public class GetVedioModel:GetClassInfoModel
    {
        public int blocksize { get; set; }
        public int currentblock { get; set; }
        public int currentblocksize { get; set; }
    }

[HttpPost]
        public async Task<JsonResult> GetVedioBlock(){
            using (var sr = new StreamReader(Request.Body)){
                var json = sr.ReadToEnd();
                GetVedioModel model = JsonConvert.DeserializeObject<GetVedioModel>(json);
                var filePath = MobileDataBaseModel.GetVedioInfo(model);
                if (filePath == null)
                {
                    BaseModel bm = new BaseModel();
                    bm.resualt = false;
                    bm.errorcode = 2;
                    return Json(JsonConvert.SerializeObject(bm));
                }
                Models.MobileModel.BackModel.VedioModel vm = new Models.MobileModel.BackModel.VedioModel();
                vm.current = model.currentblock;
                vm.data = await readFile(model, filePath);
                if(vm.data == null){
                    vm.resualt = false;
                    vm.errorcode = 5;
                }
                else{
                    vm.resualt = true;
                }
                return Json(JsonConvert.SerializeObject(vm));
            }
        }

        private async Task<string> readFile(GetVedioModel model,string path){
            using (FileStream fs = new FileStream(_hostingEnvironment.WebRootPath+path,FileMode.Open,FileAccess.Read,FileShare.Read,model.currentblocksize,true))
            {
                fs.Seek(0,SeekOrigin.Begin);
                byte[] buff = new byte[model.currentblocksize];
                int s = await fs.ReadAsync(buff, (model.currentblock - 1) * model.blocksize, model.currentblocksize);

                if (s > 0)
                {
                    return Encoding.UTF8.GetString(buff);
                }
                return null;
            }
        }