Make crf optional

Author: Daniel Flores

src/torchcodec/_core/custom_ops.cpp

@@ -33,7 +33,7 @@ TORCH_LIBRARY(torchcodec_ns, m) {
   m.def(
       "encode_audio_to_file(Tensor samples, int sample_rate, str filename, int? bit_rate=None, int? num_channels=None, int? desired_sample_rate=None) -> ()");
   m.def(
-      "encode_video_to_file(Tensor frames, int frame_rate, str filename, int crf) -> ()");
+      "encode_video_to_file(Tensor frames, int frame_rate, str filename, int? crf=None) -> ()");
   m.def(
       "encode_audio_to_tensor(Tensor samples, int sample_rate, str format, int? bit_rate=None, int? num_channels=None, int? desired_sample_rate=None) -> Tensor");
   m.def(
@@ -435,7 +435,7 @@ void encode_video_to_file(
     const at::Tensor& frames,
     int64_t frame_rate,
     std::string_view file_name,
-    int64_t crf) {
+    std::optional<int64_t> crf = std::nullopt) {
   VideoStreamOptions videoStreamOptions;
   videoStreamOptions.crf = crf;
   VideoEncoder(

src/torchcodec/_core/ops.py

@@ -230,7 +230,7 @@ def encode_video_to_file_abstract(
     frames: torch.Tensor,
     frame_rate: int,
     filename: str,
-    crf: int,
+    crf: Optional[int],
 ) -> None:
     return
 

test/test_ops.py

@@ -1285,11 +1285,12 @@ def test_video_encoder_test_round_trip(self, tmp_path, format):
 
         encoded_path = str(tmp_path / f"encoder_output.{format}")
         frame_rate = 30  # Frame rate is fixed with num frames decoded
-        encode_video_to_file(source_frames, frame_rate, encoded_path, 0)
+        encode_video_to_file(source_frames, frame_rate, encoded_path, crf=0)
         round_trip_frames = self.decode(encoded_path).data
 
-        # The output pixel format depends on the codecs available, and FFmpeg version.
-        # In the cases where YUV420P is chosen and chroma subsampling happens, assert_close needs higher tolerance.
+        # In the cases where a lossy pixel format conversion occurs, higher tolerance is needed.
+        # Converting to the output format may perform chroma subsampling.
+        # Other times, no conversion between YUV and RGB is required.
         if ffmpeg_version == 6 or format in ("avi", "flv"):
             atol = 55
         else: