Snapshotting frames from a playbin instance

[Thiago Santos]

On 08/19/2015 05:35 PM, James Felix Black wrote:
> 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.
Well, it would be nice to debug your case as well to understand what was 
wrong as it seems like it should work. Can you please get a GST_DEBUG=6 
and attach to a bug in bugzilla.gnome.org under GStreamer?

Thanks!
> 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
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-- 
Thiago Sousa Santos
Senior Multimedia Engineer, Open Source Group
Samsung Research America - Silicon Valley

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