Do not automatically map subtitles if the decoder and encoder properties are different.

Fixes ticket #3819.

ffmpeg_opt.c

@@ -1870,8 +1870,27 @@ static int open_output_file(OptionsContext *o, const char *filename)
         if (!o->subtitle_disable && (avcodec_find_encoder(oc->oformat->subtitle_codec) || subtitle_codec_name)) {
             for (i = 0; i < nb_input_streams; i++)
                 if (input_streams[i]->st->codec->codec_type == AVMEDIA_TYPE_SUBTITLE) {
-                    new_subtitle_stream(o, oc, i);
-                    break;
+                    AVCodecDescriptor const *input_descriptor =
+                        avcodec_descriptor_get(input_streams[i]->st->codec->codec_id);
+                    AVCodecDescriptor const *output_descriptor = NULL;
+                    AVCodec const *output_codec =
+                        avcodec_find_encoder(oc->oformat->subtitle_codec);
+                    int input_props = 0, output_props = 0;
+                    if (output_codec)
+                        output_descriptor = avcodec_descriptor_get(output_codec->id);
+                    if (input_descriptor)
+                        input_props = input_descriptor->props & (AV_CODEC_PROP_TEXT_SUB | AV_CODEC_PROP_BITMAP_SUB);
+                    if (output_descriptor)
+                        output_props = output_descriptor->props & (AV_CODEC_PROP_TEXT_SUB | AV_CODEC_PROP_BITMAP_SUB);
+                    if (subtitle_codec_name ||
+                        input_props & output_props ||
+                        // Map dvb teletext which has neither property to any output subtitle encoder
+                        input_descriptor && output_descriptor &&
+                        (!input_descriptor->props ||
+                         !output_descriptor->props)) {
+                        new_subtitle_stream(o, oc, i);
+                        break;
+                    }
                 }
         }
         /* do something with data? */