Create a thumbnails sprite api

transcoder/src/extract.go

@@ -49,8 +49,8 @@ func (e *Extractor) RunExtractor(path string, sha string, subs *[]Subtitle) <-ch
 	e.lock.Unlock()
 
 	go func() {
-		attachment_path := fmt.Sprintf("%s/%s/att/", GetMetadataPath(), sha)
-		subs_path := fmt.Sprintf("%s/%s/sub/", GetMetadataPath(), sha)
+		attachment_path := fmt.Sprintf("%s/%s/att", GetMetadataPath(), sha)
+		subs_path := fmt.Sprintf("%s/%s/sub", GetMetadataPath(), sha)
 		os.MkdirAll(attachment_path, 0o644)
 		os.MkdirAll(subs_path, 0o755)
 

transcoder/src/thumbnails.go

@@ -0,0 +1,92 @@
+package src
+
+import (
+	"fmt"
+	"image"
+	"image/color"
+	"log"
+	"math"
+	"os"
+
+	"github.com/disintegration/imaging"
+	"gitlab.com/opennota/screengen"
+)
+
+// We want to have a thumbnail every ${interval} seconds.
+var default_interval = 10
+
+func ExtractThumbnail(path string) (string, error) {
+	ret, err := GetInfo(path)
+	if err != nil {
+		return "", err
+	}
+	out := fmt.Sprintf("%s/%s", GetMetadataPath(), ret.Sha)
+	sprite_path := fmt.Sprintf("%s/sprite.png", out)
+	vtt_path := fmt.Sprintf("%s/sprite.vtt", out)
+
+	gen, err := screengen.NewGenerator(path)
+	if err != nil {
+		log.Printf("Error reading video file: %v", err)
+		return "", err
+	}
+	defer gen.Close()
+
+	gen.Fast = true
+
+	// truncate duration to full seconds
+	// this prevents empty/black images when the movie is some milliseconds longer
+	// ffmpeg then sometimes takes a black screenshot AFTER the movie finished for some reason
+	duration := 1000 * (int(gen.Duration) / 1000)
+	var numcaps, interval int
+	if default_interval < duration {
+		numcaps = duration / default_interval * 1000
+		interval = default_interval
+	} else {
+		numcaps = duration / 10
+		interval = duration / numcaps
+	}
+	columns := int(math.Sqrt(float64(numcaps)))
+	rows := int(math.Ceil(float64(numcaps) / float64(columns)))
+
+	width := gen.Width()
+	height := gen.Height()
+
+	sprite := imaging.New(width*columns, height*rows, color.Black)
+	vtt := "WEBVTT\n\n"
+
+	ts := 0
+	for i := 0; i < numcaps; i++ {
+		img, err := gen.Image(int64(ts))
+		if err != nil {
+			log.Printf("Could not generate screenshot %s", err)
+			return "", err
+		}
+
+		// TODO: resize image
+
+		x := i % width
+		y := i / width
+		sprite = imaging.Paste(sprite, img, image.Pt(x, y))
+
+		timestamps := ts
+		ts += interval
+		vtt += fmt.Sprintf(
+			"%s --> %s\n%s#xywh=%d,%d,%d,%d\n\n",
+			tsToVttTime(timestamps),
+			tsToVttTime(ts),
+			name,
+			x,
+			y,
+			width,
+			height,
+		)
+	}
+
+	os.WriteFile(vtt_path, []byte(vtt), 0o644)
+	imaging.Save(sprite, sprite_path)
+	return out, nil
+}
+
+func tsToVttTime(ts int) string {
+	return fmt.Sprintf("%02d:%02d:%02d.000", ts/3600, ts/60, ts%60)
+}