v4l

package module
v0.0.0-...-995f703 Latest Latest
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 Go to latest Published: May 20, 2018 License: GPL-3.0 Imports: 5 Imported by: 0

Documentation

Overview

Package v4l is a facade to the Video4Linux video capture interface.

Index

Constants

View Source 
const (
	// Integer controls
	CtrlBrightness            = 0x00980900
	CtrlContrast              = 0x00980901
	CtrlSaturation            = 0x00980902
	CtrlHue                   = 0x00980903
	CtrlGamma                 = 0x00980910
	CtrlExposure              = 0x00980911
	CtrlGain                  = 0x00980913
	CtrlWhiteBalance          = 0x0098091a
	CtrlSharpness             = 0x0098091b
	CtrlBacklightCompensation = 0x0098091c

	// Boolean controls
	CtrlHFlip            = 0x00980914
	CtrlVFlip            = 0x00980915
	CtrlAutoWhiteBalance = 0x0098090c
	CtrlAutoGain         = 0x00980912
	CtrlAutoHue          = 0x00980919
	CtrlAutoBrightness   = 0x00980920

	// Enums
	CtrlPowerLineFreq     = 0x00980918
	PowerLineFreqDisabled = 0
	PowerLineFreq50Hz     = 1
	PowerLineFreq60Hz     = 2
	PowerLineFreqAuto     = 3

	// Buttons
	CtrlDoWhiteBalance = 0x0098090d
)

Control IDs. Devices may have other controls than these, including custom (driver specific) ones.

View Source 
const (
	// ErrWrongDevice is returned by Open when attempting to open a file that is
	// not a V4L capture device.
	ErrWrongDevice = Error("not a V4L capture device")

	// ErrUnsupported indicates that an operation failed due to a limitation of
	// this library.
	ErrUnsupported = Error("unsupported device or operation")

	// ErrBufferGone is returned by methods of Buffer when the contents of the
	// buffer is no longer available.
	ErrBufferGone = Error("buffer contents not available")
)

Variables

This section is empty.

Functions

This section is empty.

Types

type Buffer 

type Buffer struct {
	// contains filtered or unexported fields
}

A Buffer holds the raw image data of a frame captured from a Device. It implements io.Reader, io.ByteReader, io.ReaderAt, and io.Seeker. A call to Capture, Close, or TurnOff on the corresponding Device may cause the contents of the buffer to go away.

func (*Buffer) Len 

func (b *Buffer) Len() int

Len returns the number of unread bytes in the buffer. If the data is no longer available, it returns 0.

func (*Buffer) Read 

func (b *Buffer) Read(dst []byte) (int, error)

Read reads up to len(dst) bytes into dst, and returns the number of bytes read, along with any error encountered.

func (*Buffer) ReadAt 

func (b *Buffer) ReadAt(dst []byte, offset int64) (int, error)

ReadAt reads up to len(dst) bytes into dst starting at the specified offset, and returns the number of bytes read, along with any error encountered. The seek offset is unaffected by ReadAt.

func (*Buffer) ReadByte 

func (b *Buffer) ReadByte() (byte, error)

ReadByte returns the next byte in the buffer.

func (*Buffer) Seek 

func (b *Buffer) Seek(offset int64, whence int) (int64, error)

Seek sets the seek offset.

func (*Buffer) SeqNum 

func (b *Buffer) SeqNum() uint32

SeqNum returns the sequence number of the frame in the buffer as reported by the kernel.

func (*Buffer) Size 

func (b *Buffer) Size() int64

Size returns the total number of bytes in the buffer. As long as the data is available, the return value is constant and unaffected by calls to the methods of Buffer. If the data is no longer available, it returns 0.

type BufferInfo 

type BufferInfo struct {
	// BufferSize is the number of bytes required to hold an image. For variable
	// length compressed formats, it's the maximum size an image may take up.
	BufferSize int

	// ImageStride is the distance in bytes between the leftmost pixels of
	// adjacent lines.
	ImageStride int
}

A BufferInfo provides information about how image data is laid out in a buffer.

type ControlInfo 

type ControlInfo struct {
	// CID is the identifier of the control. (e.g. 0x00980900)
	CID uint32

	// Name is the name of the control. (e.g. "Brightness")
	Name string

	// Type is the type of the control, one of "int", "bool", "enum",
	// or "button".
	//   - The valid values of an integer control are determined by Min, Max,
	//     and Step.
	//   - A boolean control can only have the values 0 and 1, where 0 means
	//     "disabled" and 1 means "enabled".
	//   - Enums can only take values from a predefined set. (see Options)
	//   - Buttons perform some action when pushed, and they don't have a value.
	//     Reading the value of a button fails, while setting it to any value is
	//     interpreted as a push.
	Type string

	// Min and Max specify the range of values the control can take, and Step is
	// the smallest change actually affecting the hardware. They are only
	// meaningful for integer type controls.
	Min  int32
	Max  int32
	Step int32

	// Default is the default value of the control.
	Default int32

	// Options is the list of valid values of an enum type control. For other
	// types it's nil.
	Options []struct {
		Value int32
		Name  string
	}
}

A ControlInfo provides information about a control.

type Device 

type Device struct {
	// contains filtered or unexported fields
}

A Device represents a V4L capture device.

func Open 

func Open(path string) (*Device, error)

Open opens the capture device named by path. If the file is not a capture device, it fails with ErrWrongDevice.

func (*Device) BufferInfo 

func (d *Device) BufferInfo() (BufferInfo, error)

BufferInfo returns information about how image data is laid out in a buffer. For the same device configuration it always returns the same value.

func (*Device) Capture 

func (d *Device) Capture() (*Buffer, error)

Capture grabs the next frame, and returns a new Buffer holding the raw image data. The device must be turned on for Capture to succeed. A call to Capture may render the contents of previously captured buffers unavailable.

func (*Device) Close 

func (d *Device) Close()

Close closes the device, freeing all native resources associated with it. It stops any capture session in progress, and it may also render the contents of previously captured buffers unavailable.

func (*Device) ControlInfo 

func (d *Device) ControlInfo(cid uint32) (ControlInfo, error)

ControlInfo returns information about a control.

func (*Device) DeviceInfo 

func (d *Device) DeviceInfo() (DeviceInfo, error)

DeviceInfo returns information about the device.

func (*Device) GetConfig 

func (d *Device) GetConfig() (DeviceConfig, error)

GetConfig returns the current configuration of the device.

func (*Device) GetControl 

func (d *Device) GetControl(cid uint32) (int32, error)

GetControl returns the current value of a control.

func (*Device) ListConfigs 

func (d *Device) ListConfigs() ([]DeviceConfig, error)

ListConfigs returns a slice of all valid configurations of the device. It may fail with ErrUnsupported.

func (*Device) ListControls 

func (d *Device) ListControls() ([]ControlInfo, error)

ListControls returns the ControlInfo for every control the device has.

func (*Device) SetConfig 

func (d *Device) SetConfig(cfg DeviceConfig) error

SetConfig configures the device according to cfg. The configuration actually applied may be different from what was requested, as drivers are allowed to adjust the parameters against hardware capabilities (or even completely ignore them). The configuration cannot be changed while the device is turned on.

func (*Device) SetControl 

func (d *Device) SetControl(cid uint32, value int32) error

SetControl sets the value of a control.

func (*Device) TurnOff 

func (d *Device) TurnOff()

TurnOff ends the capture session in progress. It does not close the device, so it can be reused for another session.

func (*Device) TurnOn 

func (d *Device) TurnOn() error

TurnOn initiates a capture session with the device. It may fail with ErrUnsupported. While the device is turned on, its configuration cannot be changed.

type DeviceConfig 

type DeviceConfig struct {
	// Format is the four-character code (FourCC) of the pixel format, with the
	// first character at the lowest byte.
	Format uint32

	// Width and Height specify the image dimensions.
	Width  int
	Height int

	// FPS specifies the frame rate.
	FPS Frac
}

A DeviceConfig encapsulates the configuration of a capture device.

type DeviceInfo 

type DeviceInfo struct {
	// Path is the device path. (e.g. /dev/video0)
	Path string

	// DeviceName is the name of the device. (e.g. "Yoyodyne TV/FM")
	DeviceName string

	// BusInfo is the location of the device in the system.
	// (e.g. "PCI:0000:05:06.0")
	BusInfo string

	// DriverName is the name of the driver. (e.g. "bttv")
	DriverName string

	// DriverVersion contains the three components of the driver's version
	// number. (e.g. [3]int{1, 2, 3} for version 1.2.3)
	DriverVersion [3]int

	// Camera tells if the device is a camera. If false, then this is some other
	// kind of capture device, e.g. an analog TV tuner.
	Camera bool
}

A DeviceInfo provides information about a capture device.

func FindDevices 

func FindDevices() []DeviceInfo

FindDevices returns the DeviceInfo for every capture device found in the system. The paths are always returned in absolute form.

type Error 

type Error string

An Error is simply an error message.

func (Error) Error 

func (e Error) Error() string

Error returns e as a string.

type Frac 

type Frac struct {
	N uint32
	D uint32
}

A Frac represents the fractional number N/D.

func (Frac) Cmp 

func (f Frac) Cmp(g Frac) int

Cmp returns -1, 0, or 1 if f is less then, equal to, or greater than g, respectively.

func (Frac) Reduce 

func (f Frac) Reduce() Frac

Reduce returns f reduced to lowest terms.

Source Files

View all Source files

Directories

Path Synopsis
demos
streamcam
Command streamcam streams MJPEG from a V4L device over HTTP.
 Command streamcam streams MJPEG from a V4L device over HTTP.
viewcam
Command viewcam displays the video captured from a V4L device in a GTK-based GUI.
 Command viewcam displays the video captured from a V4L device in a GTK-based GUI.
fmt
mjpeg
Package mjpeg just defines the FourCC of the MJPEG format.
 Package mjpeg just defines the FourCC of the MJPEG format.
yuyv
Package yuyv provides support for the YUYV format.
 Package yuyv provides support for the YUYV format.

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