QT 4.4 / Phonon / Video / Rendering a single frame

[rextr]

Hi, Is there any way to get individual frames of a video and render it as an image file?

What I want to do is a video preview image(a jpg file for example) which gives an idea of what the video is about, like youtube preview.

I'm pretty new to Qt Jambi and Phonon videoplayer, I have searched the API docs but still can't figure it out , any help will be appreciated, thanks ...

[aamer4yu]

Am not sure too.

But u can try this -
Pause the VideoPlayer / VideoWidget when u show the application.
Its like seeking to frame 0 or time 0 and pausing. This will show the first frame.
Then u can proceed with the play function

hope i made sense :P

[tituslup]

hello,
I 'm also trying to get an image from a videostream, i thought of using grabWidget on the video widget but it doesn't seem to capture anything from the video. I also tried to use pause on the media object, grab , then play (as suggested ).
If anyone knows how to capture a frame please reply.

Thank you,
Titus

Edited:
Nevermind, it works just fine, it didn't like the place i made the videoWidget.

[JimDaniel]

What do you mean by "didn't like the place I made the widget?" I'm trying to accomplish the same thing, but as of yet have not gotten it to work. All I get is a gray box the size of the widget. Thanks for any help you can give...

[tituslup]

Hello JimDaniel,

sorry for taking so long to answer you. I'll give you an example how i used the video Widget and the grabWidget:

// this code is inside a class that inherits a QWidget
m_MediaObject = new Phonon::MediaObject(this);
m_MediaObject->clearQueue ();
m_MediaObject->enqueue(Phonon::MediaSource(fileName)); // or setCurrentSource
m_MediaObject->play();
 
 
m_videoWidget = new Phonon::VideoWidget(this);
m_videoWidget->setGeometry(0,0,500,500);
Phonon::createPath(m_MediaObject, m_videoWidget);
 
m_videoWidget = new Phonon::VideoWidget(this);
m_videoWidget->setGeometry(500,500,500,500);
Phonon::createPath(m_MediaObject, m_videoWidget);
 
// if you want to grab the entire window
//QPixmap ecran = QPixmap::grabWindow(QApplication::desktop()->winId());
QPixmap image= QPixmap::grabWidget(this);
image.save("printScreen.bmp");

// this code is inside a class that inherits a QWidget
m_MediaObject = new Phonon::MediaObject(this);
m_MediaObject->clearQueue ();
m_MediaObject->enqueue(Phonon::MediaSource(fileName)); // or setCurrentSource
m_MediaObject->play();


m_videoWidget = new Phonon::VideoWidget(this);
m_videoWidget->setGeometry(0,0,500,500);
Phonon::createPath(m_MediaObject, m_videoWidget);

m_videoWidget = new Phonon::VideoWidget(this);
m_videoWidget->setGeometry(500,500,500,500);
Phonon::createPath(m_MediaObject, m_videoWidget);

// if you want to grab the entire window
//QPixmap ecran = QPixmap::grabWindow(QApplication::desktop()->winId());
QPixmap image= QPixmap::grabWidget(this);
image.save("printScreen.bmp");

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Now, the thing is that i put there two video widgets, because for some reason i cant grab anything from the first one .The second one works fine, and i can grab the widget(image) and save it to a file or work with ... When the two videoWidgets are playing side by side, as in the case above, the video inside them is scaled differently in the widgets.

I hope this helps you.

[JuanC]

Now, the thing is that i put there two video widgets, because for some reason i cant grab anything from the first one .The second one works fine, and i can grab the widget(image) and save it to a file or work with ... When the two videoWidgets are playing side by side, as in the case above, the video inside them is scaled differently in the widgets.

I think there is a bug , you should submit a report about it :
http://trolltech.com/trolltech/bugreport-form

[JimDaniel]

Thanks for responding. That does seem like a bug, but good you got it to work. I'll give it a try.

Frustrated with the (current) limitations of phonon, I've decided to roll my own video class using the ffmpeg api. Its nearly done. When I'm finished I'll post it here in case anyone else wants to use it.

[goulart81]

Please do. I am also looking to capture individual frames from a video file.

[jftaylor21]

I would also be interested in it.

[DanR]

For my projects I also need individual frame decoding, and also video encoding.

Eventually, I wrote an FFmpeg wrapper for QT4. You can find it here: http://code.google.com/p/qtffmpegwrapper

It provides two classes: QVideoEncoder and QVideoDecoder. Frames are passed as QImage to/from the encoder/decoder. Any video format supported by FFmpeg is supported.

There could be a few more exposed functions, but for me it does the job.

Modified BSD license.

[xairoy]

Hi ,
I was trying to your code. I have Window XP and I am using Visial Studio 2005. I can build the soluton but when try to run the code, i get the following exception after this line in your QVideoDecoder.cpp. :
ffmpeg::avcodec_init();
Unhandled exception at 0x00011714 in QTVIDEOWRAPPER.exe: 0xC0000096: Privileged instruction.

Please help. It will very useful for me if I can compile and run it properly.
Thanks.
Roy