Change video compression parameters (#26631)

app/models/media_attachment.rb

@@ -44,6 +44,7 @@ class MediaAttachment < ApplicationRecord
 
   MAX_VIDEO_MATRIX_LIMIT = 8_294_400 # 3840x2160px
   MAX_VIDEO_FRAME_RATE   = 120
+  MAX_VIDEO_FRAMES       = 36_000 # Approx. 5 minutes at 120 fps
 
   IMAGE_FILE_EXTENSIONS = %w(.jpg .jpeg .png .gif .webp .heic .heif .avif).freeze
   VIDEO_FILE_EXTENSIONS = %w(.webm .mp4 .m4v .mov).freeze
@@ -98,17 +99,12 @@ class MediaAttachment < ApplicationRecord
     convert_options: {
       output: {
         'loglevel' => 'fatal',
-        'movflags' => 'faststart',
-        'pix_fmt' => 'yuv420p',
-        'vf' => 'scale=\'trunc(iw/2)*2:trunc(ih/2)*2\'',
-        'vsync' => 'cfr',
+        'preset' => 'veryfast',
         'c:v' => 'h264',
-        'maxrate' => '1300K',
-        'bufsize' => '1300K',
-        'b:v' => '1300K',
-        'frames:v' => 60 * 60 * 3,
-        'crf' => 18,
+        'c:a' => 'aac',
+        'b:a' => '192k',
         'map_metadata' => '-1',
+        'frames:v' => MAX_VIDEO_FRAMES,
       }.freeze,
     }.freeze,
   }.freeze
@@ -135,7 +131,7 @@ class MediaAttachment < ApplicationRecord
       convert_options: {
         output: {
           'loglevel' => 'fatal',
-          :vf => 'scale=\'min(400\, iw):min(400\, ih)\':force_original_aspect_ratio=decrease',
+          :vf => 'scale=\'min(640\, iw):min(640\, ih)\':force_original_aspect_ratio=decrease',
         }.freeze,
       }.freeze,
       format: 'png',

lib/paperclip/transcoder.rb

@@ -4,6 +4,9 @@ module Paperclip
   # This transcoder is only to be used for the MediaAttachment model
   # to check when uploaded videos are actually gifv's
   class Transcoder < Paperclip::Processor
+    # This is the H.264 "High" value taken from https://www.dr-lex.be/info-stuff/videocalc.html
+    BITS_PER_PIXEL = 0.11
+
     def initialize(file, options = {}, attachment = nil)
       super
 
@@ -38,8 +41,11 @@ module Paperclip
         @output_options['vframes'] = 1
       when 'mp4'
         unless eligible_to_passthrough?(metadata)
-          @output_options['acodec'] = 'aac'
-          @output_options['strict'] = 'experimental'
+          bitrate = (metadata.width * metadata.height * 30 * BITS_PER_PIXEL) / 1_000
+
+          @output_options['b:v']     = "#{bitrate}k"
+          @output_options['maxrate'] = "#{bitrate + 192}k"
+          @output_options['bufsize'] = "#{bitrate * 5}k"
 
           if high_vfr?(metadata)
             @output_options['vsync'] = 'vfr'