Libraries which did not open a file must not sync them.

... or do any system-level stuff with the files, because they do not
know the specifics, for example where, on which file system or network
device the files are being stored. Only the file creator knows that.

encoder.go

@@ -6,7 +6,6 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"os"
 	"reflect"
 
 	"github.com/go-audio/audio"
@@ -316,9 +315,5 @@ func (e *Encoder) Close() error {
 	if _, err := e.w.Seek(0, 2); err != nil {
 		return err
 	}
-	switch e.w.(type) {
-	case *os.File:
-		return e.w.(*os.File).Sync()
-	}
 	return nil
 }