HarmonyOS AVDexmuer无法获取视频时长

照着这里的文档：https://developer.huawei.com/consumer/cn/doc/harmonyos-guides-V5/audio-video-demuxer-V5

下面的duration输出为0：

for (uint32_t index = 0; index < track_count; ++index) {
  OH_AVFormat *track_format = OH_AVSource_GetTrackFormat(av_source_, index);
  if (!track_format) {
    XLOG_ERROR("OH_AVSource_GetTrackFormat failed");
    if (error) {
      *error = MAKE_ERROR(kErrorDomainDecode, kErrorCodeGetTrackFormatFailed);
    }
    return;
  }
  OH_AVFormat_GetIntValue(track_format, OH_MD_KEY_TRACK_TYPE, &track_type);
  OH_MediaType media_type = static_cast<OH_MediaType>(track_type);
  if (media_type == OH_MediaType::MEDIA_TYPE_VID) {
    {
      int64_t duraion;
      OH_AVFormat_GetLongValue(track_format, OH_MD_KEY_DURATION, &duraion);
      XLOG_INFO("video duration: %lld", duraion);
    }
    {
      int32_t duraion;
      OH_AVFormat_GetIntValue(track_format, OH_MD_KEY_DURATION, &duraion);
      XLOG_INFO("video duration: %d", duraion);
    }
    {
      double duration;
      OH_AVFormat_GetDoubleValue(track_format, OH_MD_KEY_DURATION, &duration);
      XLOG_INFO("video duration: %f", duration);
    }
  } else {
    {
      int64_t duraion;
      OH_AVFormat_GetLongValue(track_format, OH_MD_KEY_DURATION, &duraion);
      XLOG_INFO("audio duration: %lld", duraion);
    }
    {
      int32_t duraion;
      OH_AVFormat_GetIntValue(track_format, OH_MD_KEY_DURATION, &duraion);
      XLOG_INFO("audio duration: %d", duraion);
    }
    {
      double duration;
      OH_AVFormat_GetDoubleValue(track_format, OH_MD_KEY_DURATION, &duration);
      XLOG_INFO("video duration: %f", duration);
    }
  }
}