How to know that playbin2 can't play video format?

[Jim Norton]

Greetings,

I have a small GTK gstreamer application based on tutorials and sample  
code that works using playbin2. However, if I set the playbin2 uri to  
a file that contains a video and audio stream in which a gstreamer  
plugin exists only to play the audio I end up with an empty video  
window that displays no video while the sound is playing. How do I  
detect at runtime in C code that a either the audio or video portion  
of a stream is unable to be played?

Regards,
Jim