Add node video previews

[christian-byrne]

Adds support for nodes with video previews.

load-video-node.mp4

To specify that a node should support video upload (including drag-and-drop, paste, file upload), use video_upload in the input options dict:

class LoadVideo:
    @classmethod
    def INPUT_TYPES(s):
        input_dir = folder_paths.get_input_directory()
        return {"required":
                    {"video": (folder_paths.filter_files_content_types(os.listdir(input_dir), ["video"]), 
                               {"video_upload": True})}, # use `video_upload` flag
                }

To specify that a node should output video previews:

        results = [{
            "filename": "video.webm",
            "subfolder": subfolder,
            "type": "output"
        }]
        return { "ui": { "images": results, "animated": (True,) } }

Note: image inputs (and image nodes) are now identified by checking for a combo input with the image_upload property, rather than checking for a required input named 'image.'

For followup PRs:

• Support parsing WEBM metadata for workflow load
• When pasting video onto empty canvas, create and populate Load WEBM node, as with Load Image. Must wait until the node is added to core.

┆Issue is synchronized with this Notion page by Unito

[huchenlei]

LGTM

[christian-byrne]

Still need to finish output previews migration and implement metadata parse / workflow load.

Edit: metadata parse will be implemented in followup PR.

Using with WEBM nodes:

webm.mp4