From 76f6c862913ffd0ecf28d7bd5531ab5879b99920 Mon Sep 17 00:00:00 2001
From: wisp3rwind <17089248+wisp3rwind@users.noreply.github.com>
Date: Tue, 15 Mar 2022 23:12:45 +0100
Subject: [PATCH] replaygain: in ffmpeg backend, analyse items upfront, then
 summarize...

...album gains. This is in preparation for parallelizing the track
analysis, and computing the album values in the plugin's "main thread"
once all items are done.
---
 beetsplug/replaygain.py | 42 +++++++++++++++++++++++------------------
 1 file changed, 24 insertions(+), 18 deletions(-)

diff --git a/beetsplug/replaygain.py b/beetsplug/replaygain.py
index e26273cc3..45ff71ef1 100644
--- a/beetsplug/replaygain.py
+++ b/beetsplug/replaygain.py
@@ -288,17 +288,16 @@ class FfmpegBackend(Backend):
         """Computes the track gain for the tracks belonging to `task`, and sets
         the `track_gains` attribute on the task. Returns `task`.
         """
-        gains = []
-        for item in task.items:
-            gains.append(
-                self._analyse_item(
-                    item,
-                    task.target_level,
-                    task.peak_method,
-                    count_blocks=False,
-                )[0]  # take only the gain, discarding number of gating blocks
-            )
-        task.track_gains = gains
+        task.track_gains = [
+            self._analyse_item(
+                item,
+                task.target_level,
+                task.peak_method,
+                count_blocks=False,
+            )[0]  # take only the gain, discarding number of gating blocks
+            for item in task.items
+        ]
+
         return task
 
     def compute_album_gain(self, task):
@@ -308,8 +307,20 @@ class FfmpegBackend(Backend):
         target_level_lufs = db_to_lufs(task.target_level)
 
         # analyse tracks
+        # Gives a list of tuples (track_gain, track_n_blocks)
+        track_results = [
+            self._analyse_item(
+                item,
+                task.target_level,
+                task.peak_method,
+                count_blocks=True,
+            )
+            for item in task.items
+        ]
+
         # list of track Gain objects
-        track_gains = []
+        track_gains = [tg for tg, _nb in track_results]
+
         # maximum peak
         album_peak = 0
         # sum of BS.1770 gating block powers
@@ -317,12 +328,7 @@ class FfmpegBackend(Backend):
         # total number of BS.1770 gating blocks
         n_blocks = 0
 
-        for item in task.items:
-            track_gain, track_n_blocks = self._analyse_item(
-                item, task.target_level, task.peak_method
-            )
-            track_gains.append(track_gain)
-
+        for (track_gain, track_n_blocks) in track_results:
             # album peak is maximum track peak
             album_peak = max(album_peak, track_gain.peak)