transcode: encoder: avoid format update after open

When the encoder is opened, it cannot change format anymore, and we
cannot change it behind its back.

modules/stream_out/transcode/encoder/encoder.c

@@ -127,15 +127,18 @@ const es_format_t *transcode_encoder_format_out( const transcode_encoder_t *p_en
 void transcode_encoder_update_format_in( transcode_encoder_t *p_enc, const es_format_t *fmt,
                                          const transcode_encoder_config_t *p_cfg )
 {
-    es_format_Clean( &p_enc->p_encoder->fmt_in );
-    es_format_Copy( &p_enc->p_encoder->fmt_in, fmt );
-    switch (fmt->i_cat)
+    if ( !transcode_encoder_opened( p_enc ) )
     {
-        case VIDEO_ES:
-            transcode_encoder_video_set_src(p_enc->p_encoder, &fmt->video, p_cfg);
-            break;
-        default:
-            break;
+        es_format_Clean( &p_enc->p_encoder->fmt_in );
+        es_format_Copy( &p_enc->p_encoder->fmt_in, fmt );
+        switch (fmt->i_cat)
+        {
+            case VIDEO_ES:
+                transcode_encoder_video_set_src(p_enc->p_encoder, &fmt->video, p_cfg);
+                break;
+            default:
+                break;
+        }
     }
 }