AlexxIT/go2rtc · error

y4m: unsupported format

Error message

y4m: unsupported format: %s

What it means

pkg/y4m.Open parses a Y4M (YUV4MPEG2) header and computes the frame size with GetSize. If GetSize returns 0, the header's colorspace/format parameter (e.g. C420jpeg, C422, C444...) is not a format the library can size, meaning the pixel format is unsupported and Open refuses the stream. The error message includes the raw header line for diagnosis.

Solutions

1. Convert the file to a standard 8-bit 4:2:0 Y4M: ffmpeg -i in.y4m -pix_fmt yuv420p -f rawvideo - | with a y4m header, e.g. use -f yuv4mpegpipe -pix_fmt yuv420p
2. Inspect the header line shown in the error to see the offending C parameter
3. Regenerate the source with 8-bit pixel formats (yuv420p/yuv422p/yuv444p) rather than 10/12-bit

Example fix

// before
ffmpeg -i in.mp4 -pix_fmt yuv420p10le -f yuv4mpegpipe out.y4m // unsupported
// after
ffmpeg -i in.mp4 -pix_fmt yuv420p -f yuv4mpegpipe out.y4m

// parse the y4m header before opening
fmtp := y4m.ParseHeader(headerBytes)
if y4m.GetSize(fmtp) == 0 {
    // convert with ffmpeg -pix_fmt yuv420p -f yuv4mpegpipe first
}

if err != nil {
    if strings.Contains(err.Error(), "unsupported format") {
        // fall back to a transcoded copy of the input
    }
    return err
}

When it happens

Trigger: Calling y4m Open on a file whose header contains an unsupported 'C' colorspace parameter (or a header missing the dimension parameters entirely), making frame size computation impossible.

Common situations: Feeding Y4M files with exotic colorspaces (C420p10, C420, alpha planes) generated by ffmpeg with high-bit-depth pixel formats; truncated or corrupted headers; test patterns from tools emitting non-standard Y4M variants.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• ErrCantGetTrack
• kasa: unsupported type:
• nest: invalid cache key format
• v4l2: invalid video_size
• v4l2: invalid input_format

AI-assisted analysis of AlexxIT/go2rtc@c245815e75 (2026-09-07). Data as JSON: /api/errors/b66ecb0ddf8704ea. Report an issue: GitHub.

Appendix: source

Thrown at pkg/y4m/producer.go:24

	"io"

	"github.com/AlexxIT/go2rtc/pkg/core"
	"github.com/pion/rtp"
)

func Open(r io.Reader) (*Producer, error) {
	rd := bufio.NewReaderSize(r, core.BufferSize)
	b, err := rd.ReadBytes('\n')
	if err != nil {
		return nil, err
	}

	b = b[:len(b)-1] // remove \n

	fmtp := ParseHeader(b)

	if GetSize(fmtp) == 0 {
		return nil, errors.New("y4m: unsupported format: " + string(b))
	}

	medias := []*core.Media{
		{
			Kind:      core.KindVideo,
			Direction: core.DirectionRecvonly,
			Codecs: []*core.Codec{
				{
					Name:        core.CodecRAW,
					ClockRate:   90000,
					FmtpLine:    fmtp,
					PayloadType: core.PayloadTypeRAW,
				},
			},
		},
	}
	return &Producer{
		Connection: core.Connection{

View on GitHub (pinned to c245815e75)