media_decoder: enable libopus FEC by default

By default, sets the option to use FEC decoding with libopus when
preparing the decoder context.

Issue: #5155
Change-Id: Icc9dcbbd9df3f538eb2da794e2ff9b6a0380bdc2

src/media/media_decoder.cpp

@@ -526,6 +526,11 @@ MediaDecoder::prepareDecoderContext()
         if (decoderCtx_->framerate.num == 0 || decoderCtx_->framerate.den == 0)
             decoderCtx_->framerate = {30, 1};
     }
+    if (avStream_->codecpar->codec_type == AVMEDIA_TYPE_AUDIO) {
+        if (decoderCtx_->codec_id == AV_CODEC_ID_OPUS) {
+            av_opt_set_int(decoderCtx_, "decode_fec", 1, AV_OPT_SEARCH_CHILDREN);
+        }
+    }
     return 0;
 }