ComfyUI/custom_nodes/ComfyUI-VideoHelperSuite/video_formats/webm.json

{
    "main_pass":
    [
        "-n",
        "-pix_fmt", ["pix_fmt",["yuv420p","yuva420p"]],
        "-crf", ["crf","INT", {"default": 20, "min": 0, "max": 100, "step": 1}],
        "-b:v", "0"
    ],
    "audio_pass": ["-c:a", "libvorbis"],
    "save_metadata": ["save_metadata", "BOOLEAN", {"default": true}],
    "extension": "webm"
}