Attempt to reduce leak of ffmpeg previews

cista/preview.py

@@ -10,6 +10,7 @@ from wsgiref.handlers import format_date_time
 import av
 import av.datasets
 import fitz  # PyMuPDF
+from av.streams import SideData
 from PIL import Image
 from sanic import Blueprint, empty, raw
 from sanic.exceptions import NotFound
@@ -97,24 +98,20 @@ def process_pdf(path, *, maxsize, maxzoom, quality, page_number=0):
 def process_video(path, *, maxsize, quality):
     with av.open(str(path)) as container:
         stream = container.streams.video[0]
-        rotation = (
-            stream.side_data
-            and stream.side_data.get(av.stream.SideData.DISPLAYMATRIX)
-            or 0
-        )
         stream.codec_context.skip_frame = "NONKEY"
+        stream.codec_context.threads = 1
+        rot = stream.side_data and stream.side_data.get(SideData.DISPLAYMATRIX) or 0
         container.seek(container.duration // 8)
-        frame = next(container.decode(stream))
-        img = frame.to_image()
-        del frame, stream
+        img = next(container.decode(stream)).to_image()
+        del stream
 
     img.thumbnail((maxsize, maxsize))
     imgdata = io.BytesIO()
-        if rotation:
-            img = img.rotate(rotation, expand=True)
+    if rot:
+        img = img.rotate(rot, expand=True)
     img.save(imgdata, format="webp", quality=quality, method=4)
     del img
-
     ret = imgdata.getvalue()
+    del imgdata
     gc.collect()
     return ret