increase atol to 3 for webm

Author: Dan-Flores

src/torchcodec/_core/Encoder.cpp

@@ -648,8 +648,7 @@ void VideoEncoder::initializeEncoder(
         videoStreamOptions.pixelFormat.value());
   } else {
     const AVPixelFormat* formats = getSupportedPixelFormats(*avCodec);
-    // If pixel formats are undefined for some reason, try a broadly supported
-    // default.
+    // If pixel formats are undefined for some reason, try yuv420p
     outPixelFormat_ = (formats && formats[0] != AV_PIX_FMT_NONE)
         ? formats[0]
         : AV_PIX_FMT_YUV420P;

test/test_ops.py

@@ -1205,7 +1205,7 @@ def test_video_encoder_round_trip(self, tmp_path, format, method):
             atol = 15
         else:
             assert_close = torch.testing.assert_close
-            atol = 2
+            atol = 3 if format == "webm" else 2
         for s_frame, rt_frame in zip(source_frames, round_trip_frames):
             assert psnr(s_frame, rt_frame) > 30
             assert_close(s_frame, rt_frame, atol=atol, rtol=0)