1 files changed, 118 insertions, 0 deletions
diff --git a/activestorage/lib/active_storage/analyzer/video_analyzer.rb b/activestorage/lib/active_storage/analyzer/video_analyzer.rb
new file mode 100644
index 0000000000..18d8ff8237
--- /dev/null
+++ b/activestorage/lib/active_storage/analyzer/video_analyzer.rb
@@ -0,0 +1,118 @@
+# frozen_string_literal: true
+
+module ActiveStorage
+  # Extracts the following from a video blob:
+  #
+  # * Width (pixels)
+  # * Height (pixels)
+  # * Duration (seconds)
+  # * Angle (degrees)
+  # * Display aspect ratio
+  #
+  # Example:
+  #
+  #   ActiveStorage::VideoAnalyzer.new(blob).metadata
+  #   # => { width: 640.0, height: 480.0, duration: 5.0, angle: 0, display_aspect_ratio: [4, 3] }
+  #
+  # When a video's angle is 90 or 270 degrees, its width and height are automatically swapped for convenience.
+  #
+  # This analyzer requires the {FFmpeg}[https://www.ffmpeg.org] system library, which is not provided by Rails.
+  class Analyzer::VideoAnalyzer < Analyzer
+    def self.accept?(blob)
+      blob.video?
+    end
+
+    def metadata
+      { width: width, height: height, duration: duration, angle: angle, display_aspect_ratio: display_aspect_ratio }.compact
+    end
+
+    private
+      def width
+        if rotated?
+          computed_height || encoded_height
+        else
+          encoded_width
+        end
+      end
+
+      def height
+        if rotated?
+          encoded_width
+        else
+          computed_height || encoded_height
+        end
+      end
+
+      def duration
+        Float(video_stream["duration"]) if video_stream["duration"]
+      end
+
+      def angle
+        Integer(tags["rotate"]) if tags["rotate"]
+      end
+
+      def display_aspect_ratio
+        if descriptor = video_stream["display_aspect_ratio"]
+          if terms = descriptor.split(":", 2)
+            numerator   = Integer(terms[0])
+            denominator = Integer(terms[1])
+
+            [numerator, denominator] unless numerator == 0
+          end
+        end
+      end
+
+
+      def rotated?
+        angle == 90 || angle == 270
+      end
+
+      def computed_height
+        if encoded_width && display_height_scale
+          encoded_width * display_height_scale
+        end
+      end
+
+      def encoded_width
+        @encoded_width ||= Float(video_stream["width"]) if video_stream["width"]
+      end
+
+      def encoded_height
+        @encoded_height ||= Float(video_stream["height"]) if video_stream["height"]
+      end
+
+      def display_height_scale
+        @display_height_scale ||= Float(display_aspect_ratio.last) / display_aspect_ratio.first if display_aspect_ratio
+      end
+
+
+      def tags
+        @tags ||= video_stream["tags"] || {}
+      end
+
+      def video_stream
+        @video_stream ||= streams.detect { |stream| stream["codec_type"] == "video" } || {}
+      end
+
+      def streams
+        probe["streams"] || []
+      end
+
+      def probe
+        download_blob_to_tempfile { |file| probe_from(file) }
+      end
+
+      def probe_from(file)
+        IO.popen([ ffprobe_path, "-print_format", "json", "-show_streams", "-v", "error", file.path ]) do |output|
+          JSON.parse(output.read)
+        end
+      rescue Errno::ENOENT
+        logger.info "Skipping video analysis because FFmpeg isn't installed"
+        {}
+      end
+
+      def ffprobe_path
+        ActiveStorage.paths[:ffprobe] || "ffprobe"
+      end
+  end
+end