Fix MP4 (H264 + AAC) video files being needlessly re-encoded (#13239)

app/models/media_attachment.rb

@@ -77,6 +77,22 @@ class MediaAttachment < ApplicationRecord
     },
   }.freeze
 
+  VIDEO_PASSTHROUGH_OPTIONS = {
+    video_codec_whitelist: ['h264'],
+    audio_codec_whitelist: ['aac', nil],
+    options: {
+      format: 'mp4',
+      convert_options: {
+        output: {
+          'loglevel' => 'fatal',
+          'map_metadata' => '-1',
+          'c:v' => 'copy',
+          'c:a' => 'copy',
+        },
+      },
+    },
+  }.freeze
+
   VIDEO_STYLES = {
     small: {
       convert_options: {
@@ -91,7 +107,7 @@ class MediaAttachment < ApplicationRecord
       blurhash: BLURHASH_OPTIONS,
     },
 
-    original: VIDEO_FORMAT,
+    original: VIDEO_FORMAT.merge(passthrough_options: VIDEO_PASSTHROUGH_OPTIONS),
   }.freeze
 
   AUDIO_STYLES = {

lib/paperclip/video_transcoder.rb

@@ -5,12 +5,20 @@ module Paperclip
   # to check when uploaded videos are actually gifv's
   class VideoTranscoder < Paperclip::Processor
     def make
-      meta = ::Av.cli.identify(@file.path)
+      movie = FFMPEG::Movie.new(@file.path)
+      actual_options = options
+      passthrough_options = actual_options[:passthrough_options]
+      actual_options = passthrough_options[:options] if passthrough?(movie, passthrough_options)
 
-      attachment.instance.type = MediaAttachment.types[:gifv] unless meta[:audio_encode]
-      options[:format] = File.extname(attachment.instance.file_file_name)[1..-1] if options[:keep_same_format]
+      attachment.instance.type = MediaAttachment.types[:gifv] unless movie.audio_codec
 
-      Paperclip::Transcoder.make(file, options, attachment)
+      Paperclip::Transcoder.make(file, actual_options, attachment)
+    end
+
+    private
+
+    def passthrough?(movie, options)
+      options && options[:video_codec_whitelist].include?(movie.video_codec) && options[:audio_codec_whitelist].include?(movie.audio_codec)
     end
   end
 end