Title: Separate or merge audio and video using ffmpeg
       Author: Solène
       Date: 20 December 2019
       Tags: ffmpeg
       Description: 
       
       # Extract audio and video (separation)
       
       If for some reasons you want to separate the audio and the video from a
       file
       you can use those commands:
       
           ffmpeg -i input_file.flv -vn -acodec copy audio.aac
       
           ffmpeg -i input_file.flv -an -vcodec copy video.mp4
       
       Short explanation:
       
       - `-vn` means `-video null` and so you discard video
       - `-an` means `-audio null` and so you discard audio
       - `codec copy` means the output is using original format from the file.
       If the
         audio is mp3 then the output file will be a mp3 whatever the
       extension you
         choose.
       
       Instead of using codec copy you can choose a different codec for the
       extracted
       file, but copy is a good choice, it performs really fast because you
       don't need
       to re-encode it and is loss-less.
       
       I use this to rework the audio with audacity.
       
       
       # Merge audio and video into a single file (merge)
       
       After you reworked tracks (audio and/or video) of your file, you can
       combine
       them into a single file.
       
           ffmpeg -i input_audio.aac -i input_video.mp4 -acodec copy -vcodec
       copy -f flv merged_video.flv