Snapshotting frames from a playbin instance

[James Felix Black]

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?
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