Replace streamio-ffmpeg library.

Replace the streamio-ffmpeg library with our own very thin FFmpeg wrapper.

app/logical/ffmpeg.rb

@@ -1,4 +1,11 @@
+require "shellwords"
+
+# A wrapper for the ffmpeg command.
 class FFmpeg
+  extend Memoist
+
+  class Error < StandardError; end
+
   attr_reader :file
 
   # Operate on a file with FFmpeg.
@@ -16,10 +23,52 @@ class FFmpeg
 
     # https://ffmpeg.org/ffmpeg.html#Main-options
     # https://ffmpeg.org/ffmpeg-filters.html#thumbnail
-    ffmpeg_out, status = Open3.capture2e("ffmpeg -i #{file.path} -vf thumbnail=300 -frames:v 1 -y #{vp.path}")
-    raise "ffmpeg failed: #{ffmpeg_out}" if !status.success?
-    Rails.logger.debug(ffmpeg_out)
+    output = shell!("ffmpeg -i #{file.path.shellescape} -vf thumbnail=300 -frames:v 1 -y #{vp.path.shellescape}")
+    Rails.logger.debug(output)
 
     MediaFile.open(vp)
   end
+
+  # Get file metadata using ffprobe.
+  # @see https://ffmpeg.org/ffprobe.html
+  # @see https://gist.github.com/nrk/2286511
+  # @return [Hash] a hash of the file's metadata
+  def metadata
+    output = shell!("ffprobe -v quiet -print_format json -show_format -show_streams #{file.path.shellescape}")
+    json = JSON.parse(output)
+    json.with_indifferent_access
+  end
+
+  def width
+    video_channels.first[:width]
+  end
+
+  def height
+    video_channels.first[:height]
+  end
+
+  def duration
+    metadata.dig(:format, :duration).to_f
+  end
+
+  def video_channels
+    metadata[:streams].select { |stream| stream[:codec_type] == "video" }
+  end
+
+  def audio_channels
+    metadata[:streams].select { |stream| stream[:codec_type] == "audio" }
+  end
+
+  def has_audio?
+    audio_channels.present?
+  end
+
+  def shell!(command)
+    program = command.shellsplit.first
+    output, status = Open3.capture2e(command)
+    raise Error, "#{program} failed: #{output}" if !status.success?
+    output
+  end
+
+  memoize :metadata
 end

app/logical/media_file/video.rb

@@ -3,14 +3,12 @@
 #
 # @see https://github.com/streamio/streamio-ffmpeg
 class MediaFile::Video < MediaFile
+  delegate :duration, :has_audio?, to: :video
+
   def dimensions
     [video.width, video.height]
   end
 
-  def duration
-    video.duration
-  end
-
   def preview(max_width, max_height)
     preview_frame.preview(max_width, max_height)
   end
@@ -19,20 +17,14 @@ class MediaFile::Video < MediaFile
     preview_frame.crop(max_width, max_height)
   end
 
-  def has_audio?
-    video.audio_channels.present?
-  end
-
   private
 
   def video
-    raise NotImplementedError, "can't process videos: ffmpeg or mkvmerge not installed" unless self.class.videos_enabled?
-
-    FFMPEG::Movie.new(file.path)
+    FFmpeg.new(file)
   end
 
   def preview_frame
-    FFmpeg.new(file).smart_video_preview
+    video.smart_video_preview
   end
 
   memoize :video, :preview_frame, :dimensions, :duration, :has_audio?