[feature] use webp for thumbnails (#3116)

* update to use webp for thumbnails

* bump webp quality up to 40% from 12% (it's a bit different to jpeg quality setting)

* update to use yuva colorspace, and use thumbnail=n=10 to select frame

* fix missing comma in ffmpeg args

* add links to appropriate ffmpeg docs

* update tests

* add file size tests for thumbnails

---------

Co-authored-by: tobi <tobi.smethurst@protonmail.com>

1 files changed, 60 insertions, 7 deletions

diff --git a/internal/media/ffmpeg.go b/internal/media/ffmpeg.go
index add79e26b..6d4c9ac87 100644
--- a/internal/media/ffmpeg.go
+++ b/internal/media/ffmpeg.go
@@ -47,10 +47,21 @@ func ffmpegClearMetadata(ctx context.Context, filepath string, ext string) error
 	// Clear metadata with ffmpeg.
 	if err := ffmpeg(ctx, dirpath,
 		"-loglevel", "error",
+
+		// Input file.
 		"-i", filepath,
+
+		// Drop all metadata.
 		"-map_metadata", "-1",
+
+		// Copy input codecs,
+		// i.e. no transcode.
 		"-codec", "copy",
+
+		// Overwrite.
 		"-y",
+
+		// Output.
 		outpath,
 	); err != nil {
 		return err
@@ -64,23 +75,54 @@ func ffmpegClearMetadata(ctx context.Context, filepath string, ext string) error
 	return nil
 }
 
-// ffmpegGenerateThumb generates a thumbnail jpeg from input media of any type, useful for any media.
+// ffmpegGenerateThumb generates a thumbnail webp from input media of any type, useful for any media.
 func ffmpegGenerateThumb(ctx context.Context, filepath string, width, height int) (string, error) {
+
 	// Get directory from filepath.
 	dirpath := path.Dir(filepath)
 
 	// Generate output frame file path.
-	outpath := filepath + "_thumb.jpg"
+	outpath := filepath + "_thumb.webp"
+
+	// Thumbnail size scaling argument.
+	scale := strconv.Itoa(width) + ":" +
+		strconv.Itoa(height)
 
 	// Generate thumb with ffmpeg.
 	if err := ffmpeg(ctx, dirpath,
 		"-loglevel", "error",
+
+		// Input file.
 		"-i", filepath,
-		"-filter:v", "thumbnail=n=10",
-		"-filter:v", "scale="+strconv.Itoa(width)+":"+strconv.Itoa(height),
-		"-qscale:v", "12", // ~ 70% quality
+
+		// Encode using libwebp.
+		// (NOT as libwebp_anim).
+		"-codec:v", "libwebp",
+
+		// Select thumb from first 10 frames
+		// (thumb filter: https://ffmpeg.org/ffmpeg-filters.html#thumbnail)
+		"-filter:v", "thumbnail=n=10,"+
+
+			// scale to dimensions
+			// (scale filter: https://ffmpeg.org/ffmpeg-filters.html#scale)
+			"scale="+scale+","+
+
+			// YUVA 4:2:0 pixel format
+			// (format filter: https://ffmpeg.org/ffmpeg-filters.html#format)
+			"format=pix_fmts=yuva420p",
+
+		// Only one frame
 		"-frames:v", "1",
+
+		// ~40% webp quality
+		// (codec options: https://ffmpeg.org/ffmpeg-codecs.html#toc-Codec-Options)
+		// (libwebp codec: https://ffmpeg.org/ffmpeg-codecs.html#Options-36)
+		"-qscale:v", "40",
+
+		// Overwrite.
 		"-y",
+
+		// Output.
 		outpath,
 	); err != nil {
 		return "", err
@@ -100,10 +142,21 @@ func ffmpegGenerateStatic(ctx context.Context, filepath string) (string, error)
 	// Generate static with ffmpeg.
 	if err := ffmpeg(ctx, dirpath,
 		"-loglevel", "error",
+
+		// Input file.
 		"-i", filepath,
-		"-codec:v", "png", // specifically NOT 'apng'
-		"-frames:v", "1", // in case animated, only take 1 frame
+
+		// Only first frame.
+		"-frames:v", "1",
+
+		// Encode using png.
+		// (NOT as apng).
+		"-codec:v", "png",
+
+		// Overwrite.
 		"-y",
+
+		// Output.
 		outpath,
 	); err != nil {
 		return "", err