Counting video frames

[Darren Staples]

I’ve come across a problem processing individual frames of a movie using the appsrc component.

The code in my main loop looks something like this:

if ( !g_queue_is_empty( GST_APP_SINK( sink )->queue ))
  {
    // Get access to raw frame buffer
    GstBuffer *buff = gst_app_sink_pull_buffer( GST_APP_SINK( sink ));
    if ( buff )
    {            
      // Get pointer to frame data
      guint8 *buff_data = (guint8 *)GST_BUFFER_DATA( buff );

      // Do something with buffer here
      
      // Release buffer  
      gst_buffer_unref( buff );
      buff = NULL;

      num_frames++;    
    }
 }

This works, but if I run it a few times, using the same video each time, I sometimes see that the number of frames processed is lower than expected. This happens maybe once in five runs.
I used a gst_app_sink_set_drop( sink , false ) to ensure that the pipeline stalls if I don’t pull buffers quickly enough.

Any ideas why or where I might be dropping frames ?

On a similar topic, is there a mechanism within Gstreamer for identifying the number of frames in a movie file ?

Thanks !

Darren

 

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