feat(output): add no-replacement output mode

Add --output-dir and [processing].output_dir so encoded files can be
written to an existing output directory without replacing, moving, or
deleting originals.

Preserve input paths below the output directory, avoid overwriting
existing outputs with numeric suffixes, and keep --backup-dir compatible
with --output-dir.

Update finalization, backup, and size-report handling so replacement
mode and output-dir mode share the same output path flow.

Document the new mode in the README and man page, add bash completion
for the new option, and expand the size report schema with input and
output paths.

Closes #7.

1 files changed, 60 insertions, 7 deletions

diff --git a/transcode.sh.1 b/transcode.sh.1
index 7093397..7d39eca 100644
--- a/transcode.sh.1
+++ b/transcode.sh.1
@@ -11,7 +11,8 @@ transcode.sh \- batch transcode helper for media files using ffmpeg
 is a batch transcoding wrapper around
 .BR ffmpeg (1)
 that processes one or more media files in place, replacing each with a
-re-encoded version.
+re-encoded version unless no-replacement output mode is enabled with
+.BR \-\-output\-dir .
 .PP
 Encoding parameters are not hard-coded; instead they are supplied by
 .IR presets ,
@@ -153,10 +154,23 @@ Copy originals to \fIDIR\fR before replacing them after successful encoding.
 not. Backups preserve the source file's absolute path below \fIDIR\fR, and
 existing backup files are not overwritten.
 .TP
+.BR \-\-output\-dir " \fIDIR\fR, " \-\-output\-dir= \fIDIR\fR
+Write encoded files below \fIDIR\fR instead of replacing originals.
+\fIDIR\fR must already exist; the script exits with a usage error if it does
+not. Relative input paths are preserved below \fIDIR\fR, while absolute input
+paths are stored without their leading slash. Existing output files are not
+overwritten; numeric suffixes such as
+.B .1
+or
+.B .2
+are appended when needed.
+.TP
 .BR \-l ", " \-\-only\-if\-smaller
-After encoding, replace the original only when the new file is strictly
-smaller. If the transcoded file is larger the temporary file is removed
-and the original is kept unchanged.
+After encoding, keep the new output only when it is strictly smaller than the
+original. In replacement mode, a larger output is removed and the original is
+kept unchanged. In
+.BR \-\-output\-dir
+mode, a larger output is removed and no encoded copy is kept.
 .TP
 .BR \-\-no\-only\-if\-smaller
 After encoding, replace the original also if the new file is bigger.
@@ -275,7 +289,7 @@ which prints every command as it is executed.
 .B XDG_CONFIG_HOME
 Base directory for user configuration. Defaults to
 .BR $HOME/.config .
-.SH BACKUPS
+.SH BACKUPS AND OUTPUT DIRECTORIES
 When
 .BR \-\-backup\-dir
 is used, backups are only created after
@@ -292,6 +306,25 @@ already exists, a numeric suffix such as
 or
 .B .2
 is appended.
+.PP
+When
+.BR \-\-output\-dir
+is used, originals are never replaced, moved, or deleted. Encoded files are
+written below the existing output directory. Relative input paths are preserved
+(for example,
+.I movies/a.mp4
+becomes
+.I encoded/movies/a.mp4
+when the output directory is
+.IR encoded ),
+and absolute input paths are stored without their leading slash. Existing output
+files are not overwritten; numeric suffixes are appended as needed.
+.PP
+.BR \-\-backup\-dir
+and
+.BR \-\-output\-dir
+are compatible. When both are set, the original is copied to the backup
+directory and the encoded file is written to the output directory.
 .SH SIZE REPORT TSV
 When
 .BR \-\-size\-report
@@ -299,7 +332,7 @@ is enabled, the TSV log uses this schema:
 .PP
 .RS
 .nf
-status	filename	original_bytes	new_bytes	saved_pct
+status	input_path	output_path	original_bytes	new_bytes	saved_pct
 .fi
 .RE
 .PP
@@ -309,7 +342,13 @@ The status column is one of
 .BR skipped_larger
 or
 .BR failed .
-Failed rows may leave output-size fields empty when no encoded output exists.
+The
+.B input_path
+field records the original input. The
+.B output_path
+field records the final encoded path for successful encodes and size-based
+skips, and may be empty when no encoded output exists. Failed rows may leave
+output-size fields empty when no encoded output exists.
 .PP
 .SH FILES
 .TP
@@ -461,6 +500,12 @@ encoding and before replacement. Equivalent to
 .BR \-\-backup\-dir .
 CLI \fB--backup-dir\fR takes precedence.
 .TP
+.B [processing] output_dir
+String. Existing directory where encoded files are written without replacing
+originals. Equivalent to
+.BR \-\-output\-dir .
+CLI \fB--output-dir\fR takes precedence.
+.TP
 .B [processing] only_if_smaller
 Boolean. Equivalent to
 .BR \-\-only\-if\-smaller / \-\-no\-only\-if\-smaller .
@@ -547,6 +592,14 @@ transcode.sh \-n \-v my_movie.mkv
 .fi
 .RE
 .PP
+Write encoded copies elsewhere without replacing originals:
+.PP
+.RS
+.nf
+transcode.sh \-\-preset av1 \-\-output\-dir ./encoded video.mp4
+.fi
+.RE
+.PP
 Use a custom preset and only keep the result if it is smaller:
 .PP
 .RS