/ec2-user/ffmpeg_build/include --extra-ldflags=-L/home/ec2-user/ffmpeg_build/lib --bindir=/home/ec2-user/bin --pkg-config-flags=--static --enable-gpl --enable-nonfree --enable-libfdk-aac --enable-libfreetype --enable-libmp3lame --enable-libopus --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265
  libavutil      55. 24.100 / 55. 24.100
  libavcodec     57. 43.100 / 57. 43.100
  libavformat    57. 37.100 / 57. 37.100
  libavdevice    57.  0.101 / 57.  0.101
  libavfilter     6. 46.100 /  6. 46.100
  libswscale      4.  1.100 /  4.  1.100
  libswresample   2.  0.101 /  2.  0.101
  libpostproc    54.  0.100 / 54.  0.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/home/ec2-user/videocreation/temp/silence.m4a':
  Metadata:
    major_brand     : M4A 
    minor_version   : 512
    compatible_brands: isomiso2
    encoder         : Lavf57.44.100
  Duration: 00:00:04.02, start: 0.000000, bitrate: 4 kb/s
    Stream #0:0(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, mono, fltp, 1 kb/s (default)
    Metadata:
      handler_name    : SoundHandler

Output file ffprobe:

[ec2-user@ip-10-0-1-126 server]$ ffprobe output.m4a 
ffprobe version N-80097-g89e9393 Copyright (c) 2007-2016 the FFmpeg developers
  built with gcc 4.8.5 (GCC) 20150623 (Red Hat 4.8.5-4)
  configuration: --prefix=/home/ec2-user/ffmpeg_build --extra-cflags=-I/home/ec2-user/ffmpeg_build/include --extra-ldflags=-L/home/ec2-user/ffmpeg_build/lib --bindir=/home/ec2-user/bin --pkg-config-flags=--static --enable-gpl --enable-nonfree --enable-libfdk-aac --enable-libfreetype --enable-libmp3lame --enable-libopus --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265
  libavutil      55. 24.100 / 55. 24.100
  libavcodec     57. 43.100 / 57. 43.100
  libavformat    57. 37.100 / 57. 37.100
  libavdevice    57.  0.101 / 57.  0.101
  libavfilter     6. 46.100 /  6. 46.100
  libswscale      4.  1.100 /  4.  1.100
  libswresample   2.  0.101 /  2.  0.101
  libpostproc    54.  0.100 / 54.  0.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'output.m4a':
  Metadata:
    major_brand     : M4A 
    minor_version   : 512
    compatible_brands: isomiso2
    encoder         : Lavf57.37.100
  Duration: 00:00:23.22, start: 0.000000, bitrate: 0 kb/s
    Stream #0:0(und): Audio: aac (LC) (mp4a / 0x6134706D), 11025 Hz, mono, fltp, 0 kb/s (default)
    Metadata:
      handler_name    : SoundHandler

score 0 · Accepted Answer · answered Feb 26 '17 at 07:12

0

Files need to have the same properties. Your silence file has a different sampling rate. Use

ffmpeg -f lavfi -i anullsrc -ar 11025 -ac 1 -t 4 silence.m4a

answered Feb 26 '17 at 07:12

Gyan

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@asad Doesn't make a difference, but alternatively you can use `anullsrc=r=11025:cl=mono` and omit `-ar` & `-ac`. – llogan Feb 26 '17 at 07:57

FFmpeg concatenates two m4a files incorrectly

1 Answers1