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• Rails generate dynamic ffmpeg command

  13 janvier 2024, par Seto

  I'm trying to combine several videos into one with ffmpeg command called from a Ruby script in a Rails ActionJob class. The number of input videos is unlimited. This is how I did it right now.

  


   def perform(project_id)
    @project = Project.find(project_id)
    logger.info 'ProjectGenerateVlogJob#perform'
    logger.debug "project: #{@project.inspect}"
    setup_directory

    result_filename = "#{@project.id}-vlog.mp4"
    execute_command = <<-FFMPEG
      find *.mp4 | sed 's:\ :\\\ :g'| sed 's/^/file /' > fl.txt; ffmpeg -f concat -i fl.txt -c copy #{result_filename}; rm fl.txt
    FFMPEG

    logger.debug "ffmpeg_command: #{execute_command}"
    `#{execute_command}`
  end


  


  But that command is not stable, in a way that the generated video has problems, namely un-synch audio, video gets cut off, etc.

  


  This is how I did it through the console manually that produced the best result so far :

  


  $ ffmpeg -i IMG_1-same.MOV -i IMG_2-same.MOV -i IMG_3-same.MOV \
-filter_complex "[0:v] [0:a] [1:v] [1:a] [2:v] [2:a] \
concat=n=3:v=1:a=1 [v] [a]" \
-map "[v]" -map "[a]" -vsync vfr vlog-1.mp4


  


  The thing is, I don't know how to generate the command dynamically so it can be run by the Ruby script. Any pointers ?

  


  The Project model has many videos, and when I looped through it it produced multiple lines of command and it's not a valid command when I run it from Ruby.

  


• Mapping streams by language in FFmpeg

  8 décembre 2016, par ffmpeg123

  I have lots of files with multiple audio and subtitle languages, however the track numbers aren’t consistent (the English audio stream isn’t always the first) so using a command such as :

  ffmpeg -i "input.mkv" -map 0 -map -0:a:1 -c:v copy -c:a copy "output.mkv"

  doesn’t yield expected results. After searching around I discovered it was possible to map streams based on language with this command :

  ffmpeg -i "input.mkv" -map 0 -map -0:m:language:eng -c:v copy -c:a copy "output.mkv"

  However -map -0:m:language:eng will remove all tracks with the English language flag. To keep the subtitle tracks you can use -map 0:s this is a good solution however, I want to know if it’s possible to only map audio streams based on language.

• How to extract track 2 left channel using ffmpeg ?

  1er mai 2019, par flash

  I am working on a mp4 file in which I want to extract Track 2 left channel using ffmpeg.

  

  I tried with the following command on terminal but it seems to extract Track 1 - [English] :

  ffmpeg -i 36017P.mp4 filename.mp3

  Problem Statement :

  I am wondering what changes I need to make in the ffmpeg command above so that it extract Track 2 -[English] from mp4 file.