Getting converted frame from playbin2 element

[vaisaari]

Hi all,

I'm trying to implement a function that returns the current frame of playbin2 element as a QImage (Qt data type). When I call the function (for the same video), sometimes it works perfectly, sometimes parts of the frame (bottom rows) are missing. What am I doing wrong? Should I somehow be able to wait for the "convert-frame" operation to finish, or what? You can find my example code below. Thank you for your help!
 

QImage Video::getFrame()
{

GstBuffer *buffer;
GstCaps *caps;

caps = gst_caps_new_simple("video/x-raw-rgb","bpp", G_TYPE_INT, 24,"depth", G_TYPE_INT, 24,NULL);

g_signal_emit_by_name(player, "convert-frame", caps, &buffer);

unsigned char* data=(unsigned char *) GST_BUFFER_DATA (buffer);
QImage img(data, width, height, QImage::Format_RGB888);

return img;
}

[Marco Ballesio]

Hi,

On Mon, Jan 3, 2011 at 1:12 PM, vaisaari <[hidden email]> wrote:
>
> Hi all,
>
> I'm trying to implement a function that returns the current frame of
> playbin2 element as a QImage (Qt data type). When I call the function (for
> the same video), sometimes it works perfectly, sometimes parts of the frame
> (bottom rows) are missing. What am I doing wrong? Should I somehow be able
> to wait for the "convert-frame" operation to finish, or what? You can find
> my example code below. Thank you for your help!

imo this should not happen, as the signal handler (delegated to
playsink) internally calls gst_play_sink_get_last_frame, which locks
playsink. Can you post to pastebin the output you get after setting
GST_DEBUG=playsink:5 ?

Which video decoder are you using?

Besides, if you're trying to render a video clip in Qt, you may
consider using QtGStreamer..

Regards

>
>
> QImage Video::getFrame()
> {
>
> GstBuffer *buffer;
> GstCaps *caps;
>
> caps = gst_caps_new_simple("video/x-raw-rgb","bpp", G_TYPE_INT, 24,"depth",
> G_TYPE_INT, 24,NULL);
>
> g_signal_emit_by_name(player, "convert-frame", caps, &buffer);
>
> unsigned char* data=(unsigned char *) GST_BUFFER_DATA (buffer);
> QImage img(data, width, height, QImage::Format_RGB888);
>
> return img;
> }
>
>
> --
> View this message in context: http://gstreamer-devel.966125.n4.nabble.com/Getting-converted-frame-from-playbin2-element-tp3171830p3171830.html
> Sent from the GStreamer-devel mailing list archive at Nabble.com.
>
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[vaisaari]

> imo this should not happen, as the signal handler (delegated to
> playsink) internally calls gst_play_sink_get_last_frame, which locks
> playsink. Can you post to pastebin the output you get after setting
> GST_DEBUG=playsink:5 ?

You can find the output from here . The output looks the same whether or not the conversion is successful.

> Which video decoder are you using?

I have tried it with both uncompressed and MPEG4 encoded videos.

> Besides, if you're trying to render a video clip in Qt, you may
> consider using QtGStreamer..

It looks very promising. At some point, I most certainly will.

[Marco Ballesio]

Hi,

looks like my time machine for jumping 11 days in the future
eventually works.. (lame excuse for my late reply)

Maybe you've already fixed your issue, but I still have a few ideas.

On Mon, Jan 10, 2011 at 4:15 PM, vaisaari <[hidden email]> wrote:
>
>> imo this should not happen, as the signal handler (delegated to
>> playsink) internally calls gst_play_sink_get_last_frame, which locks
>> playsink. Can you post to pastebin the output you get after setting
>> GST_DEBUG=playsink:5 ?
>
> You can find the output from  http://pastebin.com/raw.php?i=HgD1S8Uz here  .
> The output looks the same whether or not the conversion is successful.

yep, it looks good.

>
>> Which video decoder are you using?
>
> I have tried it with both uncompressed and MPEG4 encoded videos.
>
>> Besides, if you're trying to render a video clip in Qt, you may
>> consider using QtGStreamer..
>
> It looks very promising. At some point, I most certainly will.

here:

http://doc.qt.nokia.com/qt-maemo-4.7/qimage.html#QImage-4

is stated the validity of the data into memory must last at least as
long as the QImage itself and in the list you've reported it appears
you're not handling buffer references at all. At best, you're leaking
memory like there's no tomorrow, at worst (depending on the pov) the
buffer "buffer" gets unreffed somewhere by chances and then you might
observed teared images (depending on the color space) or even
segfaults. Another good reason for using QtGstreamer ;)

Even if it worked, I would anyway not use such an approach to convert
all the frames in a clip (check what does the gst_video_convert_frame
function do to be convinced). It's imo better to use a color space
conversion element (e.g. ffmpegcolorspace) at the end of the pipeline
or after a tee and an appsink element.

Regards,
Marco

>
>
> --
> View this message in context: http://gstreamer-devel.966125.n4.nabble.com/Getting-converted-frame-from-playbin2-element-tp3171830p3207234.html
> Sent from the GStreamer-devel mailing list archive at Nabble.com.
>
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