Fix Windows compatibility: pipe streamlink→ffmpeg manually

On Windows, asyncio subprocess stdin can't accept another process's
StreamReader directly. Use a background task to forward data instead.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

capture.py

@@ -1,8 +1,22 @@
 import asyncio
-import struct
 from collections.abc import AsyncIterator
 
 
+async def _pipe_stream(source: asyncio.StreamReader, dest: asyncio.StreamWriter):
+    """Forward data from streamlink stdout to ffmpeg stdin."""
+    try:
+        while True:
+            chunk = await source.read(65536)
+            if not chunk:
+                break
+            dest.write(chunk)
+            await dest.drain()
+    except (BrokenPipeError, ConnectionResetError):
+        pass
+    finally:
+        dest.close()
+
+
 async def capture_frames(
     channel: str, quality: str, interval: int
 ) -> AsyncIterator[bytes]:
@@ -35,13 +49,15 @@ async def capture_frames(
 
     ffmpeg_proc = await asyncio.create_subprocess_exec(
         *ffmpeg_cmd,
-        stdin=streamlink_proc.stdout,
+        stdin=asyncio.subprocess.PIPE,
         stdout=asyncio.subprocess.PIPE,
         stderr=asyncio.subprocess.DEVNULL,
     )
 
-    # Release streamlink's stdout so ffmpeg owns the pipe
+    # Forward streamlink → ffmpeg in background
-    streamlink_proc.stdout = None
+    pipe_task = asyncio.create_task(
+        _pipe_stream(streamlink_proc.stdout, ffmpeg_proc.stdin)
+    )
 
     try:
         buf = b""
@@ -59,13 +75,13 @@ async def capture_frames(
                     break
                 eoi = buf.find(b"\xff\xd9", soi + 2)
                 if eoi == -1:
-                    # Keep from SOI onward, discard junk before
                     buf = buf[soi:]
                     break
                 frame = buf[soi : eoi + 2]
                 buf = buf[eoi + 2 :]
                 yield frame
     finally:
+        pipe_task.cancel()
         for proc in (ffmpeg_proc, streamlink_proc):
             try:
                 proc.terminate()