fix: improve input validation and error reporting

Validate the nice value is an integer in [-20, 19] at startup rather
than letting nice(1) fail with a cryptic error at encode time.

In encode_one, move the "Processing" message after the empty-string
guard so it is not printed for blank lines, include the filename in the
"Not found" error, and add a readability check so unreadable files are
rejected with a clear message before ffprobe is invoked.

Validate that the encode file (-f) exists before entering the read
loop, exiting with a usage error rather than a silent empty run.

1 files changed, 16 insertions, 2 deletions

diff --git a/transcode.sh b/transcode.sh
index 15dba25..500111d 100755
--- a/transcode.sh
+++ b/transcode.sh
@@ -557,6 +557,11 @@ if [[ $SAVING -eq 1 ]]; then
   }
 fi
 
+if [[ ! "$NICE_VALUE" =~ ^-?[0-9]+$ ]] || ((NICE_VALUE < -20 || NICE_VALUE > 19)); then
+  error "Invalid nice value (must be an integer between -20 and 19):" "$NICE_VALUE"
+  exit $EXIT_USAGE_ERROR
+fi
+
 # Remove temporary output files created during encoding.
 # Registered via trap EXIT so it runs on normal exit and on failures
 # shellcheck disable=SC2329
@@ -584,11 +589,16 @@ trap cleanup EXIT
 #   EXIT_OK on success or if skipped; EXIT_RUNTIME_FAILURE on failure.
 encode_one() {
   local file="$1"
-  msg "Processing:" "$file"
 
   [[ -z "$file" ]] && return $EXIT_OK
+
+  msg "Processing:" "$file"
   [[ ! -f "$file" ]] && {
-    error "Not found"
+    error "Not found:" "$file"
+    return $EXIT_RUNTIME_FAILURE
+  }
+  [[ ! -r "$file" ]] && {
+    error "File is not readable:" "$file"
     return $EXIT_RUNTIME_FAILURE
   }
 
@@ -752,6 +762,10 @@ encode_one() {
 
 STATUS=$EXIT_OK
 if [[ -n $ENCODE_FILE ]]; then
+  [[ -f "$ENCODE_FILE" ]] || {
+    error "Encode file not found:" "$ENCODE_FILE"
+    exit $EXIT_USAGE_ERROR
+  }
   while IFS= read -r file || [[ -n "$file" ]]; do
     encode_one "$file" || STATUS=$EXIT_RUNTIME_FAILURE
   done <"$ENCODE_FILE"