media assets: save more metadata for videos.

Include the following metadata tags for videos:

* FFmpeg:MajorBrand (e.g. mp42)
* FFmpeg:PixFmt (e.g. yuv420p. Indicates bit depth and color subsampling mode)
* FFmpeg:FrameCount (e.g. total number of frames in the video)
* FFmpeg:VideoCodec (e.g. h264)
* FFmpeg:VideoProfile (e.g. Main)
* FFmpeg:AudioCodec (e.g. AAC)
* FFmpeg:AudioProfile (e.g. LC)
* FFmpeg:AudioLayout (e.g. stereo)
* FFmpeg:AudioBitRate (e.g. 128kb/s)

app/logical/ffmpeg.rb

@@ -83,6 +83,10 @@ class FFmpeg
     frame_count / duration
   end
 
+  def major_brand
+    metadata.dig(:format, :tags, :major_brand)
+  end
+
   def pix_fmt
     video_stream[:pix_fmt]
   end
@@ -99,6 +103,14 @@ class FFmpeg
     metadata[:streams].to_a.select { |stream| stream[:codec_type] == "video" }
   end
 
+  def audio_codec
+    audio_stream[:codec_name]
+  end
+
+  def audio_stream
+    audio_streams.first || {}
+  end
+
   def audio_streams
     metadata[:streams].to_a.select { |stream| stream[:codec_type] == "audio" }
   end

app/logical/media_file/video.rb

@@ -5,7 +5,7 @@
 #
 # @see https://github.com/streamio/streamio-ffmpeg
 class MediaFile::Video < MediaFile
-  delegate :duration, :frame_count, :frame_rate, :has_audio?, :is_corrupt?, :pix_fmt, :video_codec, :video_stream, :video_streams, :audio_streams, :error, to: :video
+  delegate :duration, :frame_count, :frame_rate, :has_audio?, :is_corrupt?, :major_brand, :pix_fmt, :video_codec, :video_stream, :video_streams, :audio_codec, :audio_stream, :audio_streams, :error, to: :video
 
   def dimensions
     [video.width, video.height]
@@ -16,7 +16,18 @@ class MediaFile::Video < MediaFile
   end
 
   def metadata
-    super.merge({ "FFmpeg:Error" => error }.compact_blank)
+    super.merge({
+      "FFmpeg:Error" => error,
+      "FFmpeg:MajorBrand" => major_brand,
+      "FFmpeg:PixFmt" => pix_fmt,
+      "FFmpeg:FrameCount" => frame_count,
+      "FFmpeg:VideoCodec" => video_codec,
+      "FFmpeg:VideoProfile" => video_stream[:profile],
+      "FFmpeg:AudioCodec" => audio_codec,
+      "FFmpeg:AudioProfile" => audio_stream[:profile],
+      "FFmpeg:AudioLayout" => audio_stream[:channel_layout],
+      "FFmpeg:AudioBitRate" => audio_stream[:bit_rate],
+    }.compact_blank)
   end
 
   def is_supported?