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• preserve alpha channel when changing resolution in webm vp9 ffmpeg

  28 juin 2022, par Patrick Vellia

  I am running the streamio-ffmpeg gem in my Ruby code here to operate the FFMPEG command.

  


  Setting a Webm with codec VP9 that has alpha transparent frames in it as the input, I want to change the resolution from 1080p to 720p and preserve the alpha transparent frames when outputting to the same format/codec.

  


  I've tried it several different ways, but every time it outputs with a black background where the alpha transparent background should be, but ffprobe shows that ALPHA_MODE is set to 1.

  


  Here's the command that streamio-ffmpeg tells the system :

  


  ["/usr/local/bin/ffmpeg", "-y", "-i", "part1.webm", "-s", "1920x1080", "-aspect", "1.7777777777777777", "videos/movie_transparent_1920x1080.webm"]


  


  This one should have been exactly the same as the original, since the original resolution WAS 1080p. The resulting file is actually black background instead of transparent.

  


  Here's my Ruby code :

  


  def process_alpha_transparency(output)
    render_res = []
    case @height
    when 1080..2160
        render_res.append("1920x1080", "1280x720", "852x480")
    when 720..1079
        render_res.append("1280x720", "852x480")
    when 480..719
        render_res.append("852x480")
    when 0..479
        render_res.append(@resolution)
    end

    formats = ["webm", "mov"]
    combined_time_start = Time.now

    render_res.each do |res|
        formats.each do |format|
            puts "Rendering a #{res} resolution version."
            if format == "webm"
                options = {
                    resolution: res 
                }

                time_start = Time.now
                @movie.transcode("videos/#{output}_transparent_#{res}.#{format}", options)
                time_elapsed = Time.now - time_start

                puts "Te resolution rendering completed in #{time_elapsed.to_i.to_s} seconds."
            end
        end
    end

    combined_elapsed_time = Time.now - combined_time_start
    puts "The process completed in #{combined_elapsed_time.to_i.to_s} seconds."

    
end


  


• Merging/concatenating video and keeping sound in R using AV package

  30 juin 2022, par Jack Cornwall

  I am trying to merge/concatenate multiple videos with sound sequentially into one video using only R, (I don't want to work with ffmpeg in the command line as the rest of the project doesn't require it and I would rather not bring it in at this stage).

  


  My code looks like the following :

  


  dir<-"C:/Users/Admin/Documents/r_programs/"

videos<-c(
  paste0(dir,"video_1.mp4"),
  paste0(dir,"video_2.mp4"),
  paste0(dir,"video_3.mp4")
)

#encoding
av_encode_video(
  videos,
  output=paste0(dir,"output.mp4"),
  framerate=30,
  vfilter="null",
  codec="libx264rgb",
  audio=videos,
  verbose=TRUE
)


  


  It almost works, the output file is an mp4 containing the 3 videos sequentially one after the other, but the audio present is only from the first of the 3 video and then it cuts off.

  


  It doesn't really matter what the videos are. I have recreated this issue with the videos I was using or even 3 randomly downloaded 1080p 30fps videos from YouTube.

  


  Any help is appreciated & thank you in advance.

  


• FFMPEG scaling video disable viewing it while process is not ended, for video transcoding on the fly

  5 juillet 2022, par Lucas F

  Good day all,

  


  I'm working on a video player with 1080p original video files, and I would like to change their resolution on the fly :

  


  Actually I host all my original video files under a web mp4 1080p format, and I would like to be able to offer 720p, 480p, etc ... qualities.

  


  So I started to look for tutorials about video transcoding on the fly and I found the FFMPEG tool.

  


  I'm actually using the following command to scale videos - to 720p for e.g. :

  


  ffmpeg -i input.mp4 -vf scale=-1:720 output.mp4


  


  The problem is, once FFMPEG starts scaling it, I have to wait the end of the process before being able to play the video. Do you know if there is any parameter for this command to allow playing the video while it's under scaling ?

  


  Or any workaround that can help me doing this ?

  


  Thank you in advance for your help !

  


  EDIT

  


  Now I found how to access readable content while transcoding (by transcoding to fragmented MP4) :

  


  ffmpeg -i input.mp4 -vf scale=-2:720 -movflags +frag_keyframe+separate_moof+omit_tfhd_offset+empty_moov output.mp4


  


  But my problem is when opening the video it comes as an "ended" video of the current transcoded data.

  


  So if video lasts 1min and is half transcoded, I'll see only 30s, it will not load more data, once the rest is transcoded.