refactor: use io.Reader instead of custom method

algo/common/common.go

@@ -1,13 +1,13 @@
 package common
 
-import "context"
+import (
+	"context"
+	"io"
+)
 
 type Decoder interface {
 	Validate() error
-	Decode() error
-	GetAudioData() []byte
-	GetAudioExt() string
-	GetMeta() Meta
+	io.Reader
 }
 
 type CoverImageGetter interface {
@@ -19,3 +19,7 @@ type Meta interface {
 	GetTitle() string
 	GetAlbum() string
 }
+
+type StreamDecoder interface {
+	Decrypt(buf []byte, offset int)
+}