python-codecs: improve pyav for zero latency

plugins/python-codecs/src/libav.py

@@ -4,6 +4,8 @@ from typing import Any
 import vipsimage
 import pilimage
 from generator_common import createVideoFrame, createImageMediaObject
+import threading
+import asyncio
 
 av = None
 try:
@@ -29,21 +31,33 @@ async def generateVideoFramesLibav(mediaObject: scrypted_sdk.MediaObject, option
 
     gray = options and options.get('format') == 'gray'
 
-    start = 0
+    sampleQueue = asyncio.Queue(1)
+    loop = asyncio.get_event_loop()
+
+    def threadMain():
+        try:
+            for idx, frame in enumerate(container.decode(stream)):
+                try:
+                    # non blocking put may fail if queue is not empty
+                    sampleQueue.put_nowait(frame)
+                except:
+                    pass
+        except:
+            asyncio.run_coroutine_threadsafe(sampleQueue.put(None), loop = loop)
+
+    thread = threading.Thread(target=threadMain)
+    thread.start()
+
     try:
         vipsImage: vipsimage.VipsImage = None
         pilImage: pilimage.PILImage = None
         mo: scrypted_sdk.MediaObject = None
 
-        for idx, frame in enumerate(container.decode(stream)):
-            now = time.time()
-            if not start:
-                start = now
-            elapsed = now - start
-            if (frame.time or 0) < elapsed - 0.500:
-                # print('too slow, skipping frame')
-                continue
-            # print(frame)
+        while True:
+            frame = await sampleQueue.get()
+            if not frame:
+                break
+
             if vipsimage.pyvips:
                 if gray and frame.format.name.startswith('yuv') and frame.planes and len(frame.planes):
                     vips = vipsimage.new_from_memory(memoryview(frame.planes[0]), frame.width, frame.height, 1)