diff --git a/lib/copy/action b/lib/copy/action
index b49aea7..c0a90ba 100644
--- a/lib/copy/action
+++ b/lib/copy/action
@@ -1,6 +1,25 @@
 #!/bin/bash
+
+# Copyright © 2012-2026 ScriptFanix
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# A copy of the GNU General Public License v3 is includded in the LICENSE file
+# at the root of the project.
+
 copyFiles_action() {
 	(( cron )) || echo -n $'Copying files...\033[K'
+	# Query all destination_files whose last_change doesn't match the
+	# source, restricted to mime_type_actions with action=2 (direct copy,
+	# not transcode).
+	# The join on mime_type_actions ensures we only copy files destined for
+	# a destination that has explicitly mapped this MIME type to action=2.
 	echo '
 		SELECT
 			source_files.filename,
@@ -22,6 +41,8 @@ copyFiles_action() {
 		AND	mime_type_actions.action = 2;
 
 		SELECT "AtOM:NoMoreFiles";' >&3
+	# Results are NUL-delimited rows; sentinel value signals end of result
+	# set.
 	read -u4 -r -d $'\0' line
 	while ! [[ $line = AtOM:NoMoreFiles ]]
 	do
@@ -29,9 +50,14 @@ copyFiles_action() {
 		read -u4 -r -d $'\0' line
 	done
 
+	# Wrap all DB updates in a single transaction for performance.
 	echo 'BEGIN TRANSACTION;' >&3
 	for copyfile in "${copyfiles[@]}"
 	do
+		# Each row is a single string with columns joined by
+		# ::AtOM:SQL:Sep::.
+		# Strip prefix to extract each field in order, advancing $rest
+		# each time.
 		sourcefilename=${copyfile%%::AtOM:SQL:Sep::*}
 		sourcedir=${sourcefilename%/*}
 		rest="${copyfile#*::AtOM:SQL:Sep::}::AtOM:SQL:Sep::"
@@ -45,20 +71,33 @@ copyFiles_action() {
 		rest=${rest#*::AtOM:SQL:Sep::}
 		(( count++ ))
 		(( cron )) || printf '\b\b\b\b%3i%%' $(( (count * 100) / ${#copyfiles[@]} ))
+		# If this destination uses a rename/path pattern, delegate path
+		# resolution to guessPath(), which looks up the
+		# already-transcoded sibling to find the correct output
+		# directory.
 		if [ -n "${destinationrenamepath["$destination"]}" ]
 		then
 			destdir="$(guessPath)"
 			guessstatus=$?
 			case $guessstatus in
 				1)
+					# guessPath found no transcoded
+					# sibling; skip this file entirely.
 					continue
 				;;
 				2)
+					# Transcoded siblings exist but are not
+					# yet up to date; defer this copy until
+					# the next run so the directory is
+					# stable.
 					(( postponed++ ))
 					continue
 				;;
 			esac
 		else
+			# No rename pattern: mirror the source directory
+			# structure under the destination root, sanitizing each
+			# path component for the target FS.
 			destdir="${destinationpath["$destination"]}/"
 			if [[ $sourcefilename =~ / ]]
 			then
@@ -79,6 +118,9 @@ copyFiles_action() {
 				fi
 			fi
 		fi
+		# Try the cheapest copy methods first: reflink (CoW, same
+		# filesystem), then hardlink (csame filesystem), falling back
+		# to a full data copy.
 		if cp -a --reflink=always		\
 			"$sourcepath/$sourcefilename"	\
 			"$destdir"			\
@@ -91,6 +133,9 @@ copyFiles_action() {
 			"$sourcepath/$sourcefilename"	\
 			"$destdir"
 		then
+			# Newlines in filenames are stored as a safe inline
+			# placeholder so the value can be embedded in SQL
+			# without breaking row parsing.
 			destfilename=${sourcefilename//$'\n'/::AtOM:NewLine:SQL:Inline::}
 			Update destination_files			\
 				filename				\
diff --git a/lib/copy/check b/lib/copy/check
index 44738dd..c6a37ad 100644
--- a/lib/copy/check
+++ b/lib/copy/check
@@ -1,12 +1,39 @@
 #!/bin/bash
+
+# Copyright © 2012-2026 ScriptFanix
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# A copy of the GNU General Public License v3 is includded in the LICENSE file
+# at the root of the project.
+
 checkCopy() {
+	# Returns true only when the source file is compatible enough with the
+	# destination profile that it can be copied instead of re-encoded.
+	# All three conditions must hold simultaneously.
 	(
+		# If the destination doesn't restrict sample rate, any rate is
+		# acceptable. Otherwise the source rate must match exactly.
 		[ -z "${destinationfrequency[$destination]}" ]		\
 		|| (( ${rate:-0} == ${destinationfrequency[$destination]} ))
 	) && (
+		# If the destination doesn't restrict channel count, any number
+		# is acceptable. Otherwise the source channel count must match
+		# exactly.
 		[ -z "${destinationchannels[$destination]}" ]		\
 		|| (( ${channels:-0} == ${destinationchannels[$destination]} ))
 	) && (
+		# Bitrate check: accept if source exactly matches the target
+		# quality setting, OR if a maximum bps ceiling is configured
+		# and the source bitrate is at or below it.
+		# Default of 1000 kbps when bitrate is unknown forces a
+		# re-encode
 		(( ${bitrate:-1000} == ${destinationquality[$destination]} ))	\
 		|| (
 			[ -n "${destinationmaxbps[$destination]}" ]	\
diff --git a/lib/copy/guessPath b/lib/copy/guessPath
index f7f0926..b60b7c7 100644
--- a/lib/copy/guessPath
+++ b/lib/copy/guessPath
@@ -1,6 +1,29 @@
 #!/bin/bash
 
+# Copyright © 2012-2026 ScriptFanix
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# A copy of the GNU General Public License v3 is includded in the LICENSE file
+# at the root of the project.
+
 guessPath() {
+	# For copy files (action=2) with a rename pattern, we don't know the
+	# output directory ourselves: it was determined when the audio siblings
+	# were transcoded (action=1). We infer it by finding a transcoded
+	# sibling in the same source directory and reading back its destination
+	# path.
+	#
+	# First query: check whether any transcoded sibling is up to date.
+	# The LIKE pattern matches files directly inside $sourcedir only
+	# the NOT LIKE excludes deeper subdirectorie to avoid crossing
+	# boundaries.
 	echo 'SELECT IFNULL( (
 		SELECT	destination_files.last_change
 		FROM		destination_files
@@ -22,10 +45,17 @@ guessPath() {
 	),"0.0");
 	'>&3
 	read -u4 -r -d $'\0' timestamp
+	# IFNULL returns "0.0" when no transcoded sibling exists yet; strip the
+	# decimal and treat as zero to detect the no-sibling case.
 	if (( ${timestamp/./} == 0 ))
 	then
+		# No transcoded sibling found at all
+		# caller should postpone this copy.
 		return 2
 	fi
+	# Second query: retrieve the actual destination filename of the most
+	# recently updated transcoded sibling so we can derive its parent
+	# directory.
 	echo 'SELECT IFNULL( (
 		SELECT	destination_files.filename
 		FROM		destination_files
@@ -49,8 +79,12 @@ guessPath() {
 	read -u4 -r -d $'\0' filename
 	if [[ $filename != AtOM:NotFound ]]
 	then
+		# Strip the filename component to return only the directory
+		# portion.
 		echo "${filename%/*}"
 	else
+		# Sibling record exists but has no usable filename — skip this
+		# file.
 		return 1
 	fi
 }
diff --git a/lib/copy/matching b/lib/copy/matching
index 73087a0..5240a0b 100644
--- a/lib/copy/matching
+++ b/lib/copy/matching
@@ -1,6 +1,25 @@
 #!/bin/bash
+
+# Copyright © 2012-2026 ScriptFanix
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# A copy of the GNU General Public License v3 is includded in the LICENSE file
+# at the root of the project.
+
 copyFiles_matching() {
+	# Preserve the original file extension so the copy keeps its type
+	# (e.g. .jpg, .png, .cue) regardless of any rename pattern applied to
+	# the base name.
 	local extension="${filename##*.}"
+	# Try hardlink first (no extra disk space); fall back to a full data
+	# copy if the source and destination are on different filesystems.
 	if					\
 	cp -al					\
 		"$sourcepath/$filename"		\
@@ -10,6 +29,11 @@ copyFiles_matching() {
 		"$sourcepath/$filename"		\
 		"${destinationpath[$destination]}/$destdir/$destfile.$extension"
 	then
+		# Record the new destination path and copy the source
+		# last_change timestamp via a subquery so the DB reflects when
+		# the source was last modified.
+		# old_filename captures the previous path so stale files can be
+		# cleaned up later.
 		echo							\
 			"UPDATE	destination_files"			\
 			"SET filename="					\