ffmpeg_opt: dont copy "encoder" metadata unless stream copy is used

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

ffmpeg_opt.c

@@ -2067,6 +2067,8 @@ loop_end:
                 continue;
             ist = input_streams[output_streams[i]->source_index];
             av_dict_copy(&output_streams[i]->st->metadata, ist->st->metadata, AV_DICT_DONT_OVERWRITE);
+            if (!output_streams[i]->stream_copy)
+                av_dict_set(&output_streams[i]->st->metadata, "encoder", NULL, 0);
         }
 
     /* process manually set metadata */