Support saving Comfy VIDEO type to buffer (#7939)

* get output format when saving to buffer

* add unit tests for writing to file or stream with correct fmt

* handle `to_format=None`

* fix formatting

comfy_api/input_impl/video_types.py

@@ -12,6 +12,46 @@ import torch
 from comfy_api.input import VideoInput
 from comfy_api.util import VideoContainer, VideoCodec, VideoComponents
 
+
+def container_to_output_format(container_format: str | None) -> str | None:
+    """
+    A container's `format` may be a comma-separated list of formats.
+    E.g., iso container's `format` may be `mov,mp4,m4a,3gp,3g2,mj2`.
+    However, writing to a file/stream with `av.open` requires a single format,
+    or `None` to auto-detect.
+    """
+    if not container_format:
+        return None  # Auto-detect
+
+    if "," not in container_format:
+        return container_format
+
+    formats = container_format.split(",")
+    return formats[0]
+
+
+def get_open_write_kwargs(
+    dest: str | io.BytesIO, container_format: str, to_format: str | None
+) -> dict:
+    """Get kwargs for writing a `VideoFromFile` to a file/stream with `av.open`"""
+    open_kwargs = {
+        "mode": "w",
+        # If isobmff, preserve custom metadata tags (workflow, prompt, extra_pnginfo)
+        "options": {"movflags": "use_metadata_tags"},
+    }
+
+    is_write_to_buffer = isinstance(dest, io.BytesIO)
+    if is_write_to_buffer:
+        # Set output format explicitly, since it cannot be inferred from file extension
+        if to_format == VideoContainer.AUTO:
+            to_format = container_format.lower()
+        elif isinstance(to_format, str):
+            to_format = to_format.lower()
+        open_kwargs["format"] = container_to_output_format(to_format)
+
+    return open_kwargs
+
+
 class VideoFromFile(VideoInput):
     """
     Class representing video input from a file.
@@ -89,7 +129,7 @@ class VideoFromFile(VideoInput):
 
     def save_to(
         self,
-        path: str,
+        path: str | io.BytesIO,
         format: VideoContainer = VideoContainer.AUTO,
         codec: VideoCodec = VideoCodec.AUTO,
         metadata: Optional[dict] = None
@@ -116,7 +156,9 @@ class VideoFromFile(VideoInput):
                 )
 
             streams = container.streams
-            with av.open(path, mode='w', options={"movflags": "use_metadata_tags"}) as output_container:
+
+            open_kwargs = get_open_write_kwargs(path, container_format, format)
+            with av.open(path, **open_kwargs) as output_container:
                 # Copy over the original metadata
                 for key, value in container.metadata.items():
                     if metadata is None or key not in metadata:

tests-unit/comfy_api_test/input_impl_test.py

@@ -0,0 +1,91 @@
+import io
+from comfy_api.input_impl.video_types import (
+    container_to_output_format,
+    get_open_write_kwargs,
+)
+from comfy_api.util import VideoContainer
+
+
+def test_container_to_output_format_empty_string():
+    """Test that an empty string input returns None. `None` arg allows default auto-detection."""
+    assert container_to_output_format("") is None
+
+
+def test_container_to_output_format_none():
+    """Test that None input returns None."""
+    assert container_to_output_format(None) is None
+
+
+def test_container_to_output_format_comma_separated():
+    """Test that a comma-separated list returns a valid singular format from the list."""
+    comma_separated_format = "mp4,mov,m4a"
+    output_format = container_to_output_format(comma_separated_format)
+    assert output_format in comma_separated_format
+
+
+def test_container_to_output_format_single():
+    """Test that a single format string (not comma-separated list) is returned as is."""
+    assert container_to_output_format("mp4") == "mp4"
+
+
+def test_get_open_write_kwargs_filepath_no_format():
+    """Test that 'format' kwarg is NOT set when dest is a file path."""
+    kwargs_auto = get_open_write_kwargs("output.mp4", "mp4", VideoContainer.AUTO)
+    assert "format" not in kwargs_auto, "Format should not be set for file paths (AUTO)"
+
+    kwargs_specific = get_open_write_kwargs("output.avi", "mp4", "avi")
+    fail_msg = "Format should not be set for file paths (Specific)"
+    assert "format" not in kwargs_specific, fail_msg
+
+
+def test_get_open_write_kwargs_base_options_mode():
+    """Test basic kwargs for file path: mode and movflags."""
+    kwargs = get_open_write_kwargs("output.mp4", "mp4", VideoContainer.AUTO)
+    assert kwargs["mode"] == "w", "mode should be set to write"
+
+    fail_msg = "movflags should be set to preserve custom metadata tags"
+    assert "movflags" in kwargs["options"], fail_msg
+    assert kwargs["options"]["movflags"] == "use_metadata_tags", fail_msg
+
+
+def test_get_open_write_kwargs_bytesio_auto_format():
+    """Test kwargs for BytesIO dest with AUTO format."""
+    dest = io.BytesIO()
+    container_fmt = "mov,mp4,m4a"
+    kwargs = get_open_write_kwargs(dest, container_fmt, VideoContainer.AUTO)
+
+    assert kwargs["mode"] == "w"
+    assert kwargs["options"]["movflags"] == "use_metadata_tags"
+
+    fail_msg = (
+        "Format should be a valid format from the container's format list when AUTO"
+    )
+    assert kwargs["format"] in container_fmt, fail_msg
+
+
+def test_get_open_write_kwargs_bytesio_specific_format():
+    """Test kwargs for BytesIO dest with a specific single format."""
+    dest = io.BytesIO()
+    container_fmt = "avi"
+    to_fmt = VideoContainer.MP4
+    kwargs = get_open_write_kwargs(dest, container_fmt, to_fmt)
+
+    assert kwargs["mode"] == "w"
+    assert kwargs["options"]["movflags"] == "use_metadata_tags"
+
+    fail_msg = "Format should be the specified format (lowercased) when output format is not AUTO"
+    assert kwargs["format"] == "mp4", fail_msg
+
+
+def test_get_open_write_kwargs_bytesio_specific_format_list():
+    """Test kwargs for BytesIO dest with a specific comma-separated format."""
+    dest = io.BytesIO()
+    container_fmt = "avi"
+    to_fmt = "mov,mp4,m4a"  # A format string that is a list
+    kwargs = get_open_write_kwargs(dest, container_fmt, to_fmt)
+
+    assert kwargs["mode"] == "w"
+    assert kwargs["options"]["movflags"] == "use_metadata_tags"
+
+    fail_msg = "Format should be a valid format from the specified format list when output format is not AUTO"
+    assert kwargs["format"] in to_fmt, fail_msg