Comfy-Org/ComfyUI · error · ValueError

Only H264 codec is supported for now

Error message

Only H264 codec is supported for now

What it means

The video output helper hard-codes H.264 as the only supported codec for the MP4 writer. Any VideoCodec other than AUTO or H264 (e.g. HEVC, VP9, AV1) hits an explicit guard in mp4_output_open_kwargs and raises, because the writer's stream setup (h264 stream, pix_fmt, crf handling) is specialized for H.264.

Source

Thrown at comfy_api/latest/_input_impl/video_types.py:107

            break
    return 0, 0


def write_output_metadata(container: InputContainer, output, metadata: dict | None):
    """Copy the source container's metadata, then overlay the caller's tags."""
    for key, value in container.metadata.items():
        if metadata is None or key not in metadata:
            output.metadata[key] = value
    if metadata is not None:
        for key, value in metadata.items():
            output.metadata[key] = value if isinstance(value, str) else json.dumps(value)


def mp4_output_open_kwargs(path: str | io.BytesIO, format: VideoContainer, codec: VideoCodec) -> dict:
    if format != VideoContainer.AUTO and format != VideoContainer.MP4:
        raise ValueError("Only MP4 format is supported for now")
    if codec != VideoCodec.AUTO and codec != VideoCodec.H264:
        raise ValueError("Only H264 codec is supported for now")
    # FFmpeg's faststart pass reopens the output by filename, so it cannot be used with file-like objects.
    movflags = "use_metadata_tags+faststart" if isinstance(path, (str, os.PathLike)) else "use_metadata_tags"
    open_kwargs = {"mode": "w", "options": {"movflags": movflags}}
    if isinstance(format, VideoContainer) and format != VideoContainer.AUTO:
        open_kwargs["format"] = format.value
    elif isinstance(path, io.BytesIO):
        open_kwargs["format"] = "mp4"  # no file extension to infer the format from
    return open_kwargs


class VideoFromFile(VideoInput):
    """
    Class representing video input from a file.
    """

    def __init__(self, file: str | io.BytesIO, *, start_time: float=0, duration: float=0):
        """
        Initialize the VideoFromFile object based off of either a path on disk or a BytesIO object

View on GitHub (pinned to 1c6d8d45b3)

Solutions

1. Use codec=VideoCodec.AUTO or VideoCodec.H264
2. Limit the codec input list to auto/h264 until other codecs are implemented
3. Need HEVC/VP9? Export as MP4/H264 here and re-encode externally

Example fix

// before
save_video(..., codec=VideoCodec.HEVC)

// after
save_video(..., codec=VideoCodec.H264)

if codec not in (VideoCodec.AUTO, VideoCodec.H264):
    codec = VideoCodec.H264  # or reject the request before reaching the writer

def is_supported_codec(c) -> bool:
    return c in (VideoCodec.AUTO, VideoCodec.H264)

When it happens

Trigger: Calling video output with codec=VideoCodec.HEVC (or any non-H264 codec) passed through from a node parameter or API call.

Common situations: UI exposes codec options not yet wired in the backend; users migrating from an ffmpeg wrapper that accepted hevc; automation scripts passing codec names as strings that coerce to other enum values.

Related errors

• Only MP4 format is supported for now
• H.264 output requires even dimensions, got {out_width}x{out_
• Could not convert the input video to {container.value.upper(
• {type(model).__name__} must implement map_context_window_to_
• ar_video sampler requires 5-D video latents [B,C,T,H,W], got

AI-assisted analysis of Comfy-Org/ComfyUI@1c6d8d45b3 (2026-08-14). Data as JSON: /api/errors/9098e6b9fefe105d. Report an issue: GitHub.