perform loudness normalization

Author: vchuravy

processing.jl

@@ -5,6 +5,39 @@ using JSON
 const preroll = ARGS[1]
 const file = ARGS[2]
 
+const target_il =  -24.0
+const target_lra = +11.0
+const target_tp = -2.0
+
+const loudnorm_query = "loudnorm=dual_mono=true:I=$(target_il):LRA=$(target_lra):tp=$(target_tp)"
+
+function query_loudness(file)
+  output_lines = FFMPEG.exe(`-i $file -filter:a $(loudnorm_query*":print_format=json") -vn -sn -f null NULL`, collect=true)
+
+  loudnorm_start = nothing
+  loudnorm_end = nothing
+  for (i,line) in enumerate(output_lines)
+    if startswith(line, "[Parsed_loudnorm")
+      loudnorm_start = i + 1
+      continue
+    end 
+
+    if loudnorm_start !== nothing && startswith(line, "}")
+      loudnorm_end = i
+      continue
+    end
+  end
+
+  if loudnorm_end === nothing || loudnorm_start === nothing
+    error("Failed to parse ffmpeg output")
+  end
+
+  json = join(output_lines[loudnorm_start:loudnorm_end], "\n")
+  properties = JSON.Parser.parse(json)
+end
+
+format_loudnorm(p) = loudnorm_query * ":linear=true:measured_I=$(p["input_i"]):measured_LRA=$(p["input_lra"]):measured_tp=$(p["input_tp"]):measured_thresh=$(p["input_thresh"]):offset=$(p["target_offset"])"
+
 # 1. Query properties of file
 
 json = join(FFMPEG.exe(`-v error -show_entries stream=width,height -of json $(file)`, command=FFMPEG.ffprobe, collect=true), "\n")
@@ -17,13 +50,22 @@ sizes = map(stream -> (stream["width"], stream["height"]), streams)
 unique!(sizes)
 width, height = only(sizes)
 
+@sync begin
+  global query0 = @async query_loudness(preroll)
+  global query1 = @async query_loudness(file)
+end
+audio0_properties = fetch(query0)
+audio1_properties = fetch(query1)
+
 args = ```
 -i $(preroll)
 -i $(file)
 -filter_complex 
 "[0:v]scale=$(width):$(height):force_original_aspect_ratio=decrease,pad=$(width):$(height):-1:-1,setsar=1,fps=30,format=yuv420p[v0]; \
  [1:v]setsar=1,fps=30,format=yuv420p[v1];
-  [v0][0:a][v1][1:a]concat=n=2:v=1:a=1[v][a]"
+ [0:a]$(format_loudnorm(audio0_properties))[a0];
+ [1:a]$(format_loudnorm(audio1_properties))[a1];
+  [v0][a0][v1][a1]concat=n=2:v=1:a=1[v][a]"
 -map "[v]"
 -map "[a]"
 -c:v libx264
@@ -35,6 +77,4 @@ args = ```
 out/$(file)
 ```
 
-@show args
 FFMPEG.exe(args)
-