media_encoder: enable libopus FEC encoding

Adds a function to initialize the opus encoder with FEC support and a
default packet loss of 10%.
In future iterations, the default value should be set to 0 and the
packet loss adapted accordingly to RTCP control packets.

Issue: #5156
Change-Id: I79b9c5e38ed388466d7b71a394f961d2ff9b001f

src/media/media_encoder.cpp

@@ -761,6 +761,13 @@ MediaEncoder::initCodec(AVMediaType mediaType, AVCodecID avcodecId, uint64_t br)
         }
     }
 
+    /* Enable libopus FEC encoding support */
+    if (mediaType == AVMEDIA_TYPE_AUDIO) {
+        if (avcodecId == AV_CODEC_ID_OPUS) {
+            initOpus(encoderCtx);
+        }
+    }
+
     /* let x264 preset override our encoder settings */
     if (avcodecId == AV_CODEC_ID_H264) {
         auto profileLevelId = libav_utils::getDictValue(options_, "parameters");
@@ -951,6 +958,15 @@ MediaEncoder::initH263(AVCodecContext* encoderCtx, uint64_t br)
     JAMI_DBG("H263 encoder setup: maxrate=%lu, bufsize=%lu", maxBitrate, bufSize);
 }
 
+void
+MediaEncoder::initOpus(AVCodecContext* encoderCtx)
+{
+    int ret;
+    // Enable FEC support by default with 10% packet loss
+    av_opt_set_int(encoderCtx, "enable_fec", 1, AV_OPT_SEARCH_CHILDREN);
+    av_opt_set_int(encoderCtx, "packet_loss", 10, AV_OPT_SEARCH_CHILDREN);
+}
+
 void
 MediaEncoder::initAccel(AVCodecContext* encoderCtx, uint64_t br)
 {

src/media/media_encoder.h

@@ -132,6 +132,7 @@ private:
     void initVP8(AVCodecContext* encoderCtx, uint64_t br);
     void initMPEG4(AVCodecContext* encoderCtx, uint64_t br);
     void initH263(AVCodecContext* encoderCtx, uint64_t br);
+    void initOpus(AVCodecContext* encoderCtx);
     bool isDynBitrateSupported(AVCodecID codecid);
     void initAccel(AVCodecContext* encoderCtx, uint64_t br);
     int getHWFrame(const std::shared_ptr<VideoFrame>& input, std::shared_ptr<VideoFrame>& output);