harden ffmpeg pipeline failure handling and stream mapping

internal/app/app.go

@@ -2,7 +2,9 @@ package app
 
 import (
 	"context"
+	"errors"
 	"fmt"
+	"os/exec"
 	"path/filepath"
 	"regexp"
 	"sort"
@@ -903,6 +905,10 @@ func (m *Main) ripTrack(ctx context.Context, p provider.Client, source, id, fall
 		}
 	}
 	if err = m.Tagger.TagFLAC(outPath, tagMeta, coverPath); err != nil {
+		if isFFmpegMissingError(err) {
+			_ = m.Store.MarkFailed(ctx, source, "track", id)
+			return fmt.Errorf("id=%s title=%q tag: %w", id, title, err)
+		}
 		m.logf("warning: tag failed for %s: %v\n", filepath.Base(outPath), err)
 	}
 
@@ -1342,3 +1348,13 @@ func applyPlaylistMetadataOverrides(meta map[string]any, cfg config.MetadataConf
 	}
 	artist["name"] = "Various Artists"
 }
+
+func isFFmpegMissingError(err error) bool {
+	if err == nil {
+		return false
+	}
+	if errors.Is(err, exec.ErrNotFound) {
+		return true
+	}
+	return strings.Contains(strings.ToLower(err.Error()), "ffmpeg not found")
+}