PARP Research Group University of Murcia


QVMPlayerReaderBlock Class Reference
[Block programming]

Class to create MPlayer input video reader block components. More...

#include <QVMPlayerReaderBlock>

Inherits QVVideoReaderBlock.

List of all members.

Public Member Functions

 QVMPlayerReaderBlock (QString name)
 Constructor for QVMPlayerReaderBlock class.
 ~QVMPlayerReaderBlock ()
 Destructor for QVMPlayerReaderBlock class.

Protected Member Functions

bool open (QString urlName, int &cols, int &rows, int &fps)
 Pure virtual open method.
void close ()
 Pure virtual close method.
bool grab (QVImage< uChar, 1 > &imgY, QVImage< uChar, 1 > &imgU, QVImage< uChar, 1 > &imgV)
 Pure virtual grab method.
double lengthOfVideo ()
 Pure virtual method to get the length of the video.
double currentPos ()
 Pure virtual method to get the current time position in the video.


Detailed Description

Class to create MPlayer input video reader block components.

This is an implementation of the class QVVideoReaderBlock based on the QVMPlayerReader interface class for the MPlayer application (see QVVideoReaderBlock documentation for more details on generic camera blocks). Specifically, this mplayer camera block can create input blocks to read frames from a video source in a QVision application. The video sources can be any video file or device connected physically to the computer, or remotely through a network video stream. The class can read from a wide variety of media formats.

For a detailed usage of block programming and the use of this class in a block-oriented application, see section Creating the first block-oriented application. To learn how to specify a given video source for the class, read QVMPlayerReader class documentation. Specifically, the Video source identifier URL formats section.

To use it, create a QVMPlayerReaderBlock object in the main function, and link a gray image, a RGB image, or three (Y,U,V) one channel images from a block. For example:

int main(int argc, char *argv[])
        {
        [...]
        // The following block should have a property named 'Output image' containing a gray (QVImage<uChar>) or 
        // (QVImage<uChar,3>) RGB image:
        MyBlock myBlock("My block");
        [...]
        QVMPlayerReaderBlock camera("Input camera");
        camera.linkProperty(&myBlock, "Input image");
        [...]
        }

Alternatively you can link simultaneously three properties containing the Y, U and V channels of the images grabbed by the camera:

int main(int argc, char *argv[])
        {
        [...]
        // The following block should have three QVImage<uChar,1> properties named 'Input image Y', 'Input image U',
        // and 'Input image V':
        MyBlock myBlock("My block");
        [...]
        QVMPlayerReaderBlock camera("Input camera");
        camera.linkProperty(&myBlock, "Input image Y", "Input image U", "Input image V");
        [...]
        }

Input properties are the following:

  • NoLoop (bool): If the MPlayer camera should be opened in no loop mode.
  • RealTime (bool): If the MPlayer camera should be opened in real time mode.
  • Deinterlaced (bool): If the MPlayer camera should deinterlace (using median filter) the video.
  • URL (QString): URL (see QVMPlayerReader ) of the video file to read.
  • Cols (int): Number of suggested columns for the video source.
  • Rows (int): Number of suggested rows for the video source.

Note.- RealTime property is also input (and as such can be initialized using the command line), but invisible to the GUI (because once the camera has been linked, it cannot be relinked changing its synchronism).

Note.- Note that you can open the camera in a different size of that specified in the real video source file (this class will automatically rescale output images if needed).

Output properties are the following:

  • Opened (bool): Tells if the camera is correctly opened and working.
  • FPS (int): FPS of the video.
  • Frames (int): Number of read frames up to now.
  • ColsR (int): Actual number of columns of the video -not necessarily equal to the number of requested columns, which will in any case be transparently rounded to the nearest upper even integer-.
  • RowsR (int): Actual number of rows of the video -not necessarily equal to the number of requested rows, which will in any case be transparently rounded to the nearest upper even integer-.
  • Pos (double): Current position in the video, if available (in seconds).
  • Length (double): Length of the video, if available (in seconds).

Note.- Remember that you can open the camera in a different size of that specified in the real video source file (this class will automatically rescale output images if needed); thus, ColsR and RowsR will always contain the real size of the output images served by this block.

Output image properties:

  • RGB image (QVImage<uChar,3>): Last grabbed RGB image.
  • Y channel image (QVImage<uChar,1>): Last grabbed Y channel image.
  • U channel image (QVImage<uChar,1>): Last grabbed U channel image.
  • V channel image (QVImage<uChar,1>): Last grabbed V channel image.

Output image properties can (and should!) be linked automatically, without the need of naming them explicitly, using any of the QVVideoReaderBlock::linkProperty() available methods.

You can specify any of the input properties at the start of the program, using the command line parameters; for example, the file to read the video from can be specified by calling the program this way: ./program --File="/home/me/myfile.avi". But modification of these properties can also be done directly in the corresponding graphical widgets when reopening the camera during execution (though, of course, these new values will have no effect until the camera is reopened).

Two important properties are RealTime and NoLoop, both boolean. The first one specifies if the camera will be read in real time mode -possibly leaving frames unprocessed, if processing is slower than reading- (RealTime=true), or at maximum speed -but without leaving any frame unprocessed in any case- (RealTime=false). The second one specifies if the camera will be closed when the end of the file is reached (NoLoop=true), or will loop, starting from the first frame again and again (NoLoop=false).

See also:
QVMPlayerReader

Definition at line 118 of file qvmplayerreaderblock.h.


Constructor & Destructor Documentation

QVMPlayerReaderBlock::QVMPlayerReaderBlock ( QString  name  ) 

Constructor for QVMPlayerReaderBlock class.

Parameters:
name the (optional) name given to the camera block.

Definition at line 30 of file qvmplayerreaderblock.cpp.


Member Function Documentation

bool QVMPlayerReaderBlock::open ( QString  urlName,
int &  cols,
int &  rows,
int &  fps 
) [protected, virtual]

Pure virtual open method.

Reimplementations of this method should open the video source specified by the string urlName, trying to open it with the suggested cols, rows and fps. The method must indicate a successful opening by returning true (and updating the corresponding cols, rows and fps output values to the really obtained ones, which could coincide or not with the suggested input values), or false, if there was any problem opening the source.

Parameters:
urlName QString determining the video source.
cols Suggested number of columns (as input). On return contains real number of columns (as output).
rows Suggested number of rows (as input). On return contains real number of rows (as output).
fps Suggested fps (as input). On return contains real fps (as output).
Returns:
true if success, false if fail.

Implements QVVideoReaderBlock.

Definition at line 37 of file qvmplayerreaderblock.cpp.

void QVMPlayerReaderBlock::close (  )  [protected, virtual]

Pure virtual close method.

Reimplementations of this method should close the video source.

Implements QVVideoReaderBlock.

Definition at line 67 of file qvmplayerreaderblock.cpp.

bool QVMPlayerReaderBlock::grab ( QVImage< uChar, 1 > &  imgY,
QVImage< uChar, 1 > &  imgU,
QVImage< uChar, 1 > &  imgV 
) [protected, virtual]

Pure virtual grab method.

Reimplementations of this method should grab Y, U and V channel images in the corresponding variable parameters, with respective sizes cols x rows, cols/2 x rows/2 and cols/2 x rows/2 (with cols and rows as returned by the open() method), returning true if grabbing was succesful, or false otherwise (for example, if the camera was closed).

Parameters:
imgY On return, contains the grabbed Y image.
imgU On return, contains the grabbed U image.
imgV On return, contains the grabbed V image.

Implements QVVideoReaderBlock.

Definition at line 72 of file qvmplayerreaderblock.cpp.

double QVMPlayerReaderBlock::lengthOfVideo (  )  [protected, virtual]

Pure virtual method to get the length of the video.

Reimplementations of this method should inform of the length of the video in seconds. A length equal to 0.0 should be returned if not available (for example, for live cameras, remote streaming video, and the like)

Implements QVVideoReaderBlock.

Definition at line 77 of file qvmplayerreaderblock.cpp.

double QVMPlayerReaderBlock::currentPos (  )  [protected, virtual]

Pure virtual method to get the current time position in the video.

Reimplementations of this method should inform of the current position in the video in seconds.

Implements QVVideoReaderBlock.

Definition at line 82 of file qvmplayerreaderblock.cpp.


The documentation for this class was generated from the following files:



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