Show camera name and pixel format in startup banner

camera/camera.go

@@ -22,6 +22,45 @@ type DeviceInfo struct {
 	Name  string
 }
 
+// Info describes the negotiated capture format.
+type Info struct {
+	Format string
+	Width  int
+	Height int
+}
+
+// fourccName returns a readable name for a V4L/VfW pixel format.
+func fourccName(format uint32) string {
+	switch format {
+	case mjpgFourCC:
+		return "MJPEG"
+	case jpegFourCC:
+		return "JPEG"
+	case yuyvFourCC, yuy2FourCC:
+		return "YUYV"
+	case uyvyFourCC:
+		return "UYVY"
+	case yvyuFourCC:
+		return "YVYU"
+	case vyuyFourCC:
+		return "VYUY"
+	case nv12FourCC:
+		return "NV12"
+	case yu12FourCC:
+		return "YU12"
+	case yv12FourCC:
+		return "YV12"
+	case rgb24FourCC:
+		return "RGB24"
+	case bgr24FourCC:
+		return "BGR24"
+	case greyFourCC:
+		return "GREY"
+	}
+
+	return string([]byte{byte(format), byte(format >> 8), byte(format >> 16), byte(format >> 24)})
+}
+
 var (
 	yuy2FourCC  = fourcc("YUY2")
 	yuyvFourCC  = fourcc("YUYV")

camera/camera_darwin.go

@@ -100,6 +100,11 @@ func New(opts Options) (c *Camera, err error) {
 	return c, nil
 }
 
+// Info returns the negotiated capture format.
+func (c *Camera) Info() Info {
+	return Info{Format: "BGRA", Width: int(c.opts.Width), Height: int(c.opts.Height)}
+}
+
 // Devices returns the available capture devices.
 func Devices() ([]DeviceInfo, error) {
 	if err := loadFrameworks(); err != nil {

camera/camera_linux.go

@@ -215,6 +215,11 @@ func (c *Camera) Close() (err error) {
 	return
 }
 
+// Info returns the negotiated capture format.
+func (c *Camera) Info() Info {
+	return Info{Format: fourccName(c.config.Format), Width: c.config.Width, Height: c.config.Height}
+}
+
 // Devices returns the available capture devices.
 func Devices() ([]DeviceInfo, error) {
 	infos := v4l.FindDevices()

camera/camera_test.go

@@ -10,6 +10,10 @@ import (
 )
 
 func TestCamera(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping camera test in short mode")
+	}
+
 	camera, err := New(Options{0, 0, "", 640, 480, false, ""})
 	if err != nil {
 		t.Skipf("no camera available: %v", err)

camera/camera_windows_msmf.go

@@ -449,6 +449,11 @@ func nv12ToYCbCr420(data []byte, stride, width, height int, dst *image.YCbCr) {
 	}
 }
 
+// Info returns the negotiated capture format.
+func (c *Camera) Info() Info {
+	return Info{Format: "NV12", Width: c.width, Height: c.height}
+}
+
 // Devices returns the available capture devices.
 func Devices() ([]DeviceInfo, error) {
 	runtime.LockOSThread()

camera/camera_windows_vfw.go

@@ -25,6 +25,8 @@ type Camera struct {
 	className string
 	format    uint32
 	bpp       int
+	width     int
+	height    int
 }
 
 // New returns new Camera for given camera index.
@@ -145,6 +147,9 @@ func (c *Camera) run(ready chan<- error) {
 		height = -height
 	}
 
+	c.width = width
+	c.height = height
+
 	rect := image.Rect(0, 0, width, height)
 
 	switch {
@@ -483,6 +488,16 @@ func capCreateCaptureWindow(lpszWindowName string, dwStyle, x, y, width, height
 	return syscall.Handle(ret), nil
 }
 
+// Info returns the negotiated capture format.
+func (c *Camera) Info() Info {
+	format := fourccName(c.format)
+	if c.format == 0 {
+		format = fmt.Sprintf("RGB%d", c.bpp*8)
+	}
+
+	return Info{Format: format, Width: c.width, Height: c.height}
+}
+
 // Devices returns the available capture devices.
 func Devices() ([]DeviceInfo, error) {
 	var devices []DeviceInfo

cmd/cam2ip/main.go

@@ -139,7 +139,13 @@ func main() {
 
 	defer srv.Reader.Close()
 
-	stderr("%s %s listening on %s\n", name, version, srv.Bind)
+	info := cam.Info()
+	desc := fmt.Sprintf("%dx%d %s", info.Width, info.Height, info.Format)
+	if dn := deviceName(srv.Index); dn != "" {
+		desc = dn + ", " + desc
+	}
+
+	stderr("%s %s [%s] listening on %s\n", name, version, desc, srv.Bind)
 
 	err = srv.ListenAndServe()
 	if err != nil {
@@ -152,6 +158,22 @@ func stderr(format string, a ...any) {
 	_, _ = fmt.Fprintf(os.Stderr, format, a...)
 }
 
+// deviceName returns the name of the camera at the given index, or "" if unknown.
+func deviceName(index int) string {
+	devices, err := camera.Devices()
+	if err != nil {
+		return ""
+	}
+
+	for _, d := range devices {
+		if d.Index == index {
+			return d.Name
+		}
+	}
+
+	return ""
+}
+
 // deviceIndex returns the index of the first camera whose name contains the query.
 func deviceIndex(name string) (int, error) {
 	devices, err := camera.Devices()