qtdemux works incorrectly with opus codecs.

Hi all, I am facing this problem while working on my project I create audio stream file with **qtmux **and stream it but qtdemux can't play it (caps of source pad always return NULL), and this file I can play it by vlc. I use gstreamer 1.16.2

This is pipeline to create file.

htdung@CaCs:~$ gst-launch-1.0 -e audiotestsrc num-buffers=100 ! opusenc ! qtmux ! filesink location=tmp.qt
 

This is pipeline to stream audio.

    htdung@CaCs:~$ gst-launch-1.0 filesrc location=tmp.qt ! qtdemux ! rtpopuspay pt=96 ! udpsink host=127.0.0.1 port=10000 
    Setting pipeline to PAUSED ...
    Pipeline is PREROLLING ...

    (gst-launch-1.0:6036): GStreamer-CRITICAL **: 14:25:01.954: gst_caps_get_structure: assertion 'GST_IS_CAPS (caps)' failed

    (gst-launch-1.0:6036): GStreamer-CRITICAL **: 14:25:01.954: gst_structure_get_int: assertion 'structure != NULL' failed
    ERROR: from element /GstPipeline:pipeline0/GstRtpOPUSPay:rtpopuspay0: GStreamer error: negotiation problem.
    Additional debug info:
    gstrtpbasepayload.c(712): gst_rtp_base_payload_chain (): /GstPipeline:pipeline0/GstRtpOPUSPay:rtpopuspay0:
    No input format was negotiated, i.e. no caps event was received. Perhaps you need a parser or typefind element before the payloader
    ERROR: pipeline doesn't want to preroll.
    Setting pipeline to NULL ...
    Freeing pipeline ...

Note: But if I try to create the file with mp4mux qtdemux works fine. I tried to find the source code, it seems that it could be caused by hard code

        case FOURCC_opus:
        {
          const guint8 *opus_data;
          guint8 *channel_mapping = NULL;
          guint32 rate;
          guint8 channels;
          guint8 channel_mapping_family;
          guint8 stream_count;
          guint8 coupled_count;
          guint8 i;

          opus_data = stsd_entry_data;

          channels = GST_READ_UINT8 (opus_data + 45);
          rate = GST_READ_UINT32_LE (opus_data + 48);
          channel_mapping_family = GST_READ_UINT8 (opus_data + 54);
          stream_count = GST_READ_UINT8 (opus_data + 55);
          coupled_count = GST_READ_UINT8 (opus_data + 56);

          if (channels > 0) {
            channel_mapping = g_malloc (channels * sizeof (guint8));
            for (i = 0; i < channels; i++)
              channel_mapping[i] = GST_READ_UINT8 (opus_data + i + 57);
          }

          entry->caps = gst_codec_utils_opus_create_caps (rate, channels,
              channel_mapping_family, stream_count, coupled_count,
              channel_mapping);
          break;
        }
        default:
          break;
      }