FFOPTS and default behavior doesn't re-encode.

README.md

@@ -1,41 +1,89 @@
+# Get Tracks
+
+`get-tracks.sh` allows you to easily extract music tracks from a file with multiple songs, like a CD-in-a-file.
+
 # Required applications
 
-* ffmpeg
-* xxd (with '-r' and '-p' options)
-* awk
+`get-tracks.sh` is a simple shell script based around `ffmpeg`, using only POSIX tools.
+
+It was tested on both OpenBSD and Linux (Ubuntu, Alpine).
 
 # Usage
 
+Download a CD and the starting time of each track in a file, and you're good to go.
+
 ```Bash
-get-tracks.sh rip <audio-file> <time-file>
+get-tracks.sh <audio-file> <time-file>
 
 # Example
-get-track.sh rip doom-eternal.opus doom-eternal.txt
+get-track.sh doom-eternal.opus doom-eternal.txt
 ```
 
 
-`audio-file` can be in any format understood by `ffmpeg`.
+*audio-file* can be in any format understood by `ffmpeg`.
 
-The `time-file` must have this format:
+The *time-file* must have this format:
 
 ```
-0:00 First song
-2:20 Second song
+0:00 intro
+2:20 First song
 3:18 Awesome song
 ```
 
 # Environment variables
 
-* **SIMULATION**: if non empty do not invoke ffmpeg
-* **FORMAT** [mp3,ogg,opus,…]: for the song file format
-* **NONUMBER**: if equals to 1, do not write song number
-* **SEPARATOR**: (default: ' - '), write song number, with this separator
-  example with SEPARATOR='_': song names will be 01_song.opus 02_song.opus…
-* **VERBOSITY** [0-3] (default: 1)\
-  verbosity 0: no output except errors from ffmpeg\
-  verbosity 1: simple indications on the current track being extracted\
-  verbosity 2: print actual ffmpeg commands the script currently runs
+The behavior of the script can be changed by several environment variables.
+
+* **SIMULATION** [empty or not]\
+    do not invoke ffmpeg
+
+* **FORMAT** [mp3,ogg,opus,…]\
+    see the ffmpeg documentation for the output formats available
+* **FFOPTS** [any ffmpeg options] *(default: '-c:a copy')*\
+    ffmpeg options, can be used to change audio quality\
+    can be **required** to change in case input and output file formats differ\
+    see the ffmpeg documentation for available parameters
+
+* **NONUMBER** [empty or 1]\
+    do not write song numbers
+* **SEPARATOR** [separator] *(default: ' - ')*\
+    separator between number and name\
+    example with SEPARATOR='_': 01_intro.opus 02_blah.opus…
+
+* **HEADERS** [empty or 1]\
+    print environment parameters (verbosity, simulation, etc.)
+* **VERBOSITY** [0-3] *(default: 1)*\
+    0: no output except errors from ffmpeg\
+    1: simple indications on the current track being extracted\
+    2: print actual ffmpeg commands the script currently runs
+
+# Different input and output file formats
+
+In case you want to change the file format, let's say from `flac` to `opus`, you need to override the default ffmpeg options provided by `get-tracks.sh`.
+This is done through the `FFOPTS` environment variable, **which needs to NOT be empty** in order to replace the default `get-tracks.sh` behavior (which is `-c:a copy`).
+By default, `ffmpeg` performs re-encoding by itself.
+
+```Bash
+FORMAT=opus FFOPTS=" " get-tracks.sh cd.flac cd.txt
+```
+
+### Warning: sometimes you don't even need to
+
+You may encounter files in some format like `webm` and you want to convert the output files in `opus`.
+But, inside the `webm` format, you **may** have `opus`-encoded audio.
+In these cases, no re-encoding is necessary, and you can do something like:
+
+```Bash
+FORMAT=opus get-tracks.sh cd.webm cd.txt
+```
+
+You'll have a warning mentionning FFOPTS (based on different formats).
+But the generated audio files won't have any quality loss.
+This happens sometimes with the `youtube-dl` utility.
+
+In case there are actual `ffmpeg` errors, and you don't have output audio files, then the contained audio hadn't the right format.
+You'll have to re-encode.
 
 # More
 
-Run `get-track.sh` without arguments.
+You can get some help by running `get-track.sh` without arguments.

get-tracks.sh

@@ -1,9 +1,9 @@
 #!/usr/bin/env sh
 
-# From a single byte in hexadecimal per line
-# to lines ending with 0a (hex for '\n').
-regroup_lines(){
-	awk '
+# From a single byte in hexadecimal per line to lines ending with 0a
+# (hex for '\n'). Ex: 61 62 63 0a
+# Required to easily match (and remove) multi-byte characters.
+regroup_lines() awk '
 	BEGIN {
 		line_start=1
 	}
@@ -26,45 +26,47 @@ regroup_lines(){
 			print line
 	}
 	'
-}
 
 # From ’ to '
-simple_quote(){
-	sed "s/e2 80 99/27/g"
-}
+simple_quote()                sed "s/e2 80 99/27/g"
 
-# From / to ' - '
-replace_slashes(){
-	sed "s/2f/20 2d 20/g"
-}
+# From / to '-'
+replace_slashes()             sed "s/2f/2d/g"
 
-remove_multibyte_characters(){
-	sed "s/e2 80 .. //g"
-}
+remove_backslashes()          sed "s/5c//g"
+
+remove_multibyte_characters() sed "s/e2 80 .. //g"
+
+uppercase()                   tr "[a-z]" "[A-Z]"
+
+# One column decimal to plain text.
+from_dec()                    awk '{ printf ("%c", $1 + 0) }'
+
+# Replace spaces by line returns, outputs a single column.
+spaces_to_line_returns()      tr " " "\n"
 
 # Convert input into hexadecimal and a single byte per line.
-to_hex_one_column(){
-	xxd -p -c 1
-}
+to_hex_one_column() { od -An -tx1 | awk '{for(i=1;i<=NF;i++){ print $i }}'; }
 
-# Reverse hexadecimal to original value.
-from_hex(){
-	xxd -p -r
-}
+# One column hexa to one column decimal.
+hex_to_dec() { { echo "obase=10;ibase=16;" ; cat ; } | bc ; }
 
-# Remove non ascii characters, convert "’" to "'", or remove invalid filename characters.
+# Reverse hexadecimal (with space separators) to original value.
+from_hex() { spaces_to_line_returns | uppercase | hex_to_dec | from_dec; }
+
+# Remove non ascii, backslashes and invalid filename characters,
+# convert "’" to "'", "/" to " - ".
 to_ascii(){
-	to_hex_one_column | # Convert input into hexadecimal and a single byte per line.
-		regroup_lines | # Required to easily match multi-byte characters.
-		simple_quote |  # Convert "’" to "'".
-		replace_slashes | # Replace / by ' - ', since it isn't a valid filename character.
+	to_hex_one_column | # Input to hexadecimal, 1-byte representation per line.
+		regroup_lines | # From 1-byte to x-byte lines with space separators.
+		simple_quote |  # From "’" to "'".
+		replace_slashes | # From / to '-'.
 		remove_multibyte_characters | # Remove non ascii values.
-		from_hex # Convert back from hex.
+		remove_backslashes | # Can mess with the script.
+		from_hex # Convert back from hex (x-byte per line, space separator).
 }
 
-process_end_of_songs(){
-	awk -v NONUMBER="$NONUMBER" -v SEPARATOR="$SEPARATOR" '
-
+comp_end_of_tracks() awk -v NONUMBER="$NONUMBER" -v SEPARATOR="$SEPARATOR" '
 	BEGIN {
 		OFS="	"
 	}
@@ -96,10 +98,8 @@ process_end_of_songs(){
 		print timestamp, "END_OF_FILE", title;
 	}
 	'
-}
 
-first_column_to_seconds(){
-	awk '
+first_column_to_seconds() awk '
 	{
 		# from 10:30 to 630
 		n = split ($1, arr, ":")
@@ -120,12 +120,9 @@ first_column_to_seconds(){
 		v = 0;
 	}
 	'
-}
 
 # Get a more usable time representation for the beginning and the end of songs.
-process_time_file(){
-	to_ascii | first_column_to_seconds | process_end_of_songs
-}
+get_timestamps(){ to_ascii | first_column_to_seconds | comp_end_of_tracks; }
 
 run_ffmpeg(){
 	file=$1
@@ -149,7 +146,7 @@ run_ffmpeg(){
 			echo "extracting '$final_title'"
 			;;
 		v2)
-			echo "ffmpeg $LOG_LEVEL $FROM $TO -i $INPUT_FILE '$OUTPUT_FILE'"
+			echo "ffmpeg $LOG_LEVEL $FROM $TO -i $INPUT_FILE $FFOPTS '$OUTPUT_FILE'"
 			;;
 		*)
 			echo "verbosity is not set properly" >&2
@@ -158,15 +155,15 @@ run_ffmpeg(){
 	esac
 
 	if [ "$SIMULATION" = "" ]; then
-		$(< /dev/null ffmpeg $LOG_LEVEL $FROM $TO -i "$INPUT_FILE" "$OUTPUT_FILE")
+		ffmpeg $LOG_LEVEL $FROM $TO -i "$INPUT_FILE" $FFOPTS "$OUTPUT_FILE"
 	fi
 }
 
-rip(){
+extraction(){
 	audio_file="$1"
 	time_file="$2"
 
-	process_time_file < "$time_file" | while read LINE; do
+	get_timestamps < "$time_file" | while read LINE; do
 		track_start=$(echo $LINE | cut -d ' ' -f 1)
 		track_end=$(echo $LINE | cut -d ' ' -f 2)
 		track_title=$(echo $LINE | cut -d ' ' -f 3-)
@@ -175,107 +172,120 @@ rip(){
 			track_end=""
 		fi
 
-		run_ffmpeg "${audio_file}" "${track_start}" "${track_end}" "${track_title}.${FORMAT}"
+		# Input is /dev/null, otherwise subshells will take the output
+		# of "get_timestamps" as input.
+		# Be careful: "while read X" is a dangerous shell design.
+		< /dev/null run_ffmpeg "${audio_file}" \
+			"${track_start}" "${track_end}" \
+			"${track_title}.${FORMAT}"
 	done
 }
 
 usage(){
-	echo "usage: $0 command"
-	echo "command: show <song-list>"
-	echo "command: rip  <single-file-playlist> <song-list>"
-	echo
-	echo "song-list line format example: 1:30 My second track of the playlist"
-	echo "show output format: start end title"
-	echo
-	echo "envvar: SIMULATION, if non empty, do not invoke ffmpeg"
-	echo "envvar: NONUMBER, if equals to 1, do not write song number"
-	echo "envvar: FORMAT [mp3,ogg,opus,…], see the ffmpeg documentation"
-	echo "envvar: SEPARATOR [separator] (default: ' - '), write song number, with this separator"
-	echo "        example with SEPARATOR='_': song names will be 01_song.opus 02_song.opus…"
-	echo "envvar: VERBOSITY [0-3] (default: 1)"
-	echo "        verbosity 0: no output except errors from ffmpeg"
-	echo "        verbosity 1: simple indications on the current track being extracted"
-	echo "        verbosity 2: print actual ffmpeg commands the script currently runs"
+	cat <<END
+Get tracks:
+usage: $0 <single-file-playlist> <song-list>
+
+Debug mode (displays starting and ending times for each song):
+usage: $0 <song-list>
+
+
+Format for <song-list>:
+  0:00 First track
+  1:30 Second track
+
+Environment variables:
+- SIMULATION [empty or not]         do not invoke ffmpeg
+
+- FORMAT [mp3,ogg,opus,…]           see ffmpeg documentation
+- FFOPTS (default: '-c:a copy')     see ffmpeg documentation
+
+- NONUMBER [empty or 1]             do not write song numbers
+- SEPARATOR [separator] (default: ' - ')
+    separator between number and name
+    example with SEPARATOR='_': 01_intro.opus 02_blah.opus…
+
+- HEADERS [empty or 1]             print env params (verbosity, quality, etc.)
+- VERBOSITY [0-3] (default: 1)
+    0: no output except errors from ffmpeg
+    1: simple indications on the current track being extracted
+    2: print actual ffmpeg commands the script currently runs
+END
 }
 
-if [ $# -lt 1 ]; then
-	usage
-	exit 0
+header(){
+	if [ "$HEADERS" = "1" ]; then
+		echo $*
+	fi
+}
+
+warning(){
+	echo "WARNING: $*"
+}
+
+# Default output format is based on the extension of the input audio file.
+if [ $# -eq 2 ]; then
+	DEFAULT_FORMAT="$(echo $1 | awk -F . '{print $NF}')"
+else
+	header "no default FORMAT selected"
 fi
 
-command=$1
-shift
-
 if [ "$FORMAT" = "" ]; then
-	echo "default FORMAT: opus"
-	FORMAT="opus"
+	FORMAT="$DEFAULT_FORMAT"
+	header "default FORMAT: ${FORMAT}"
 else
-	echo "FORMAT: $FORMAT"
+	header "FORMAT: $FORMAT"
+fi
+
+# For unexperienced users, print a warning when input and output formats differ.
+# In case FFOPTS is set, encoding is expected to be handled, drop the warning.
+# Example (remove the get-tracks.sh default behavior, perform re-encoding):
+#   FFOPTS=" "
+if [ "$FFOPTS" = "" ] && [ "$FORMAT" != "$DEFAULT_FORMAT" ]; then
+	warning "input and output formats seem to differ"
+	warning "1. re-encoding may be required (through the FFOPTS envvar)"
+	warning "2. FFOPTS represents ffmpeg options, directly given to ffmpeg"
+	warning '   (default: "-c:a copy" = copy without re-encoding)'
+	warning '   You can put FFOPTS=" " if you want to perform re-encoding.'
 fi
 
 if [ "$VERBOSITY" = "" ]; then
-	echo "default VERBOSITY: 1"
+	header "default VERBOSITY: 1"
 	VERBOSITY=1
 else
-	echo "VERBOSITY level: $VERBOSITY"
+	header "VERBOSITY level: $VERBOSITY"
 fi
 
 if [ "$NONUMBER" = "" ]; then
-	echo "default NONUMBER: disabled"
+	header "default NONUMBER: disabled"
 	NONUMBER=0
 
 	# Assume that there should be a separator.
 	if [ "$SEPARATOR" = "" ]; then
-		echo "default SEPARATOR: ' - '"
+		header "default SEPARATOR: ' - '"
 		SEPARATOR=" - "
 	else
-		echo "SEPARATOR: '$SEPARATOR'"
+		header "SEPARATOR: '$SEPARATOR'"
 	fi
 else
-	echo "NONUMBER: won't prefix tracks"
+	header "NONUMBER: won't prefix tracks"
 	SEPARATOR=""
 fi
 
+if [ "$FFOPTS" != "" ]; then
+	header "FFOPTS envvar is set: ${FFOPTS}."
+else
+	FFOPTS="-c:a copy"
+	header "default FFOPTS: ${FFOPTS}"
+fi
+
 if [ "$SIMULATION" != "" ]; then
-	echo "SIMULATION envvar is set: this is a simulation."
+	header "SIMULATION envvar is set: this is a simulation."
 fi
 
-</dev/null xxd -p >/dev/null 2>/dev/null
-if [ $? -ne 0 ]; then
-	echo "xxd: you don't have an xxd program with '-p' option." 1>&2
-	exit 1
-fi
-
-</dev/null xxd -r >/dev/null 2>/dev/null
-if [ $? -ne 0 ]; then
-	echo "xxd: you don't have an xxd program with '-r' option." 1>&2
-	exit 1
-fi
-
-case "x-${command}" in
-	x-show)
-
-		# Takes the audio file in first parameter
-		if [ $# -ne 1 ]; then
-			echo "Usage: $0 show time-stamps-file" >&2
-			exit 1
-		fi
-
-		process_time_file < "$1"
-		;;
-
-	x-rip)
-
-		# Takes the audio file in first parameter
-		if [ $# -ne 2 ]; then
-			echo "Usage: $0 show music-file time-stamps-file" >&2
-			exit 1
-		fi
-
-		rip "$1" "$2"
-		;;
-
-	*)
-		usage 1>&2
-		exit 1
+case $# in
+	0) usage; exit 0;;
+	1) get_timestamps < "$1";;
+	2) extraction "$1" "$2";;
+	*) usage 1>&2; exit 1;;
 esac