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• Ffmpeg makes audio longer when changing bitrate

  17 mars 2020, par ReflexLevel0

  I’ve been using ffmpeg convert audio from one format to another and to change audio’s bitrate. When I try to convert aac audio to mp3 audio using the command :

  ffmpeg -i SomeAudio.aac -c:a mp3 -b:a 128k SomeOutputPath.mp3

  everything works correctly and output audio is of the same length as the input audio (6 minutes, 15 seconds).

  However, when I try converting it to aac audio using a similar command :

  ffmpeg -i SomeAudio.aac -c:a aac -b:a 128k SomeOutputPath.aac

  it makes the output audio longer (around 10 minutes). I have tried specifying output length but that still makes the video longer, it just cuts of part of the audio :

  ffmpeg -i SomeAudio.aac -c:a aac -b:a 128k -t 00:06:15 SomeOutputPath.aac

  Here is a link to the screenshot :

  

  My suspicion is that message "Estimating duration from bitrate, this may be innacurate" (the one in the screenshot) is the root of my problem but I just haven’t been able to find any useful information about it on the web.

  Thanks a lot for any help in advance :)

• Add multiple audio files to video at specific points using FFMPEG

  7 août 2012, par Pascal Beyeler

  I am trying to create a video out of a sequence of images and various audio files using FFmpeg. While it is no problem to create a video containing the sequence of images with the following command :

  ffmpeg -f image2 -i image%d.jpg video.mpg

  I haven't found a way yet to add audio files at specific points to the generated video.
  Is it possible to do something like :

  ffmpeg -f image2 -i image%d.jpg -i audio1.mp3 AT 10s -i audio2.mp3 AT 15s video.mpg

  Any help is much appreciated !

  EDIT :

  The solution in my case was to use sox as suggested by blahdiblah in the answer below. You first have to create an empty audio file as a starting point like that :

  sox -n -r 44100 -c 2 silence.wav trim 0.0 20.0

  This generates a 20 sec empty WAV file. After that you can mix the empty file with other audio files.

  sox -m silence.wav "|sox sound1.mp3 -p pad 0" "|sox sound2.mp3 -p pad 2" out.wav

  The final audio file has a duration of 20 seconds and plays sound1.mp3 right at the beginning and sound2.mp3 after 2 seconds.
  To combine the sequence of images with the audio file we can use FFmpeg.

  ffmpeg -i video_%05d.png -i out.wav -r 25 out.mp4

• Add multiple audio files to video at specific points using FFMPEG

  20 juillet 2023, par Pascal

  I am trying to create a video out of a sequence of images and various audio files using FFmpeg. While it is no problem to create a video containing the sequence of images with the following command :

  



  ffmpeg -f image2 -i image%d.jpg video.mpg


  



  I haven't found a way yet to add audio files at specific points to the generated video. 
Is it possible to do something like :

  



  ffmpeg -f image2 -i image%d.jpg -i audio1.mp3 AT 10s -i audio2.mp3 AT 15s video.mpg


  



  Any help is much appreciated !

  



  EDIT :

  



  The solution in my case was to use sox as suggested by blahdiblah in the answer below. You first have to create an empty audio file as a starting point like that :

  



  sox -n -r 44100 -c 2 silence.wav trim 0.0 20.0


  



  This generates a 20 sec empty WAV file. After that you can mix the empty file with other audio files.

  



  sox -m silence.wav "|sox sound1.mp3 -p pad 0" "|sox sound2.mp3 -p pad 2" out.wav


  



  The final audio file has a duration of 20 seconds and plays sound1.mp3 right at the beginning and sound2.mp3 after 2 seconds.
To combine the sequence of images with the audio file we can use FFmpeg.

  



  ffmpeg -i video_%05d.png -i out.wav -r 25 out.mp4