feat(hugomanager): improve shrink-audio-files

1. Add more logging
2. Handle `m4a` files better

Author: ashishb

src/wp2hugo/cmd/hugomanager/cmd/shrink_audio.go

@@ -51,10 +51,13 @@ func shrinkAudioFiles(ctx context.Context, hugoDir string, maxBitRate int, updat
 			return err
 		}
 
-		if *bitrate <= maxBitRate {
+		// If you shrink a file to 48kbps, sometimes the resulting bitrate is 64kbps,
+		// so we give a 33% buffer to avoid unnecessary re-processing
+		if *bitrate <= (maxBitRate * 4 / 3) {
 			log.Trace().
 				Str("filePath", filePath).
 				Int("bitrate", *bitrate).
+				Int("maxBitRate", maxBitRate).
 				Msg("Audio file within bitrate limits, skipping")
 			return nil
 		}

src/wp2hugo/internal/hugomanager/mediafileshrinker/audio_file_helper.go

@@ -11,6 +11,7 @@ import (
 	"github.com/ashishb/wp2hugo/src/wp2hugo/internal/hugomanager/imageshrinker"
 	"github.com/barasher/go-exiftool"
 	"github.com/rs/zerolog/log"
+	"github.com/samber/lo"
 )
 
 func GetAudioBitrate(filePath string) (*int, error) {
@@ -33,18 +34,28 @@ func GetAudioBitrate(filePath string) (*int, error) {
 
 	bitRateAny, ok := metadata.Fields["AudioBitrate"]
 	if !ok {
-		return nil, fmt.Errorf("AudioBitrate field not found in metadata for file: %s", filePath)
+		bitrateAny2, ok2 := metadata.Fields["AvgBitrate"] // For .m4a files
+		if ok2 {
+			bitRateAny = bitrateAny2
+		} else {
+			log.Debug().
+				Str("filePath", filePath).
+				Interface("metadataFields", lo.Keys(metadata.Fields)).
+				Msg("Available metadata fields")
+			return nil, fmt.Errorf("AudioBitrate field not found in metadata for file: %s", filePath)
+		}
 	}
 
 	bitRateStr := fmt.Sprintf("%v", bitRateAny)
 	bitRateStr = strings.ReplaceAll(bitRateStr, " kbps", "000")
 	bitRateStr = strings.ReplaceAll(bitRateStr, " mbps", "000000")
-	bitRateInt, err := strconv.Atoi(bitRateStr)
+	// Average bit rate is usually in bps, so we need to parse as a float
+	bitRateFloat, err := strconv.ParseFloat(bitRateStr, 64)
 	if err != nil {
 		return nil, fmt.Errorf("unable to convert bitrate to int for file %s: %w", filePath, err)
 	}
 
-	return &bitRateInt, nil
+	return lo.ToPtr(int(bitRateFloat)), nil
 }
 
 // ReduceAudioBitrate processes a media file to reduce its audio bitrate
@@ -77,11 +88,16 @@ func ReduceAudioBitrate(ctx context.Context, inputFile string, outputFile string
 		return fmt.Errorf("FFmpeg failed: %w\nOutput: %s", err, output)
 	}
 
+	originalSize := imageshrinker.GetFileSize(inputFile)
+	newSize := imageshrinker.GetFileSize(outputFile)
+	shrunkPct := 100.0 * (float64(originalSize-newSize) / float64(originalSize))
+
 	log.Info().
 		Str("inputFile", inputFile).
 		Str("outputFile", outputFile).
-		Int64("inputFileSize", imageshrinker.GetFileSize(inputFile)).
-		Int64("outputFileSize", imageshrinker.GetFileSize(outputFile)).
+		Int64("inputFileSize", originalSize).
+		Int64("outputFileSize", newSize).
+		Str("shrinkBy", fmt.Sprintf("%.0f%%", shrunkPct)).
 		Str("bitrate", fmt.Sprintf("%dkbps", bitRate/1000)).
 		Msg("Audio bitrate reduction completed successfully")
 	return nil