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• syncing video thumbnail frames with source video

  12 octobre 2020, par bigless

  We are trying to make video preview for seek bar. One approach is to make tons of images like Youtube does. We chose second one - 160x90(*) preview video without sound with fps limited to max 4 (250ms, based on duration) - one file with native seek sounds good to me.

  


  This is current cmd we use :

  


  ffmpeg -y -i $source$ -vf scale=$width$:$height$ -an -sn -r $fps$ -vcodec libx264 -x264-params keyint=$keyframe_interval$:scenecut=0  


  


  The idea is that browser is able to fetch whole video preview (<10MB) so there is priority to minimize the size. It seems that html5 video player is able to seek to and decode other than keyframes so we set keyframe interval to duration of video with limit of max 384(1920/5px) for best compression ratio.

  &#xA;

  The issue we are facing is frame sync. When I hover seek bar, video preview shows frame that actually lacks 1-2sec behind hovered time. Does anyone got explanation and possibly fix for this ? Is there some time deviation when player decodes frame instead of showing keyframe ?

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• Video upload with carrierwave-video on Rails 4

  15 juin 2017, par MJRLGUE

  it’s been a while I am fighting to play a video in my rails app.

  I am using carrierwave-video, OS : Windows 10 64bits, to stream/show a video in user posts.

  Here is what I did :

  the file video_uploader.rb :

  class VideoUploader < CarrierWave::Uploader::Base
  
  
  
    include CarrierWave::Video
  
    storage :file
  
    def store_dir
  
      "uploads/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
  
    end
  
  end

  in the file : _post.html.erb :

  with this line of code : <%= video_tag post.video_url :controls =>true %> I get a blank box with the size of the video.
  and I tried this too and still doesn’t work : <%= video_tag post.video.url if post.video? %>

  I tried ffmpeg too, I installed ffmpeg in my pc and I did include : process encode_video: [:mp4, callbacks: { after_transcode: :set_success } ] in video_uploader.rb file and I get this form error message :

  Video Failed to transcode with FFmpeg. Check ffmpeg install and verify
  video is not corrupt or cut short. Original error : ArgumentError

  Any suggestions please ?

• ffmpeg4android : overlay a video on video with opacity

  21 juin 2016, par LuongTruong

  I am using ffmpeg4android to edit video. Now, I am able to overlay a video on a video by using this command :

  String[] complexCommand = {"ffmpeg","-y" ,"-i", "/sdcard/videokit/in_big.mp4","-strict","experimental", "-vf", "movie=/sdcard/videokit/in_small.mp4 [watermark]; [in][watermark] overlay=main_w-overlay_w-0:0 [out]","-s", "320x240","-r", "30", "-b", "15496k", "-vcodec", "mpeg4","-ab", "48000", "-ac", "2", "-ar", "22050", "/sdcard/videokit/out.mp4"};

  Now, I want to change the opacity of the video "in_small.mp4" which will be on the top of another video.

  Some useful links :
  using ffmpeg to add overlay with opacity
  ffmpeg overlay video with semi transparent video
  

  From those links, I know that all_opacity should be the keyword in this case, but I do not know where to put it in the command.

  Please let me know if you have any ideas. Any suggestion would be appreciated !