video: add extra ffmpeg magic for aspect-scaling

video.go

@@ -2,18 +2,25 @@ package thumbnail
 
 import (
 	"bytes"
+	"fmt"
 	"io"
 	"os/exec"
 )
 
 func (this *Thumbnailer) RenderScaledFfmpeg(absPath string) ([]byte, error) {
 
+	scaleCmd := fmt.Sprintf(
+		`thumbnail,scale='if(gt(a,%d/%d),%d,-1)':'if(gt(a,%d/%d),-1,%d)'`,
+		this.Height, this.Width, this.Height,
+		this.Height, this.Width, this.Width,
+	)
+
 	cmd := exec.Command(
 		"ffmpeg",
 		"-loglevel", "0",
 		"-an",
 		"-i", absPath,
-		"-vf", "thumbnail,scale=100:100",
+		"-vf", scaleCmd,
 		"-frames:v", "1",
 		"-f", "image2pipe",
 		"-c:v", "png",