Grabbing video frames via Appsink

Fri Aug 1 08:17:18 PDT 2014

when you download gst-plugins-base source you can find in
tests/examples/app example app which use both appsink and appsrc.
Dňa 01.08.2014 o 17:04 Lasse Laursen napísal(a):
> Not quite sure what you mean by -
>
> 'check in which state return gst_element_get_state()'?
what is in "state" variable after gst_element_get_state()
>
> But to clarify, no - none of the callback functions are ever called.
> The pipeline just doesn't seem to start.
>
> Regards,
> Lasse
>
> On 01-08-2014 23:48, Dušan Poizl wrote:
>> GST_STATE_CHANGE_ASYNC is ok. it means that pipeline doesn't finished
>> changing state before gst_element_set_state() return. whole pipeline
>> run in separate thread. when you get state you practically wait until
>> pipeline finish transition to desired state. so check in which state
>> return gst_element_get_state() and does your callbacks end up called?
>>
>> Dňa 01.08.2014 o 14:37 Lasse Laursen napísal(a):
>>> Hey Dev's,
>>>
>>> I've been throwing myself at this problem for a few days without any
>>> significant progress. Hopefully someone can tell me what painfully
>>> obvious part I've overlooked.
>>>
>>> Essentially what I'm trying to do is just grab some frames of video
>>> during playback from an appsink, but it seems my simple pipeline is
>>> missing something vital, because when I get to changing the state to
>>> 'paused' or 'playing' the GstStateChangeReturn I recieve is
>>> 'GST_STATE_CHANGE_ASYNC (2)'. The debug log doesn't yield any error
>>> output, so I'm a bit unsure of what to look closer at?
>>>
>>> Have I perhaps not hooked something up correctly? What am I missing
>>> here?
>>>
>>> Below is my simple code for trying to hook up this simple pipeline
>>> and grab some frames.
>>>
>>> ---------
>>>
>>>     std::string launchString = "uridecodebin uri=" + mVideoFileName
>>> + " ! appsink name=sink";
>>>
>>>     mGstPipeline = gst_parse_launch( launchString.c_str(), &pstGErr1 );
>>>     printErrorToConsole( pstGErr1 != nullptr, "GStreamer Error:
>>> Could not construct pipeline", pstGErr1 );
>>>
>>>
>>>     GstElement *mPipeline_AppSink;
>>>     mPipeline_AppSink = gst_bin_get_by_name( GST_BIN( mGstPipeline
>>> ), "sink" );
>>>
>>>    
>>> //////////////////////////////////////////////////////////////////////////
>>> VIDEO SINK
>>>     // Config Video Sink
>>>     gst_base_sink_set_sync( GST_BASE_SINK( mPipeline_AppSink ), true );
>>>     gst_app_sink_set_max_buffers( GST_APP_SINK( mPipeline_AppSink ),
>>> 8 );
>>>     gst_app_sink_set_drop( GST_APP_SINK( mPipeline_AppSink ), true );
>>>     gst_base_sink_set_max_lateness( GST_BASE_SINK( mPipeline_AppSink
>>> ), -1 );
>>>
>>>     // Set some fix caps for the video sink
>>>     // It would seem that GStreamer then tries to transform any
>>> incoming video stream according to these caps
>>>     GstCaps* caps = gst_caps_new_simple( "video/x-raw-rgb",
>>>         "bpp", G_TYPE_INT, 24,
>>>         "depth", G_TYPE_INT, 24,
>>>         "endianness", G_TYPE_INT, 4321,
>>>         "red_mask", G_TYPE_INT, 0xff0000,
>>>         "green_mask", G_TYPE_INT, 0x00ff00,
>>>         "blue_mask", G_TYPE_INT, 0x0000ff,
>>>         "alpha_mask", G_TYPE_INT, 0x000000ff,
>>>         NULL );
>>>
>>>     gst_app_sink_set_caps( GST_APP_SINK( mPipeline_AppSink ), caps );
>>>     gst_caps_unref( caps );
>>>
>>>     // Set the configured video appsink to the main pipeline
>>>     //g_object_set( m_GstPipeline, "video-sink", m_GstVideoSink,
>>> (void*) NULL );
>>>
>>>     // Tell the video appsink that it should not emit signals as the
>>> buffer retrieving is handled via callback methods
>>>     g_object_set( mPipeline_AppSink, "emit-signals", false, "sync",
>>> true, (void*) NULL );
>>>
>>>     GstAppSinkCallbacks cbs; // Does this need to be kept alive?
>>>
>>>     // Set Video Sink callback methods
>>>     cbs.eos = &GSCinderApp::onEosFromVideoSource;
>>>     cbs.new_preroll = &GSCinderApp::onNewPrerollFromVideoSource;
>>>     cbs.new_sample = &GSCinderApp::onNewBufferFromVideoSource;
>>>     gst_app_sink_set_callbacks( GST_APP_SINK( mPipeline_AppSink ),
>>> &cbs, this, NULL );
>>>
>>>
>>>    
>>> //////////////////////////////////////////////////////////////////////////
>>> BUS
>>>     // Set GstBus
>>>     //m_GstBus = gst_pipeline_get_bus( GST_PIPELINE( m_GstPipeline ) );
>>>
>>>     if ( mGstPipeline != NULL )
>>>     {
>>>         // We need to stream the file a little bit in order to be
>>> able to retrieve information from it
>>>         GstStateChangeReturn nStateChgRet;
>>>
>>>         nStateChgRet = gst_element_set_state( mGstPipeline,
>>> GST_STATE_READY );
>>>         printErrorToConsole( nStateChgRet ==
>>> GST_STATE_CHANGE_FAILURE, "GStreamer Error: State Change Failure 1" );
>>>
>>>         nStateChgRet = gst_element_set_state( mGstPipeline,
>>> GST_STATE_PAUSED );
>>>         printErrorToConsole( nStateChgRet ==
>>> GST_STATE_CHANGE_FAILURE, "GStreamer Error: State Change Failure 1" );
>>>
>>>         // For some reason this is needed in order to gather video
>>> information such as size, framerate etc ...
>>>         GstState state;
>>>         gst_element_get_state( mGstPipeline, &state, NULL, 2 *
>>> GST_SECOND );        // Erm... Why get state?
>>>
>>>     }
>>>     else {
>>>         printErrorToConsole( true, "GStreamer Error: Pipeline
>>> Empty?!" );
>>>     }
>>>
>>>     // Retrieve and store all relevant Media Information
>>>     //retrieveVideoInfo();
>>>
>>>     // Check if we actually end up playing?
>>>     if ( mGstPipeline != NULL )
>>>     {
>>>         GstStateChangeReturn nStateChgRet;
>>>         nStateChgRet = gst_element_set_state( mGstPipeline,
>>> GST_STATE_PAUSED );
>>>         printErrorToConsole( nStateChgRet ==
>>> GST_STATE_CHANGE_FAILURE, "GStreamer Error: State Change Failure 3" );
>>>
>>>     }
>>>     else {
>>>         printErrorToConsole( true, "GStreamer Error: Pipeline
>>> Empty?!" );
>>>     }
>>>
>>> ----------------
>>>
>>> Regards,
>>> Lasse
>>>
>>> -- 
>>> Lasse Farnung Laursen
>>> Post.doc at the University of Tokyo
>>> www.lasselaursen.com <http://www.lasselaursen.com>
>>> FB: lasse.laursen <https://www.facebook.com/lasse.laursen>
>>> Twitter: @PMP_J <https://twitter.com/PMP_J>
>>>
>>>
>>> _______________________________________________
>>> gstreamer-devel mailing list
>>> gstreamer-devel at lists.freedesktop.org
>>> http://lists.freedesktop.org/mailman/listinfo/gstreamer-devel
>>
>>
>>
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>> http://lists.freedesktop.org/mailman/listinfo/gstreamer-devel
>
> -- 
> Lasse Farnung Laursen
> Post.doc at the University of Tokyo
> www.lasselaursen.com <http://www.lasselaursen.com>
> FB: lasse.laursen <https://www.facebook.com/lasse.laursen>
> Twitter: @PMP_J <https://twitter.com/PMP_J>
>
>
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> gstreamer-devel at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/gstreamer-devel

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