How to get a snapshot of a video in Qt???

[wshn13]

Do someone know how to get a snapshot of a video in Qt?

[Talei]

For video that's not played I can think only of ffmpeg.
For video that's played use Phonon and grabWidget()

[wshn13]

In my program , I can't play it and grabWidget, I must take snapshot in the back,not visible . So how can I achieve?

For video that's not played I can think only of ffmpeg.
For video that's played use Phonon and grabWidget()

In my program , I can't play it and grabWidget, I must take snapshot in the back,not visible . So how can I achieve?

[high_flyer]

You didn't give enough information to answer your question.
Do you have access to the frame data?
If so, its easy.

[robotics]

how about using open cv library??

[Talei]

If You don't want create Your solution, use the ready one, i.e.:
lib: vlc, ffmpeg
another prog.: ffmpeg
For lib go into vlc/ffmpeg page and dll src. But You will face some library licensing restriction.
For ffmpeg use QProcess, send time infromation and output file path.

[stampede]

With OpenCV its just few lines of code (for RGB24 images). This will extract frame number frameNo from video and convert to QImage:

QString pathToVideo = ...
CvCapture * capture = cvCaptureFromAVI( pathToVideo.toAscii(),constData() );
cvSetCaptureProperty(capture, CV_CAP_PROP_POS_FRAMES, frameNo);
IplImage * cvimg = cvQueryFrame(capture);
if(cvimg){ // this will be NULL if you specify invalid frame index
    QImage temp = QImage((const uchar*)cvimg->imageData,cvimg->width,cvimg->height,QImage::Format_RGB888);
    QImage image = temp.rgbSwapped(); // opencv images are BGR
}
cvReleaseCapture(&capture);

QString pathToVideo = ...
CvCapture * capture = cvCaptureFromAVI( pathToVideo.toAscii(),constData() );
cvSetCaptureProperty(capture, CV_CAP_PROP_POS_FRAMES, frameNo);
IplImage * cvimg = cvQueryFrame(capture);
if(cvimg){ // this will be NULL if you specify invalid frame index
    QImage temp = QImage((const uchar*)cvimg->imageData,cvimg->width,cvimg->height,QImage::Format_RGB888);
    QImage image = temp.rgbSwapped(); // opencv images are BGR
}
cvReleaseCapture(&capture);

To copy to clipboard, switch view to plain text mode 

To work with other image formats, you will have to do some direct pixel manipulation.

[wshn13]

If don't use open cv ,just use something in Qt,how can i achieve it?

If You don't want create Your solution, use the ready one, i.e.:
lib: vlc, ffmpeg
another prog.: ffmpeg
For lib go into vlc/ffmpeg page and dll src. But You will face some library licensing restriction.
For ffmpeg use QProcess, send time infromation and output file path.

How can I do just use Qt ?

[Talei]

Well I can't actually post any code for you, but You should look for either libVLC (VideLan - C=code) or AFAIK libavcodec (part of FFmpeg):
http://wiki.videolan.org/LibVLC
http://ffmpeg.org/download.html
use those libraries to retrieve the data.
In case of FFmpeg carefully read license because there is a loot of licensed stuff so ...

Most easiest cross-platform way of doing this task (excluding grabWindow()) is to use ffmpeg. Download ffmpeg (binaries) for Your platform and use QProcess to capture "screenshot" (ffmpeg -s). Then read that file into i.e. QImage and with minimum work You have a screen-shoot taking capable program of the video at particular time (defined earlier)

[wshn13]

Well I can't actually post any code for you, but You should look for either libVLC (VideLan - C=code) or AFAIK libavcodec (part of FFmpeg):
http://wiki.videolan.org/LibVLC
http://ffmpeg.org/download.html
use those libraries to retrieve the data.
In case of FFmpeg carefully read license because there is a loot of licensed stuff so ...

Most easiest cross-platform way of doing this task (excluding grabWindow()) is to use ffmpeg. Download ffmpeg (binaries) for Your platform and use QProcess to capture "screenshot" (ffmpeg -s). Then read that file into i.e. QImage and with minimum work You have a screen-shoot taking capable program of the video at particular time (defined earlier)

Thanks for your suggestion !

---

Added after 33 minutes:

When I ues ffmpeg to take a snapshot in cmdline ,I failed, even I google it ,I still not achieve

[Talei]

Well... check this cmd:

ffmpeg -y -i "f:\path\to\movies" -ss "00:02:12.0" -vcodec mjpeg -vframes 1 -s 1280x720 "c:\picture.jpg"

ffmpeg -y -i "f:\path\to\movies" -ss "00:02:12.0" -vcodec mjpeg -vframes 1 -s 1280x720 "c:\picture.jpg"

To copy to clipboard, switch view to plain text mode 

it's working for me.

[wshn13]

Well... check this cmd:

ffmpeg -y -i "f:\path\to\movies" -ss "00:02:12.0" -vcodec mjpeg -vframes 1 -s 1280x720 "c:\picture.jpg"

ffmpeg -y -i "f:\path\to\movies" -ss "00:02:12.0" -vcodec mjpeg -vframes 1 -s 1280x720 "c:\picture.jpg"

To copy to clipboard, switch view to plain text mode 

it's working for me.

I modify you cmd like this: ffmpeg -y -i "/home/wshn13/MyDocs/Video/a.avi" -ss "00:02:12.0" -vcodec mjpeg -vframes 1 -s 1280x720 "/home/wshn13/picture.jpg"
but a error accur to me says /home/wshn13/MyDocs/Video/a.avi: Invalid data found when processing input
I don't know why