ffplay: provide some feedback in case the codec cannot be set

ffplay.c

@@ -2300,6 +2300,7 @@ static int stream_component_open(VideoState *is, int stream_index)
     AVFormatContext *ic = is->ic;
     AVCodecContext *avctx;
     AVCodec *codec;
+    const char *forced_codec_name = NULL;
     AVDictionary *opts;
     AVDictionaryEntry *t = NULL;
 
@@ -2310,12 +2311,17 @@ static int stream_component_open(VideoState *is, int stream_index)
     codec = avcodec_find_decoder(avctx->codec_id);
 
     switch(avctx->codec_type){
-        case AVMEDIA_TYPE_AUDIO   : is->last_audio_stream    = stream_index; if(audio_codec_name   ) codec= avcodec_find_decoder_by_name(   audio_codec_name); break;
-        case AVMEDIA_TYPE_SUBTITLE: is->last_subtitle_stream = stream_index; if(subtitle_codec_name) codec= avcodec_find_decoder_by_name(subtitle_codec_name); break;
-        case AVMEDIA_TYPE_VIDEO   : is->last_video_stream    = stream_index; if(video_codec_name   ) codec= avcodec_find_decoder_by_name(   video_codec_name); break;
-    }
-    if (!codec)
+        case AVMEDIA_TYPE_AUDIO   : is->last_audio_stream    = stream_index; forced_codec_name =    audio_codec_name; break;
+        case AVMEDIA_TYPE_SUBTITLE: is->last_subtitle_stream = stream_index; forced_codec_name = subtitle_codec_name; break;
+        case AVMEDIA_TYPE_VIDEO   : is->last_video_stream    = stream_index; forced_codec_name =    video_codec_name; break;
+    }
+    if (forced_codec_name)
+        codec = avcodec_find_decoder_by_name(forced_codec_name);
+    if (!codec) {
+        if (forced_codec_name) fprintf(stderr, "No codec could be found with name '%s'\n", forced_codec_name);
+        else                   fprintf(stderr, "No codec could be found with id %d\n", avctx->codec_id);
         return -1;
+    }
 
     avctx->codec_id = codec->id;
     avctx->workaround_bugs   = workaround_bugs;