ffmpegencoder: set avg_frame_rate

app/codec/ffmpeg/ffmpegencoder.cpp

@@ -696,7 +696,6 @@ bool FFmpegEncoder::InitializeStream(AVMediaType type, AVStream** stream_ptr, AV
     codec_ctx->time_base = params().video_params().frame_rate_as_time_base().toAVRational();
     codec_ctx->framerate = params().video_params().frame_rate().toAVRational();
     codec_ctx->pix_fmt = av_get_pix_fmt(params().video_pix_fmt().toUtf8());
-    codec_ctx->gop_size = 12;
 
     if (params().video_params().interlacing() != VideoParams::kInterlaceNone) {
       // FIXME: I actually don't know what these flags do, the documentation helpfully doesn't
@@ -820,6 +819,10 @@ bool FFmpegEncoder::SetupCodecContext(AVStream* stream, AVCodecContext* codec_ct
     return false;
   }
 
+  if (codec->type == AVMEDIA_TYPE_VIDEO) {
+    stream->avg_frame_rate = codec_ctx->framerate;
+  }
+
   return true;
 }