diff --git a/lib/decode/file b/lib/decode/file
index aa3ce75..2666e11 100644
--- a/lib/decode/file
+++ b/lib/decode/file
@@ -1,12 +1,34 @@
 #!/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.
+
+# soxtaskid persists across destinations so encode tasks share a single sox task
 declare soxtaskid
 decodeFile() {
+	# copy destinations bypass decoding entirely
 	if [[ ${destinationformat["$destination"]} == copy ]]
 	then
 		copied=1
 	else
+		# Dispatch to the appropriate decoder based on the source
+		# MIME type.
+		# sox_needed is set when normalization, resampling, or channel
+		# up/downmixing is required. Used to determine whether to
+		# insert an intermediate sox processing task.
 		case "$mimetype" in
 			'video/'*)
+				# Extract audio if ffmpeg is available
 				(( disablevideo )) && continue
 				extractAudio
 				if (( ${destinationnormalize["$destination"]}))\
@@ -22,6 +44,8 @@ decodeFile() {
 				fi
 			;;
 			'audio/mpeg')
+				# Copy MP3 as-is if format and quality match
+				# otherwise decode with sox
 				if [[ ${destinationformat[$destination]} = mp3 ]] \
 				&& checkCopy
 				then
@@ -30,7 +54,9 @@ decodeFile() {
 					decodeSox
 				fi
 			;;
-			'application/ogg opus')
+			'application/ogg opus'|'audio/ogg opus')
+				# Copy Opus as-is if format and quality match
+				# otherwise decode with opusdec
 				if [[ ${destinationformat[$destination]} = opus ]] \
 				&& checkCopy
 				then
@@ -51,28 +77,9 @@ decodeFile() {
 					fi
 				fi
 			;;
-			'audio/ogg opus')
-				if [[ ${destinationformat[$destination]} = opus ]] \
-				&& checkCopy
-				then
-					copied=1
-				else
-					(( disableopusdec )) && continue
-					decodeOpusdec
-					if (( ${destinationnormalize["$destination"]}))\
-					|| (
-					[ -n "${destinationfrequency["$destination"]}" ]\
-					&& (( ${rate:-0} != ${destinationfrequency["$destination"]}))\
-					) || (
-					[ -n "${destinationchannels["$destination"]}" ]\
-					&& (( ${channels:-0} != ${destinationchannels["$destination"]} ))
-					)
-					then
-						sox_needed=1
-					fi
-				fi
-			;;
-			'application/ogg'*)
+			'application/ogg'*|'audio/ogg'*)
+				# Ogg Vorbis: copy if format/quality match
+				# otherwise decode with sox
 				if [[ ${destinationformat[$destination]} = vorbis ]] \
 				&& checkCopy
 				then
@@ -81,22 +88,14 @@ decodeFile() {
 					decodeSox
 				fi
 			;;
-			'audio/ogg'*)
-				if [[ ${destinationformat[$destination]} = vorbis ]] \
-				&& checkCopy
-				then
-					copied=1
-				else
-					decodeSox
-				fi
-			;;
-			'audio/x-flac')
-				decodeSox
-			;;
-			'audio/flac')
+			'audio/x-flac'|'audio/flac')
+				# FLAC: always decode via sox
+				# copy for FLAC makes little sense
 				decodeSox
 			;;
 			*)
+				# Unknown MIME type: probe with file to detect
+				# Musepack
 				extendedtype=$(file -b "$sourcepath/$filename")
 				case "$extendedtype" in
 					*'Musepack '*)
@@ -115,6 +114,9 @@ decodeFile() {
 						fi
 					;;
 					*)
+						# Truly unknown format: try
+						# ffmpeg if available,
+						# otherwise fall back to sox
 						if (( disablevideo ))
 						then
 							decodeSox
@@ -138,6 +140,10 @@ decodeFile() {
 		esac
 		if ! (( copied ))
 		then
+			# Insert a decode task if one doesn't already exist for
+			# this source file
+			# keyed by $tmpfile so multiple destinations share a
+			# single decode task
 			if ! decodetaskid=$(
 				Select tasks id <<<"key = $tmpfile"
 			)
@@ -160,11 +166,18 @@ decodeFile() {
 			fi
 			if (( sox_needed ))
 			then
+				# Insert a sox post-processing task chained
+				# after the decode task
 				decodeSox "$tempdir/$tmpfile.wav"
 				if ! soxtaskid=$(
 					Select tasks id <<<"key = $tmpfile"
 				)
 				then
+					# Increment the decode task's
+					# required_by counter so cleaner()
+					# waits for all dependent tasks to
+					# finish before cleaning up the
+					# intermediate file
 					parent_required=$(
 						Select tasks required_by			\
 							<<<"id = $decodetaskid"
diff --git a/lib/decode/mpcdec b/lib/decode/mpcdec
index c0621ff..fe9edaf 100644
--- a/lib/decode/mpcdec
+++ b/lib/decode/mpcdec
@@ -1,6 +1,26 @@
 #!/bin/bash
+
+# Copyright © 2012-2026 ScriptFanix
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# A copy of the GNU General Public License v3 is includded in the LICENSE file
+# at the root of the project.
+
 decodeMpcdec() {
+	# Set the tmpfile base name for this specific decode task
+	# source file id + decoder name
 	tmpfile="${fileid}mpcdec"
+	# Build mpcdec command: decode Musepack to WAV in tempdir
+	# ${ionice} prepends the ionice invocation string if configured
 	commandline=(${ionice}mpcdec)
+	# Encode any literal newlines in the filename as the SQL-safe inline
+	# marker
 	commandline+=("$sourcepath/${filename//$'\n'/::AtOM:NewLine:SQL:Inline::}" "$tempdir/$tmpfile.wav")
 }
diff --git a/lib/decode/opusdec b/lib/decode/opusdec
index b2cac97..39d4c67 100644
--- a/lib/decode/opusdec
+++ b/lib/decode/opusdec
@@ -1,6 +1,26 @@
 #!/bin/bash
+
+# Copyright © 2012-2026 ScriptFanix
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# A copy of the GNU General Public License v3 is includded in the LICENSE file
+# at the root of the project.
+
 decodeOpusdec() {
+	# Set the tmpfile base name for this specific decode task
+	# source file id + decoder name
 	tmpfile="${fileid}opusdec"
+	# Build opusdec command: decode Opus to WAV in tempdir
+	# ${ionice} prepends the ionice invocation string if configured
 	commandline=(${ionice}opusdec)
+	# Encode any literal newlines in the filename as the SQL-safe inline
+	# marker
 	commandline+=("$sourcepath/${filename//$'\n'/::AtOM:NewLine:SQL:Inline::}" "$tempdir/$tmpfile.wav")
 }
diff --git a/lib/decode/sox b/lib/decode/sox
index e12bf4c..1bbfbe4 100644
--- a/lib/decode/sox
+++ b/lib/decode/sox
@@ -1,36 +1,67 @@
 #!/bin/bash
+
+# Copyright © 2012-2026 ScriptFanix
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# A copy of the GNU General Public License v3 is includded in the LICENSE file
+# at the root of the project.
+
 decodeSox() {
+	# Build a SoX decode command with optional processing (normalize,
+	# resample, up/downmix)
 	commandline=(${ionice}sox --single-threaded --temp "$tempdir")
 	soxoptions_in=''
 	soxoptions_out=''
+
+	# Add --norm if output normalization is requested
 	if (( ${destinationnormalize["$destination"]} ))
 	then
 		commandline+=(--norm)
 		soxoptions_in+=' --norm'
 	fi
+
+	# $1 can be set to pass an already decoded file.
+	# Use the the original file when unset
 	if [ -n "$1" ]
 	then
 		commandline+=("$1")
 	else
 		commandline+=("$sourcepath/${filename//$'\n'/::AtOM:NewLine:SQL:Inline::}")
 	fi
+
+	# Add resampling if requested
 	if [ -n "${destinationfrequency["$destination"]}" ]	\
 	&& (( ${rate:-0} != ${destinationfrequency["$destination"]} ))
 	then
 		commandline+=(-r ${destinationfrequency["$destination"]})
 		soxoptions_out+=" -r ${destinationfrequency["$destination"]}"
 	fi
+
+	# Add channel up/downmixing if requested
 	if [ -n "${destinationchannels["$destination"]}" ]	\
 	&& (( ${channels:-0} != ${destinationchannels["$destination"]} ))
 	then
 		commandline+=(-c ${destinationchannels["$destination"]})
 		soxoptions_out+=" -c ${destinationchannels["$destination"]}"
 	fi
+
+	# Downsample to 16-bit if source resolution exceeds 16 bits
 	if (( ${depth:-0} > 16 ))
 	then
 		commandline+=(-b 16)
 		soxoptions_out+=" -b 16"
 	fi
+
+	# Encode all sox options into the tmpfile name so different processing
+	# chains get unique WAV files
+	# Avoids conflicts with different samplerate/norm/channel counts
 	tmpfile="$fileid${soxoptions_in// /}${soxoptions_out// /}"
 	commandline+=("$tempdir/$tmpfile.wav")
 }