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

Added preset option for libx264.

encoder/encoder.go

@@ -1,7 +1,20 @@
 package encoder
 
+import "errors"
+
 type EncoderContract interface {
+	GetName() string
 	GetParams() []string
+	GetParameter(name string) (ParameterContract, error)
+}
+
+type ParameterContract interface {
+	GetName() string
+	Set(string) error
+	Get() string
+	IsEnabled() bool
+	SetEnable()
+	SetDisable()
 }
 
 type EncoderDataContract interface {
@@ -77,3 +90,80 @@ func GetListFileType() []FileTypeContract {
 		FileType(Image),
 	}
 }
+
+type Encoder struct {
+	name       string
+	parameters map[string]ParameterContract
+	getParams  func(parameters map[string]ParameterContract) []string
+}
+
+func NewEncoder(name string, parameters map[string]ParameterContract, getParams func(parameters map[string]ParameterContract) []string) *Encoder {
+	return &Encoder{
+		name:       name,
+		parameters: parameters,
+		getParams:  getParams,
+	}
+}
+
+func (e *Encoder) GetName() string {
+	return e.name
+}
+
+func (e *Encoder) GetParams() []string {
+	return e.getParams(e.parameters)
+}
+
+func (e *Encoder) GetParameter(name string) (ParameterContract, error) {
+	if e.parameters[name] == nil {
+		return nil, errors.New("parameter not found")
+	}
+
+	return e.parameters[name], nil
+}
+
+type Parameter struct {
+	name         string
+	isEnabled    bool
+	parameter    string
+	setParameter func(string) (string, error)
+}
+
+func NewParameter(name string, isEnabled bool, defaultParameter string, setParameter func(string) (string, error)) *Parameter {
+	return &Parameter{
+		name:         name,
+		isEnabled:    isEnabled,
+		parameter:    defaultParameter,
+		setParameter: setParameter,
+	}
+}
+
+func (p *Parameter) GetName() string {
+	return p.name
+}
+
+func (p *Parameter) Set(s string) (err error) {
+	if p.setParameter != nil {
+		s, err = p.setParameter(s)
+		if err != nil {
+			return err
+		}
+	}
+	p.parameter = s
+	return nil
+}
+
+func (p *Parameter) Get() string {
+	return p.parameter
+}
+
+func (p *Parameter) IsEnabled() bool {
+	return p.isEnabled
+}
+
+func (p *Parameter) SetEnable() {
+	p.isEnabled = true
+}
+
+func (p *Parameter) SetDisable() {
+	p.isEnabled = false
+}