Snapshotting frames from a playbin instance

[James Felix Black]

I ran at DEBUG 2 and didn't get much interesting info., but I also just
wrote something to read the raw RGBA frame sample data and now I can
point OpenCV at that.

Cheers.


On Wed, Aug 19, 2015, at 16:19, Thiago Santos wrote:
> On 08/19/2015 03:46 PM, James Felix
      Black wrote:
>> On Wed, Aug 19, 2015, at 13:52, Thiago Santos wrote:
>>> On 08/19/2015 02:42 PM, James Felix Black wrote:
>>>> Linux ARM (nVidia Jetson TK1), gstreamer-1.5.2, Qt 5.5,
            qt-streamer 1.2.0
>>>>
>>>> I have a simple X11 application that I'm working, based
            for now on the qt-gstreamer demo code [1] that plays a video
            to the screen, and snapshots "interesting" frames to disk.
            I'm using Qt and the qt-gstreamer package, and I am able to
            access sample data directly off the pipeline (using the
            "sample" property at a given time), and write the raw video
            to disk as such:
>>>>
>>>> QGlib::Value val = pipeline->property("sample");  GstSample * v =
>>>> (GstSample *)g_value_get_boxed(val);
>>>>
>>>> // write the contents of v's memory buffer to disk
              ....
>>>>
>>>> What I get is a raw file of 4bytes * 1920 * 1080.
              That's cool! But what I want to do is:
>>>>
>>>> GstCaps * jpegCaps =
              gst_caps_new_simple("image/jpeg", "width", G_TYPE_INT,
              640, NULL);
>>>> GError * err;  GstSample * jpeg = gst_video_convert_sample(v,
              jpegCaps, 100, &err);
>>>>
>>>> ... and then write the contents of *that* sample to
              disk, instead. However, if I do that conversion, jpeg is
              null and the error is:
>>>>
>>>> "Cannot find any image encoder for caps image/jpeg"
>>>>
>>>> OK, that seems fair. But my pipeline (again see the
              example code at [1]) is constructed as such:
>>>>
>>>> m_pipeline =
QGst::ElementFactory::make("playbin").dynamicCast<QGst::Pipeline>();
>>>>
>>>> My question then becomes: how should I approach this
              problem? Should I modify the pipeline? I see that there's
              a "convert-sample" signal on playbin;  is that what I
              should be using?
>>>>
>>>> Any light anyone can shed would be most welcome.
>>>
>>> Do you have jpegenc (or any other jpeg encoder) in your
          system? gst-inspect-1.0 jpegenc should show it. Or gst-inspect-
          1.0 |grep jpeg.
>>>
>>
>> I was missing jpegenc; thanks. Having installed it, I now get
        an "Internal data flow error".
>> default
          convertframe.c:325:gst_video_convert_sample: Could not convert
          video frame: Internal data flow error.


>> This is using a one-second timeout on the frame conversion
        (GST_SECOND). Hmmm. Any pointers here?
> I'd recommend using GST_DEBUG to get some log and check what exactly
    was the error.
>
>
>>
>>
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>
>
> --
Thiago Sousa Santos Senior Multimedia Engineer, Open Source Group
Samsung Research America - Silicon Valley
> _________________________________________________
> gstreamer-devel mailing list gstreamer-devel at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/gstreamer-devel
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