新增 Mjpegplayer 用来播放 Web 流

SHH.Contracts.Grpc/Images/VideoPayload.cs

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+using Newtonsoft.Json;
+// 注意：如果不想依赖 Newtonsoft，也可以用 System.Text.Json，但 Newtonsoft 在 Std 2.0 中兼容性更好
+
+namespace SHH.Contracts
+{
+    /// <summary>
+    /// 视频数据传输契约（纯净版 POCO）
+    /// </summary>
+    public class VideoPayload
+    {
+        /// <summary>
+        /// 构造函数
+        /// </summary>
+        public VideoPayload()
+        {
+            SubscriberIds = new List<string>(16);
+            Diagnostics = new Dictionary<string, object>(4);
+        }
+
+        #region --- 1. 元数据 (Metadata) ---
+
+        public string CameraId { get; set; } = string.Empty;
+
+        /// <summary>采集时间戳 (Unix 毫秒)</summary>
+        public long CaptureTimestamp { get; set; }
+
+        /// <summary>分发时间戳 (Unix 毫秒)</summary>
+        public long DispatchTimestamp { get; set; }
+
+        /// <summary>原始图像宽度</summary>
+        public int OriginalWidth { get; set; }
+
+        /// <summary>原始图像高度</summary>
+        public int OriginalHeight { get; set; }
+
+        /// <summary>目标图像宽度</summary>
+        public int TargetWidth { get; set; }
+
+        /// <summary>目标图像高度</summary>
+        public int TargetHeight { get; set; }
+
+        /// <summary>订阅Ids</summary>
+        public List<string> SubscriberIds { get; set; }
+
+        /// <summary>诊断信息</summary>
+        public Dictionary<string, object> Diagnostics { get; set; }
+
+        /// <summary>
+        /// 指示标志：是否存在原始图
+        /// </summary>
+        public bool HasOriginalImage { get; set; }
+
+        /// <summary>
+        /// 指示标志：是否存在处理图
+        /// </summary>
+        public bool HasTargetImage { get; set; }
+
+        #endregion
+
+        #region --- 2. 二进制数据 (Binary) ---
+
+        // 标记 JsonIgnore，防止被错误序列化
+        [JsonIgnore]
+        public byte[]? OriginalImageBytes { get; set; }
+
+        [JsonIgnore]
+        public byte[]? TargetImageBytes { get; set; }
+
+        #endregion
+
+        #region --- 3. 辅助方法 (仅保留 JSON 逻辑) ---
+
+        /// <summary>
+        /// 获取纯元数据的 JSON 字符串
+        /// </summary>
+        public string GetMetadataJson()
+        {
+            // 在序列化前自动更新标志位，防止逻辑不同步
+            HasOriginalImage = (OriginalImageBytes != null && OriginalImageBytes.Length > 0);
+            HasTargetImage = (TargetImageBytes != null && TargetImageBytes.Length > 0);
+
+            return JsonConvert.SerializeObject(this);
+        }
+
+        public static VideoPayload? FromMetadataJson(string json)
+        {
+            return JsonConvert.DeserializeObject<VideoPayload>(json);
+        }
+
+        #endregion
+    }
+}