vsource_v4l2_web_logo

VSourceV4L2 C++ library

v2.1.6

Overview
Versions
Library files
VSourceV4L2 class description
Data structures
- VSourceCommand enum
- VSourceParam enum
VSourceParams class description
Build and connect to your project
Simple example
Test application

Overview

VSourceV4L2 C++ library provides video capture and video source (V4L2 compatible video sources) control function based on V4L2 API. The library supports stepwise and discrete devices. The library inherits interface from open source VSource interface class. VSource.h file contains data structures VSourceParams class (contains video source params and provides methods for serialization / deserialization params), VSourceCommand enum (describes video source action commands), VSourceParam enum (describes video source params) and includes VSourceV4L2 class declaration. VSourceV4L2 depends on: Libcamera API, VSource interface class (provides interface for video sources, source code included, Apache 2.0 license) and open source Logger library (provides method to write logs, source code included, Apache 2.0 license). The library provides auto detection of supported resolution, format and fps. If particular devices doesn’t support requested pixel format, resolution or fps, the library will set most appropriate parameters. The library supports C++17 standard.

Versions

Table 1 - Library versions.

Version	Release date	What’s new
1.0.0	13.01.2022	First version
1.1.0	20.06.2023	- Fixed bugs. - Documentation updated.
1.2.0	29.06.2023	- Added new parameters. - Documentation updated.
2.0.0	20.08.2023	- Added license. - Added example and updated test application. - Interface update according to VSource class. - Added automatic detection supported format and automatic choosing right format during initialization.
2.0.1	29.08.2023	- Fixed stepwise camera support issue. - Documentation updated.
2.0.2	30.08.2023	- Fixed stepwise camera pixel format setting.
2.0.3	17.11.2023	- Frame class updated.
2.0.4	17.11.2023	- Fixed initialization with string.
2.1.0	22.12.2023	- Region of interest support added.
2.1.1	27.12.2023	- Mistakes in ROI fixed.
2.1.2	09.01.2024	- Documentation updated.
2.1.3	24.04.2024	- Documentation updated. - Submodules updated.
2.1.4	20.05.2024	- Documentation updated. - Submodules updated.
2.1.5	16.07.2024	- CMake updated. - Submodules updated.
2.1.6	13.11.2024	- Fix device initialization in test application.

Library files

The repository structure is shown below:

CMakeLists.txt --------------- Main CMake file of the library.
3rdparty --------------------- Folder with third-party libraries.
    CMakeLists.txt ----------- CMake file to include third-party libraries.
    Logger ------------------- Folder with Logger library source code.
    VSource ------------------ Folder with VSource library source code.
src -------------------------- Folder with library source code.
    CMakeLists.txt ----------- CMake file og the library.
    VSourceV4L2.h ------------ Main library header file.
    VSourceV4L2Version.h ----- Header file with library version.
    VSourceV4L2Version.h.in -- File for CMake to generate version header.
    VSourceV4L2.cpp ---------- C++ implementation file.
test ------------------------- Folder for test application files.
    CMakeLists.txt ----------- CMake file for test application.
    main.cpp ----------------- Source C++ file of demo application.
example ---------------------- Folder for example application files.
    CMakeLists.txt ----------- CMake file for example application.
    main.cpp ----------------- Source C++ file of example application.

Additionally test application depends on OpenCV library to provide user interface.

VSourceV4L2 class description

VSourceV4L2 class declaration

VSourceV4l2 class declared in VSourceV4L2.h file. Class declaration:

namespace cr
{
namespace video
{
/**
 * @brief Video source class based on V4L2 API.
*/
class VSourceV4L2 : public VSource
{
public:

    /// Class constructor.
    VSourceV4L2();

    /// Class destructor.
    ~VSourceV4L2();

    /// Get string of current library version.
    static std::string getVersion();

    /// Open video source.
    bool openVSource(std::string& initString) override;

    /// Init video source.
    bool initVSource(VSourceParams& params) override;

    /// Get open status.
    bool isVSourceOpen() override;

    /// Close video source.
    void closeVSource() override;

    /// Get new video frame.
    bool getFrame(Frame& frame, int32_t timeoutMsec = 0) override;

    /// Set video source param.
    bool setParam(VSourceParam id, float value) override;

    /// Get video source param value.
    float getParam(VSourceParam id) override;

    /// Get video source params structure.
    void getParams(VSourceParams& params) override;

    /// Execute command.
    bool executeCommand(VSourceCommand id) override;

    /// Decode and execute command.
    bool decodeAndExecuteCommand(uint8_t* data, int size) override;
};
}
}

getVersion method

The getVersion() method returns string of current version of VSourceV4L2 class. Method declaration:

static std::string getVersion();

Method can be used without VSourceV4L2 class instance:

std::cout << "VSourceV4L2 v: " << VSourceV4L2::getVersion() << std::endl;

Console output:

VSourceV4L2 v: 2.1.5

openVSource method

The openVSource(…) method initializes video source. Video source parameters (VSourceParams class) will be initialized by default. Instead of openVSource(…) method user can call initVSource(…) method. Method declaration:

bool openVSource(std::string& initString) override;

Parameter	Value
initString	Initialization string. Valid formats: [full device name];[width];[height];[fps];[fourcc] or [full device name];[width];[height];[fps] or [full device name];[width];[height] or [full device name] Initialization string parameters: [full device name] - Full name of video device in Linux OS. Default name format: /dev/video0, /dev/video1 etc. or can be /dev/v4l/by-id/… in case UVC compatible cameras. [width] - Video frame width. Video frame height must be set as well. The library will try set this value in video capture hardware parameters. If set to 0 the library will detect frame width automatically according to existing video device parameters. [height] - Video frame height. Video frame width must be set as well. The library will try set this value in video capture hardware parameters. If set to 0 the library will detect frame width automatically according to existing video device parameters. [fps] - FPS. The library will try set this value in video capture hardware parameters. If set to 0 the library will detect frame width automatically according to existing video device parameters. [fourcc] - Pixel format. Valid values: BGR24, RGB24, GRAY, YUV24, YUYV, UYVY, NV12, NV21, YV12, YU12. If fourcc not set the library will chose appropriate format according to existing video device parameters.

Parameter

Value

initString

Initialization string. Valid formats:
[full device name];[width];[height];[fps];[fourcc] or
[full device name];[width];[height];[fps] or
[full device name];[width];[height] or
[full device name]
Initialization string parameters:
[full device name] - Full name of video device in Linux OS. Default name format: /dev/video0, /dev/video1 etc. or can be /dev/v4l/by-id/… in case UVC compatible cameras.
[width] - Video frame width. Video frame height must be set as well. The library will try set this value in video capture hardware parameters. If set to 0 the library will detect frame width automatically according to existing video device parameters.
[height] - Video frame height. Video frame width must be set as well. The library will try set this value in video capture hardware parameters. If set to 0 the library will detect frame width automatically according to existing video device parameters.
[fps] - FPS. The library will try set this value in video capture hardware parameters. If set to 0 the library will detect frame width automatically according to existing video device parameters.
[fourcc] - Pixel format. Valid values: BGR24, RGB24, GRAY, YUV24, YUYV, UYVY, NV12, NV21, YV12, YU12. If fourcc not set the library will chose appropriate format according to existing video device parameters.

Returns: TRUE if the video source open or FALSE if not.

initVSource method

The initVSource(…) method designed to initialize video source by set of parameters. Instead of initVSource(…) method user can call openVSource(…). Method declaration:

bool initVSource(VSourceParams& params) override;

Parameter	Value
params	VSourceParams class object. The video source will set parameters according to params structure. If particular parameters not valid the library will set it to default.

Returns: TRUE if the video source initialized or FALSE if not.

isVSourceOpen method

The isVSourceOpen() method returns video source initialization status. Initialization status also included in VSourceParams class. Method declaration:

bool isVSourceOpen() override;

Returns: TRUE if the video source open (initialized) or FALSE if not.

closeVSource method

The closeVSource() method intended to close video source. Method declaration:

void closeVSource() override;

getFrame method

The getFrame(…) method returns video frame. Video source supports auto re-initialization in case connection loss. Method declaration:

bool getFrame(Frame& frame, int32_t timeoutMsec = 0) override;

Parameter	Value
frame	Output video frame (see Frame class description). Video source class determines output pixel format. Pixel format can be set in initVSource(…) or openVSource(…) methods but if specified pixel format not supported by hardware the library can return Frame object with different pixel format. The library supports only RAW pixels formats: BGR24, RGB24, GRAY, YUV24, YUYV, UYVY, NV12, NV21, YV12 and YU12.
timeoutMsec	Timeout to wait new frame data, milliseconds: - timeoutMs == -1 - Method will wait endlessly until new data arrive. - timeoutMs == 0 - Method will only check if new data exist. - timeoutMs > 0 - Method will wait new data specified time.

Parameter

Value

frame

Output video frame (see Frame class description). Video source class determines output pixel format. Pixel format can be set in initVSource(…) or openVSource(…) methods but if specified pixel format not supported by hardware the library can return Frame object with different pixel format. The library supports only RAW pixels formats: BGR24, RGB24, GRAY, YUV24, YUYV, UYVY, NV12, NV21, YV12 and YU12.

timeoutMsec

Timeout to wait new frame data, milliseconds:
- timeoutMs == -1 - Method will wait endlessly until new data arrive.
- timeoutMs == 0 - Method will only check if new data exist.
- timeoutMs > 0 - Method will wait new data specified time.

Returns: TRUE if new frame exists and copied or FALSE if not (wait timeout expired or video source not initialized).

setParam method

The setParam(…) method designed to set new video source parameters value. Method will set parameters to device. Method can be used only after video source initialization. Method declaration:

bool setParam(VSourceParam id, float value) override;

Parameter	Description
id	Video source parameter ID according to VSourceParam enum.
value	Video source parameter value.

Returns: TRUE if the parameter was set or FALSE if not (not valid value or not supported).

getParam method

The getParam(…) method designed to obtain video source parameter value. Method will request parameters from device. Method can be used only after video source initialization. Method declaration:

float getParam(VSourceParam id) override;

Parameter	Description
id	Video source parameter ID according to VSourceParam enum.

Returns: parameter value or -1 of the parameter not supported.

getParams method

The getParams(…) method designed to obtain video source params class. Method declaration:

void getParams(VSourceParams& params) override;

Parameter	Description
params	VSourceParams class object.

executeCommand method

The executeCommand(…) method executes video source command. The library doesn’t support commands. Method declaration:

bool executeCommand(VSourceCommand id) override;

Parameter	Description
id	Video source action command ID according to VSourceCommand enum.

Returns: always returns FALSE.

decodeAndExecuteCommand method

The decodeAndExecuteCommand(…) method decodes and executes command on video source side. Method will decode commands which encoded by encodeCommand(…) and encodeSetParamCommand(…) methods of VSource interface class. If command decoded the method will call setParam(…) or executeCommand(…) methods. decodeAndExecuteCommand(…) is thread-safe. This means that the method can be safely called from any thread. Method declaration:

bool decodeAndExecuteCommand(uint8_t* data, int size) override;

Parameter	Description
data	Pointer to input command.
size	Size of command. Must be 11 bytes for SET_PARAM and 7 bytes for COMMAND.

Returns: TRUE if command decoded (SET_PARAM or COMMAND) and executed or FALSE if not.

encodeSetParamCommand method of VSource interface class

The encodeSetParamCommand(…) static method designed to encode command to change any parameter in remote video source. To control video source remotely, the developer has to design his own protocol and according to it encode the command and deliver it over the communication channel. To simplify this, the VSource class contains static methods for encoding the control command. The VSource class provides two types of commands: a parameter change command (SET_PARAM) and an action command (COMMAND). encodeSetParamCommand(…) designed to encode SET_PARAM command. Method declaration:

static void encodeSetParamCommand(uint8_t* data, int& size, VSourceParam id, float value);

Parameter	Description
data	Pointer to data buffer for encoded command. Must have size >= 11.
size	Size of encoded data. Will be 11 bytes.
id	Parameter ID according to VSourceParam enum.
value	Parameter value.

encodeSetParamCommand(…) is static and used without VSource class instance. This method used on client side (control system). Command encoding example:

// Buffer for encoded data.
uint8_t data[11];
// Size of encoded data.
int size = 0;
// Random parameter value.
float outValue = (float)(rand() % 20);
// Encode command.
VSurce::encodeSetParamCommand(data, size, VSourceParam::EXPOSURE, outValue);

encodeCommand method of VSource interface class

The encodeCommand(…) static method designed to encode command to perform action command in remote video source. To control a video source remotely, the developer has to design his own protocol and according to it encode the command and deliver it over the communication channel. To simplify this, the VSource class contains static methods for encoding the control command. The VSource class provides two types of commands: a parameter change command (SET_PARAM) and an action command (COMMAND). encodeCommand(…) designed to encode COMMAND (action command). Method declaration:

static void encodeCommand(uint8_t* data, int& size, VSourceCommand id);

Parameter	Description
data	Pointer to data buffer for encoded command. Must have size >= 7 bytes.
size	Size of encoded data. Will be 7 bytes.
id	Command ID according to VSourceCommand enum.

encodeCommand(…) is static and used without VSource class instance. This method used on client side (control system). Command encoding example:

// Buffer for encoded data.
uint8_t data[11];
// Size of encoded data.
int size = 0;
// Encode command.
VSource::encodeCommand(data, size, VSourceCommand::RESTART);

decodeCommand method of VSource interface class

The decodeCommand(…) static method designed to decode command on video source side (edge device). Method declaration:

static int decodeCommand(uint8_t* data, int size, VSourceParam& paramId, VSourceCommand& commandId, float& value);

Parameter	Description
data	Pointer to input command.
size	Size of command. Should be 11 bytes for SET_PARAM and 7 bytes for COMMAND.
paramId	Parameter ID according to VSourceParam enum. After decoding SET_PARAM command the method will return parameter ID.
commandId	Command ID according to VSourceCommand enum. After decoding COMMAND the method will return command ID.
value	Parameter value (after decoding SET_PARAM command).

Returns: 0 - in case decoding COMMAND, 1 - in case decoding SET_PARAM command or -1 in case errors.

Data structures

VSource.h file of VSource interface class defines IDs for parameters (VSourceParam enum) and IDs for action commands (VSourceCommand enum).

VSourceCommand enum

Enum declaration:

enum class VSourceCommand
{
    /// Restart.
    RESTART = 1
};

Table 2 - Video source commands description.

Command	Description
RESTART	Not supported by VSourceV4L2 library.

VSourceParam enum

Enum declaration:

enum class VSourceParam
{
    /// [read/write] Logging mode. Values: 0 - Disable, 1 - Only file,
    /// 2 - Only terminal, 3 - File and terminal.
    LOG_LEVEL = 1,
    /// [read/write] Frame width. User can set frame width before initialization
    /// or after. Some video source classes may set width automatically.
    WIDTH,
    /// [read/write] Frame height. User can set frame height before
    /// initialization or after. Some video source classes may set height
    /// automatically.
    HEIGHT,
    /// [read/write] Gain mode. Value depends on implementation but it is
    /// recommended to keep default values: 0 - Manual control, 1 - Auto.
    GAIN_MODE,
    /// [read/write] Gain value. Value: 0(min for particular video source class)
    /// - 65535(max for particular video source class).
    GAIN,
    /// [read/write] Exposure mode. Value depends on implementation but it is
    /// recommended to keep default values: 0 - Manual control, 1 - Auto.
    EXPOSURE_MODE,
    /// [read/write] Exposure value. Value: 0(min for particular video source
    /// class) - 65535(max for particular video source class).
    EXPOSURE,
    /// [read/write] Focus mode. Value depends on implementation but it is
    /// recommended to keep default values: 0 - Manual control, 1 - Auto.
    FOCUS_MODE,
    /// [read/write] Focus position. Value: 0(full near) - 65535(full far).
    FOCUS_POS,
    /// [read only] Video capture cycle time. **VSource** class sets this value
    /// automatically. This parameter means time interval between two captured
    /// video frame.
    CYCLE_TIME_MKS,
    /// [read/write] FPS. User can set frame FPS before initialization or after.
    /// Some video source classes may set FPS automatically.
    FPS,
    /// [read only] Open flag. 0 - not open, 1 - open.
    IS_OPEN,
    /// Region of interest upper left corner x coordinate.
    ROI_X,
    /// Region of interest upper left corner y coordinate.
    ROI_Y,
    /// Region of interest width.
    ROI_WIDTH,
    /// Region of interest height.
    ROI_HEIGHT,
    /// [read/write] Custom parameter. Depends on implementation.
    CUSTOM_1,
    /// [read/write] Custom parameter. Depends on implementation.
    CUSTOM_2,
    /// [read/write] Custom parameter. Depends on implementation.
    CUSTOM_3
};

Table 3 - Video source params description. Some params are not supported in VSourceМ4Д2 implementation.

Parameter	Access	Description
LOG_LEVEL	read / write	Logging mode. Specifies the log output mode. Values: 0 - Disable, 1 - Only file, 2 - Only terminal (console), 3 - File and terminal.
WIDTH	read only	Frame width. Can’t be changes after initialization.
HEIGHT	read only	Frame height. Can’t be changes after initialization.
GAIN_MODE	read / write	Gain mode. Values: 0 - Manual control, 1 - Auto. Some V4l2 video source may not support this parameter to control.
GAIN	read / write	Gain value. Value: 0(min) - 65535(max). Some V4l2 video source may not support this parameter to control.
EXPOSURE_MODE	read / write	Exposure mode. Values: 0 - Manual mode, 1 - Auto mode, 2 - Shutter priority, 3 - Aperture priority. Some V4l2 video source may not support this parameter to control.
EXPOSURE	read / write	Exposure value. Value: 0(min) - 65535(max). Some V4l2 video source may not support this parameter to control.
FOCUS_MODE	read / write	Focus mode. Values: 0 - Manual control, 1 - Auto. Some V4l2 video source may not support this parameter to control.
FOCUS_POS	read / write	Focus position. Value: 0(full near) - 65535(full far). Some V4l2 video source may not support this parameter to control.
CYCLE_TIME_MKS	read only	Video capture cycle time, microseconds. The library class sets this value automatically. This parameter means time interval between two captured video frame.
FPS	read / write	FPS. Can’t be changes after initialization.
IS_OPEN	read only	Open flag. 0 - not open, 1 - open.
ROI_X	read / write	Region of interest top-left corner horizontal coordinate. If ROI set the output frame will have size equal to ROI size.
ROI_Y	read / write	Region of interest top-left corner horizontal coordinate. If ROI set the output frame will have size equal to ROI size.
ROI_WIDTH	read / write	Region of interest width, pixels. If ROI set the output frame will have size equal to ROI size.
ROI_HEIGHT	read / write	Region of interest height, pixels. If ROI set the output frame will have size equal to ROI size.
CUSTOM_1	read / write	Not supported. Can have any value.
CUSTOM_2	read / write	Not supported. Can have any value.
CUSTOM_3	read / write	Not supported. Can have any value.

VSourceParams class description

VSourceParams class declaration

VSourceParams class used for video source initialization (initVSource(…) method) or to get all actual params (getParams(…) method). Also VSourceParams provide structure to write/read params from JSON files (JSON_READABLE macro, see ConfigReader class description) and provide methos to encode and decode params. Class declaration:

class VSourceParams
{
public:
    /// Logging mode. Values: 0 - Disable, 1 - Only file,
    /// 2 - Only terminal, 3 - File and terminal.
    int logLevel{0};
    /// Video source: file, video stream, video device, camera num, etc.
    std::string source{"/dev/video0"};
    /// FOURCC: RGB24, BGR24, YUYV, UYVY, GRAY, YUV24, NV12, NV21, YU12, YV12.
    /// Value says to video source class which pixel format preferable for
    /// output video frame. Particular video source class can ignore this params
    /// during initialization. Parameters should be set before initialization.
    std::string fourcc{"YUYV"};
    /// Frame width. User can set frame width before initialization
    /// or after. Some video source classes may set width automatically.
    int width{1920};
    /// Frame height. User can set frame height before
    /// initialization or after. Some video source classes may set height
    /// automatically.
    int height{1080};
    /// Gain mode. Value depends on implementation but it is
    /// recommended to keep default values: 0 - Manual control, 1 - Auto.
    int gainMode{1};
    /// Gain value. Value: 0(min for particular video source class)
    /// - 65535(max for particular video source class).
    int gain{0};
    /// Exposure mode. Value depends on implementation but it is
    /// recommended to keep default values: 0 - Manual control, 1 - Auto.
    int exposureMode{1};
    /// Exposure value. Value: 0(min for particular video source
    /// class) - 65535(max for particular video source class).
    int exposure{1};
    /// Focus mode. Focus mode. Value depends on implementation but it is
    /// recommended to keep default values: 0 - Manual control, 1 - Auto.
    int focusMode{1};
    /// Focus position. Value: 0(full near) - 65535(full far).
    int focusPos{0};
    /// Video capture cycle time. **VSource** class sets this value
    /// automatically. This parameter means time interval between two captured
    /// video frame.
    int cycleTimeMks{0};
    /// FPS. User can set frame FPS before initialization or after.
    /// Some video source classes may set FPS automatically.
    float fps{0};
    /// Open flag. 0 - not open, 1 - open.
    bool isOpen{false};
    /// Region of interest upper left corner x coordinate.
    int roiX{0};
    /// Region of interest upper left corner y coordinate.
    int roiY{0};
    /// Region of interest width.
    int roiWidth{0};
    /// Region of interest height.
    int roiHeight{0};
    /// Custom parameter. Depends on implementation.
    float custom1{0.0f};
    /// Custom parameter. Depends on implementation.
    float custom2{0.0f};
    /// Custom parameter. Depends on implementation.
    float custom3{0.0f};

    JSON_READABLE(VSourceParams, logLevel, source, fourcc, width, height,
                  gainMode, exposureMode, focusMode, fps, roiX, roiY,
                  roiWidth, roiHeight, custom1, custom2, custom3);

    /// Copy operator.
    VSourceParams& operator= (const VSourceParams& src);

    /// Encode (serialize) params.
    bool encode(uint8_t* data, int bufferSize, int& size,
                VSourceParamsMask* mask = nullptr);

    /// Decode (deserialize) params.
    bool decode(uint8_t* data, int dataSize);
};

Table 4 - VSourceParams class fields description.

Field	type	Description
logLevel	int	Logging mode. Specifies the log output mode. Values: 0 - Disable, 1 - Only file, 2 - Only terminal (console), 3 - File and terminal.
source	string	Full name of video device in Linux OS. Default name format: /dev/video0, /dev/video1 etc. or can be /dev/v4l/by-id/… in case UVC compatible cameras.
fourcc	string	Pixel format. Valid values: BGR24, RGB24, GRAY, YUV24, YUYV, UYVY, NV12, NV21, YV12, YU12. If fourcc not set the library will chose appropriate format according to existing video device parameters. Value says to video source class which pixel format preferable for output video frame.
width	int	Video frame width. Video frame height must be set as well. The library will try set this value in video capture hardware parameters. If set to 0 the library will detect frame width automatically according to existing video device parameters.
height	int	Video frame height. Video frame width must be set as well. The library will try set this value in video capture hardware parameters. If set to 0 the library will detect frame width automatically according to existing video device parameters.
gainMode	int	Gain mode. Values: 0 - Manual control, 1 - Auto. Some V4l2 video source may not support this parameter to control.
gain	int	Gain value. Value: 0(min) - 65535(max). Some V4l2 video source may not support this parameter to control.
exposureMode	int	Exposure mode. Values: 0 - Manual mode, 1 - Auto mode, 2 - Shutter priority, 3 - Aperture priority. Some V4l2 video source may not support this parameter to control.
exposure	int	Exposure value. Value: 0(min) - 65535(max). Some V4l2 video source may not support this parameter to control.
focusMode	int	Focus mode. Values: 0 - Manual control, 1 - Auto. Some V4l2 video source may not support this parameter to control.
focusPos	int	Focus position. Value: 0(full near) - 65535(full far). Some V4l2 video source may not support this parameter to control.
cycleTimeMks	int	Video capture cycle time. The library class sets this value automatically. This parameter means time interval between two captured video frame.
fps	float	FPS. User can set frame FPS only before initialization.
isOpen	bool	Open flag. false - not open, true - open.
roiX	int	Region of interest top-left corner horizontal coordinate. If ROI set the output frame will have size equal to ROI size.
roiY	int	Region of interest top-left corner horizontal coordinate. If ROI set the output frame will have size equal to ROI size.
roiWidth	int	Region of interest width, pixels. If ROI set the output frame will have size equal to ROI size.
roiHeight	int	Region of interest height, pixels. If ROI set the output frame will have size equal to ROI size.
custom1	float	Not supported. Can have any value.
custom2	float	Not supported. Can have any value.
custom3	float	Not supported. Can have any value.

None: VSourceParams class fields listed in Table 4 reflects params set/get by methods setParam(…) and getParam(…).

Serialize video source params

VSourceParams class provides method encode(…) to serialize video source params (fields of VSourceParams class, see Table 4). Serialization of video source params necessary in case when you need to send video source params via communication channels. Method doesn’t encode fields: initString and fourcc. Method provides options to exclude particular parameters from serialization. To do this method inserts binary mask (2 bytes) where each bit represents particular parameter and decode(…) method recognizes it. Method declaration:

bool encode(uint8_t* data, int bufferSize, int& size, VSourceParamsMask* mask = nullptr);

Parameter	Value
data	Pointer to data buffer.
size	Size of encoded data. 79 bytes by default.
bufferSize	Data buffer size. If buffer size smaller than required, buffer will be filled with fewer parameters.
mask	Parameters mask - pointer to VSourceParamsMask structure. VSourceParamsMask (declared in VSource.h file) determines flags for each field (parameter) declared in VSourceParams class. If the user wants to exclude any parameters from serialization, he can put a pointer to the mask. If the user wants to exclude a particular parameter from serialization, he should set the corresponding flag in the VSourceParamsMask structure.

VSourceParamsMask structure declaration:

struct VSourceParamsMask
{
    bool logLevel{true};
    bool width{true};
    bool height{true};
    bool gainMode{true};
    bool gain{true};
    bool exposureMode{true};
    bool exposure{true};
    bool focusMode{true};
    bool focusPos{true};
    bool cycleTimeMks{true};
    bool fps{true};
    bool isOpen{true};
    bool roiX{true};
    bool roiY{true};
    bool roiWidth{true};
    bool roiHeight{true};
    bool custom1{true};
    bool custom2{true};
    bool custom3{true};
};

Example without parameters mask:

// Prepare random params.
VSourceParams in;
in.initString = "any string";
in.logLevel = 0;

// Encode data.
uint8_t data[1024];
int size = 0;
in.encode(data, 1024, size);
cout << "Encoded data size: " << size << " bytes" << endl;

Example without parameters mask:

// Prepare random params.
VSourceParams in;
in.initString = "any string";
in.logLevel = 0;

// Prepare params mask.
VSourceParamsMask mask;
mask.logLevel = false; // Exclude logLevel. Others by default.

// Encode data.
uint8_t data[1024];
int size = 0;
in.encode(data, 1024, size, &mask);
cout << "Encoded data size: " << size << " bytes" << endl;

Deserialize video source params

VSourceParams class provides method decode(…) to deserialize video source params (fields of VSourceParams class, see Table 4). Deserialization of video source params necessary in case when you need to receive video source params via communication channels. Method doesn’t decode fields: initString and fourcc. Method automatically recognizes which parameters were serialized by encode(…) method. Method declaration:

bool decode(uint8_t* data, int dataSize);

Parameter	Value
data	Pointer to encode data buffer. Data size should be at least 62 bytes.
dataSize	Size of data.

Returns: TRUE if data decoded (deserialized) or FALSE if not.

Example:

// Encode data.
VSourceParams in;
uint8_t data[1024];
int size = 0;
in.encode(data, 1024, size);

cout << "Encoded data size: " << size << " bytes" << endl;

// Decode data.
VSourceParams out;
if (!out.decode(data, size))
    cout << "Can't decode data" << endl;

Read params from JSON file and write to JSON file

VSource library depends on ConfigReader library which provides method to read params from JSON file and to write params to JSON file. Example of writing and reading params to JSON file:

// Write params to file.
VSurceParams in;
cr::utils::ConfigReader inConfig;
inConfig.set(in, "vSourceParams");
inConfig.writeToFile("TestVSourceParams.json");

// Read params from file.
cr::utils::ConfigReader outConfig;
if(!outConfig.readFromFile("TestVSourceParams.json"))
{
    cout << "Can't open config file" << endl;
    return false;
}

TestVSourceParams.json will look like:

{
    "vSourceParams": {
        "custom1": 150.0,
        "custom2": 252.0,
        "custom3": 30.0,
        "exposureMode": 226,
        "focusMode": 89,
        "fourcc": "skdfjhvk",
        "fps": 206.0,
        "gainMode": 180,
        "height": 61,
        "logLevel": 17,
        "roiHeight": 249,
        "roiWidth": 167,
        "roiX": 39,
        "roiY": 223,
        "source": "alsfghljb",
        "width": 35
    }
}

Build and connect to your project

Typical commands to build VSourceV4L2 library:

cd VSourceV4L2
mkdir build
cd build
cmake ..
make

If you want connect VSourceV4L2 library to your CMake project as source code you can make follow. For example, if your repository has structure:

CMakeLists.txt
src
    CMakeList.txt
    yourLib.h
    yourLib.cpp

Create folder 3rdparty in your repository. Copy repository folder VSourceV4L2 to 3rdparty folder. New structure of your repository:

CMakeLists.txt
src
    CMakeList.txt
    yourLib.h
    yourLib.cpp
3rdparty
    VSourceV4L2

Create CMakeLists.txt file in 3rdparty folder. CMakeLists.txt should contain:

cmake_minimum_required(VERSION 3.13)

################################################################################
## 3RD-PARTY
## dependencies for the project
################################################################################
project(3rdparty LANGUAGES CXX)

################################################################################
## SETTINGS
## basic 3rd-party settings before use
################################################################################
# To inherit the top-level architecture when the project is used as a submodule.
SET(PARENT ${PARENT}_YOUR_PROJECT_3RDPARTY)
# Disable self-overwriting of parameters inside included subdirectories.
SET(${PARENT}_SUBMODULE_CACHE_OVERWRITE OFF CACHE BOOL "" FORCE)

################################################################################
## CONFIGURATION
## 3rd-party submodules configuration
################################################################################
SET(${PARENT}_SUBMODULE_VSOURCE_V4L2                    ON  CACHE BOOL "" FORCE)
if (${PARENT}_SUBMODULE_VSOURCE_V4L2)
    SET(${PARENT}_VSOURCE_V4L2                          ON  CACHE BOOL "" FORCE)
    SET(${PARENT}_VSOURCE_V4L2_TEST                     OFF CACHE BOOL "" FORCE)
    SET(${PARENT}_VSOURCE_V4L2_EXAMPLE                  OFF CACHE BOOL "" FORCE)
endif()

################################################################################
## INCLUDING SUBDIRECTORIES
## Adding subdirectories according to the 3rd-party configuration
################################################################################
if (${PARENT}_SUBMODULE_VSOURCE_V4L2)
    add_subdirectory(VSourceV4L2)
endif()

File 3rdparty/CMakeLists.txt adds folder VSourceV4L2 to your project and excludes test application (VSourceV4L2 class test applications) from compiling (by default test application and example excluded from compiling if VSourceV4L2 included as sub-repository). Your repository new structure will be:

CMakeLists.txt
src
    CMakeList.txt
    yourLib.h
    yourLib.cpp
3rdparty
    CMakeLists.txt
    VSourceV4L2

Next you need include folder 3rdparty in main CMakeLists.txt file of your repository. Add string at the end of your main CMakeLists.txt:

add_subdirectory(3rdparty)

Next you have to include VSourceV4L2 library in your src/CMakeLists.txt file:

target_link_libraries(${PROJECT_NAME} VSourceV4L2)

Done!

Simple example

Example shows how to initialize video source with generic VSource interface and how to capture video in loop. Also example show how to get parameter value (video capture cycle time). Example:

#include <iostream>
#include "VSourceV4L2.h"

int main(void)
{
    // Init video source.
    cr::video::VSource* source = new cr::video::VSourceV4L2();
    std::string initString = "/dev/video0";
    if (!source->openVSource(initString))
        return -1;

    // Main loop.
    cr::video::Frame frame;
    while (true)
    {
        // Wait new frame 1 sec.
        if (!source->getFrame(frame, 1000))
            continue;

        std::cout << "New frame " << frame.frameId <<
        " (" << frame.width << "x" << frame.height << ") cycle time : " <<
        (int)source->getParam(cr::video::VSourceParam::CYCLE_TIME_MKS) <<
        " mksec" << std::endl; 
    }
    
    return 1;
}

Test application

Test application VSourceV4L2Test designed to check how VSourceV4L2 library works. The application allows user to set the resolution, fps and pixel format for video source initialization. The application requires OpenCV libraries installed and user interface in order to show video. If the user has selected video display mode, the application allows to control the exposure mode (manual, auto, shutter priority, aperture priority), focus mode (manual, auto) and gain mode (manual auto) using the keypad and trackbar buttons. The user can also control exposure level, gain level and focus position by trackbars if the video source supports such functions. The application shows the exposure mode, exposure level, gain mode, gain level, focus mode and focus position on the video. If the mode without video display is selected, the application shows the frame index, frame sizes, the time between two video frames, and current fps. For instance;

[35] 1280x720 | 33.589 msec | fps : 29.7717
[36] 1280x720 | 34.416 msec | fps : 29.0563
[37] 1280x720 | 36.439 msec | fps : 27.4431

To run application use command:

./VSourceV4L2Test

After start the application shows information about available video devices in the system:

========================================
VSourceV4L2 v2.1.5 test
========================================
bcm2835-codec-decode (platform:bcm2835-codec):
        /dev/video10
        ...
        /dev/media2

bcm2835-isp (platform:bcm2835-isp):
        /dev/video13
        ...
        /dev/media3

mmal service 16.1 (platform:bcm2835_v4l2-0):
        /dev/video0

rpivid (platform:rpivid):
        /dev/video19
        /dev/media1

Afterwards user should set device name, video width, video height, fps, pixel format and display mode (y/n):

========================================
Set device name (1 - for default /dev/video0): /dev/video0
Set frame width (0 for auto detection): 1280
Set frame height (0 for auto detection): 720
Set fps (0 for auto detection): 30
Set pixel format (BGR24,RGB24,YUV24,GRAY,UYVY,YUYV,NV12,NV21,YV12,YU12): YUYV
Show video (y/n):

If display video mode chose the user can control video source parameters by keyboard:

Table 1 - Control buttons. English layout should be active without CapsLock mode.

Button	Description
ESC	Exit application.
1	Set manual exposure mode.
2	Set auto exposure mode.
3	Set shutter priority exposure mode.
4	Set aperture priority exposure mode.
5	Set manual gain mode.
6	Set auto gain mode.
7	Set manual focus mode.
8	Set auto focus mode.