Fix Choppy streaming

app.py

@@ -1,9 +1,10 @@
 import os
+import re
 import sys
 from pathlib import Path
 
 from dotenv import load_dotenv
-from flask import Flask, abort, render_template, send_file
+from flask import Flask, Response, abort, render_template, request
 
 load_dotenv()
 
@@ -51,7 +52,48 @@ def play(path):
 @app.route("/video/<path:path>")
 def serve_video(path):
     full = _validate_path(path)
-    return send_file(full, mimetype="video/mp4")
+    file_size = full.stat().st_size
+    range_header = request.headers.get("Range")
+
+    if not range_header:
+        return _stream_file(full, 0, file_size - 1, file_size, 200)
+
+    match = re.match(r"bytes=(\d+)-(\d*)", range_header)
+    if not match:
+        abort(416)
+
+    start = int(match.group(1))
+    end_str = match.group(2)
+    end = int(end_str) if end_str else file_size - 1
+
+    if start >= file_size or end >= file_size or start > end:
+        abort(416)
+
+    content_length = end - start + 1
+    return _stream_file(full, start, end, content_length, 206)
+
+
+def _stream_file(path, start, end, content_length, status):
+    def generate():
+        with open(path, "rb") as f:
+            f.seek(start)
+            remaining = content_length
+            while remaining > 0:
+                chunk_size = min(8192, remaining)
+                data = f.read(chunk_size)
+                if not data:
+                    break
+                remaining -= len(data)
+                yield data
+
+    file_size = path.stat().st_size
+    headers = {
+        "Content-Range": f"bytes {start}-{end}/{file_size}",
+        "Accept-Ranges": "bytes",
+        "Content-Length": str(content_length),
+        "Content-Type": "video/mp4",
+    }
+    return Response(generate(), status=status, headers=headers)
 
 
 if __name__ == "__main__":