Made it possible for each encoder to add its own parameters.

Added preset option for libx264.

encoder/libx264/encoder.go

@@ -1,16 +1,38 @@
 package libx264
 
-import encoder2 "git.kor-elf.net/kor-elf/gui-for-ffmpeg/encoder"
+import (
+	"errors"
+	encoder2 "git.kor-elf.net/kor-elf/gui-for-ffmpeg/encoder"
+)
 
-type encoder struct {
+var Presets = []string{
+	"ultrafast",
+	"superfast",
+	"veryfast",
+	"faster",
+	"fast",
+	"medium",
+	"slow",
+	"slower",
+	"veryslow",
+	"placebo",
 }
 
 func NewEncoder() encoder2.EncoderContract {
-	return &encoder{}
-}
+	parameters := map[string]encoder2.ParameterContract{
+		"preset": newParameterPreset(),
+	}
+	getParams := func(parameters map[string]encoder2.ParameterContract) []string {
+		params := []string{"-c:v", "libx264"}
 
-func (e encoder) GetParams() []string {
-	return []string{"-c:v", "libx264"}
+		if parameters["preset"] != nil && parameters["preset"].IsEnabled() {
+			params = append(params, "-preset", parameters["preset"].Get())
+		}
+
+		return params
+	}
+
+	return encoder2.NewEncoder("libx264", parameters, getParams)
 }
 
 func NewData() encoder2.EncoderDataContract {
@@ -19,3 +41,16 @@ func NewData() encoder2.EncoderDataContract {
 	fileType := encoder2.FileType(encoder2.Video)
 	return encoder2.NewData(title, formats, fileType, NewEncoder)
 }
+
+func newParameterPreset() encoder2.ParameterContract {
+	setParameter := func(s string) (string, error) {
+		for _, value := range Presets {
+			if value == s {
+				return value, nil
+			}
+		}
+
+		return "", errors.New("preset not found")
+	}
+	return encoder2.NewParameter("preset", false, "medium", setParameter)
+}