fix: detect mp4 and other common containers in watcher

The watcher only globbed *.mkv, silently ignoring every other source
container. Expand the glob to a list of common input extensions
(mkv, mp4, m4v, mov, avi, ts, m2ts, mts, mpg, mpeg, vob, webm, wmv,
flv). Downstream is unaffected: workdir naming uses filepath.Ext, the
encoder always emits .mkv output, and the metadata regexes are not
end-anchored.

internal/watcher/watcher.go

@@ -13,12 +13,21 @@ import (
 // failureBackoff is how long we skip a file after processFn returned an error
 // for it, provided the file has not been touched since (mtime unchanged). Chosen
 // to be much larger than the polling interval so a permanently-broken input
-// (e.g. video-only mkv producing "no audio streams found") does not spam the
+// (e.g. a video-only file producing "no audio streams found") does not spam the
 // log every tick, but short enough that an operator who fixes the underlying
 // problem by replacing the file sees it picked up promptly on the next stable
 // scan.
 const failureBackoff = 5 * time.Minute
 
+// inputExtensions lists the source container extensions the watcher will pick
+// up. Globbed case-sensitively (matching prior .mkv behavior).
+var inputExtensions = []string{
+	"mkv", "mp4", "m4v", "mov", "avi",
+	"ts", "m2ts", "mts",
+	"mpg", "mpeg", "vob",
+	"webm", "wmv", "flv",
+}
+
 // fileStat is the (mtime, size) pair used to decide whether a file has settled
 // between two consecutive ticks.
 type fileStat struct {
@@ -78,11 +87,15 @@ func (w *Watcher) Start(ctx context.Context, processFn func(context.Context, str
 }
 
 func (w *Watcher) scanAndProcess(ctx context.Context, processFn func(context.Context, string) error) {
-	files, err := filepath.Glob(filepath.Join(w.inputDir, "*.mkv"))
+	var files []string
+	for _, ext := range inputExtensions {
+		matches, err := filepath.Glob(filepath.Join(w.inputDir, "*."+ext))
 		if err != nil {
 			fmt.Printf("Error scanning input directory: %v\n", err)
 			return
 		}
+		files = append(files, matches...)
+	}
 
 	now := time.Now()
 	nextSeen := make(map[string]fileStat, len(files))