diff --git a/scripts/iib/fastapi_video.py b/scripts/iib/fastapi_video.py
index bd2ade1..fa4519e 100644
--- a/scripts/iib/fastapi_video.py
+++ b/scripts/iib/fastapi_video.py
@@ -1,48 +1,89 @@
 import os
-from typing import BinaryIO
+from typing import BinaryIO, Dict, Tuple
 
-from fastapi import FastAPI, HTTPException, Request, status
+from fastapi import HTTPException, Request, status
 from fastapi.responses import StreamingResponse
 from scripts.iib.tool import get_video_type
 
-video_file_handler = {}
+video_file_handler: Dict[str, "BinaryIO"] = {}
 
 def close_video_file_reader(path):
     if not get_video_type(path):
         return
     try:
-        video_file_handler[path].close()
+        f = video_file_handler.get(path)
+        if f is not None:
+            f.close()
     except Exception as e:
         print(f"close file error: {e}")
     
 
 def send_bytes_range_requests(
-    file_path, start: int, end: int, chunk_size: int = 10_000
+    file_path: str,
+    start: int,
+    end: int,
+    chunk_size: int = 1024 * 1024,
 ):
     """Send a file in chunks using Range Requests specification RFC7233
 
     `start` and `end` parameters are inclusive due to specification
     """
-    with open(file_path, mode="rb") as f:
+    f = None
+    try:
+        # Larger chunk size improves throughput for large video files.
+        f = open(file_path, mode="rb")
         video_file_handler[file_path] = f
         f.seek(start)
         while (pos := f.tell()) <= end:
             read_size = min(chunk_size, end + 1 - pos)
-            yield f.read(read_size)
+            data = f.read(read_size)
+            if not data:
+                break
+            yield data
+    finally:
+        # Best-effort cleanup; the file may already be closed by external code.
+        try:
+            cur = video_file_handler.get(file_path)
+            if cur is f:
+                video_file_handler.pop(file_path, None)
+            if f is not None:
+                f.close()
+        except Exception:
+            pass
 
 
-def _get_range_header(range_header: str, file_size: int) -> tuple[int, int]:
+def _get_range_header(range_header: str, file_size: int) -> Tuple[int, int]:
     def _invalid_range():
         return HTTPException(
             status.HTTP_416_REQUESTED_RANGE_NOT_SATISFIABLE,
             detail=f"Invalid request range (Range:{range_header!r})",
         )
 
+    # RFC7233 supports:
+    # - bytes=START-END
+    # - bytes=START-
+    # - bytes=-SUFFIX_LENGTH
+    # Browsers usually send a single range; if multiple, we take the first one.
     try:
-        h = range_header.replace("bytes=", "").split("-")
-        start = int(h[0]) if h[0] != "" else 0
-        end = int(h[1]) if h[1] != "" else file_size - 1
-    except ValueError:
+        raw = range_header.strip()
+        if not raw.startswith("bytes="):
+            raise _invalid_range()
+        raw = raw[len("bytes=") :].split(",")[0].strip()
+        start_s, end_s = raw.split("-", 1)
+
+        # suffix-byte-range-spec: bytes=-<length>
+        if start_s == "" and end_s != "":
+            suffix_len = int(end_s)
+            if suffix_len <= 0:
+                raise _invalid_range()
+            start = max(file_size - suffix_len, 0)
+            end = file_size - 1
+        else:
+            start = int(start_s) if start_s != "" else 0
+            end = int(end_s) if end_s != "" else file_size - 1
+    except HTTPException:
+        raise
+    except Exception:
         raise _invalid_range()
 
     if start > end or start < 0 or end > file_size - 1: