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• Extracting image frames from mjpeg given 'frame byte offset' and 'frame size' [on hold]

  2 septembre 2015, par Sonia

  I’m looking for code or pointers to funtions or library that I can use to extract image frames from motion jpeg file. In my case, for each image frame, I know the starting byte offset and the size of the frame (size is not always equal for each frame). Given these data, how can I extract each image frames from mjpeg file.

  I have checked the OpenCV library, I can’t find the detail about giving these two inputs to extract frames. Also, I can’t find it in FFmpeg as well. But, I’m not an expert in these two. I hope anyone could give me pointers to this. It can be just a tool or sourcecode (I use C/C++ and MATLAB but I’m open to other language - just to learn how to do it)

  Thank you very much.

• ruby on rails carrierwave-video ffmpeg AWS

  11 mars 2015, par Joseph Han Nim Jang

  I am trying to create an academic site where users can upload lecture videos and other users can view them - similar to a site like Udemy.

  I am using Carrierwave, Carrierwave-video (for encoding videos), AWS to make this happen. AWS configuration has been done, and it’s working.

  However, I am getting this error. (By the way, I am testing this video feature in a Yelpdemo site, so I am trying to have users upload videos to restaurants for now.)

  rails points the error to @restaurant = Restaurant.new(restaurant_params)

  Errno::ENOENT in RestaurantsController#create

  No such file or directory - ffmpeg

  # POST /restaurants.json
  def create
  @restaurant = Restaurant.new(restaurant_params)

  respond_to do |format|
  
    if @restaurant.save

  This is my video_uploader.rb

  # encoding: utf-8
  
  
  
  class VideoUploader < CarrierWave::Uploader::Base
  
  
  
    include CarrierWave::Video
  
    include CarrierWave::Video::Thumbnailer
  
  
  
    process encode_video: [:mp4]
  
  
  
    include CarrierWave::MiniMagick
  
  
  
    storage :fog
  
  
  
    def store_dir
  
      "uploads/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
  
    end
  
  
  
     version :thumb do
  
        process thumbnail: [{format: 'png', quality: 10, size: 192, strip: true, logger: Rails.logger}]
  
        def full_filename for_file
  
          png_name for_file, version_name
  
        end
  
    end
  
  
  
      def png_name for_file, version_name
  
        %Q{#{version_name}_#{for_file.chomp(File.extname(for_file))}.png}
  
      end
  
  end

  I have manually (added a file to the model) created video.rb in the model - not sure if this is the right way to do it..

  class Video < ActiveRecord::Base
  
  
  
    attr_accessor :user_id, :video,, :type, :filename, :path, :filesize, :width, :height, :duration, :bit_rate
  
  
  
    belongs_to :restaurant
  
    belongs_to :user
  
  
  
    mount_uploader :video, VideoUploader
  
  end

  in app/views/restaurants/show.html.erb for showing the video. Right now, without the encoding done, I can see like an image of the video. When I right lick and copy the code - it gives me the AWS URL which means AWS configuration is in place

          <p>
  
              <strong>Video:</strong>
  
              &lt;%= video_tag @restaurant.video_url %>
  
          </p>

  I am trying to show videos like this.

  I have downloaded FFMPEG (both ffmpeg-2.6 and SnowLeopard_Lion_Mountain_Yosemite_17) - not sure which one’s the right one.. And I have read somewhere that you need to place FFMPEG in your usr/local/bin -> So do you have to physically place ffmpeg exec file in your respective folder ?

  Need your expert help please.

  Thank you in advance !

• How to use qt-faststart in ffmpeg arguments while merging 2 flv files into 1 mp4 format

  21 novembre 2014, par Mohsin Sharpen

  I want to do Pseudo Streaming of an mp4 file generated from 2 different flvs. For that I am using qt-faststart tool in ffmpeg. My generated file is according to my requirement but still Pseudo Streaming is not working.

  Here is my code which is written in Ruby on Rail which merge 2 different flv files and then move them to the final location after generating final mp4 format.

  class VideoProcess < BaseJob
  
  @queue = :video_process
  
  @config_file = 'video_process'
  
  
  
  def self.perform(session_name)
  
      new(session_name).video_merge
  
  end
  
  
  
  def initialize(session_name)
  
      @session_name = session_name
  
      @candidate_file = "#{@session_name}candidate.flv"
  
      @expert_file = "#{@session_name}expert.flv"
  
  
  
      load_config
  
  end
  
  
  
  def video_merge()
  
      left_video = @config[:src_path]+@candidate_file
  
      right_video = @config[:src_path]+@expert_file
  
  
  
      unless File.exists?(left_video)
  
          raise "The file '#{left_video}' does not exist!"
  
      end
  
  
  
      unless File.exists?(right_video)
  
          raise "The file '#{right_video}' does not exist!"
  
      end
  
  
  
      prepare_output_dir @config[:dest_path]
  
  
  
      output_video = "#{@config[:dest_path]}#{@session_name}.#{@config[:output_ext]}"
  
  
  
      filter = generate_filter
  
  
  
      args = strip_spaces %Q|
  
          -i "#{left_video}"
  
          -i "#{right_video}"
  
          -filter_complex "#{filter}"
  
          -map “[left+right]”
  
          -y
  
          -movflags faststart
  
          #{@config[:output_format]}
  
          #{output_video}
  
      |
  
  
  
      command = "#{@config[:command]} #{args} 2>&1" #2>&1 - move error to output
  
  
  
      output = `#{command}`
  
  
  
      puts output
  
  
  
      unless $?.success?
  
          raise output
  
      end
  
  
  
      Resque.enqueue(FileMove, output_video)
  
  
  
      #File.delete left_video, right_video
  
  
  
  end
  
  
  
  def generate_filter
  
      strip_spaces %Q!
  
          nullsrc=size=1040x400 [background];[0:v] setpts=PTS-STARTPTS,
  
          scale=520x400[left];[1:v]setpts=PTS-STARTPTS,scale=520x400[right];
  
          [background][left]overlay=shortest=1[background+left];
  
          [background+left][right]overlay=shortest=1:x=520 [left+right];
  
          [0:1] [1:1] amerge
  
      !
  
  end
  
  
  
  def load_config
  
      super
  
      @config.merge!({
  
          command: @config[:ffmpeg],
  
          padding: @config[:video_w] + @config[:video_space],
  
          overlay: @config[:video_w] * 2 + @config[:video_space]
  
      })
  
  end
  
  # Strip multi spaces to one and remove new line symbol
  
  def strip_spaces(string)
  
      string.gsub("\n",'').gsub(/\s+/, ' ').strip!
  
  end

  end

  Can some one see my code and check if I have set the flag -movflags faststart properly or I need to do something else.

  I am stuck badly as I am not good at ruby on rail/ffmpeg thing.
  Your help will be really appreciated for me in this regard.