Re: Gstreamermm Spectrum Plugin

[Cole Bush <bush c husky neu edu>]

So if I have the bus receiving messages from spectrum, would i get the "magnitude" of the FFT with message->get_structure()->get_field("magnitude", mags_by_ref)?

Thanks!

On Wed, Apr 13, 2016 at 7:30 PM, Marcin Kolny <marcin kolny gmail com> wrote:

2016-04-14 1:09 GMT+02:00 Cole Bush <bush c husky neu edu>:

Hello,

I am creating a gstreamermm pipeline that uses the "good" spectrum plugin to perform a fft on the audio. I think I have the pipeline working correctly (it plays the file) and I am recieving messages on the bus, but I don't know how to get the information from it. Firstly, is this the correct way to initialize it?

     Glib::RefPtr<Element> spectrum;

     spectrum = ElementFactory::create_element("spectrum");

     spectrum->property("post-messages", true);

     spectrum->property("bands", 20);

     spectrum->property("threshold", -80);

Should it be a RefPtr to an Element or AudioFilter? 

It can be either Element or AudioFilter. As long as you don't need any AudioFilter-specific feature, you can use Element class.
 

Second, in my bus message listener I have a case for a message type of Gst::MESSAGE_ELEMENT which then calls a function to get the info: "decode_spectrum(const RefPtr<Message> &message);" How do I get info like the name (should be "spectrum")

Since you didn't specify element name in your code, it'll be autogenerated and you can get the name by calling:

  spectrum->get_name();

If you want to explicitly specify the name, you should use method: https://developer.gnome.org/gstreamermm/stable/classGst_1_1ElementFactory.html#a6a85a2a3c4f69383cad2686d381e10e9

 

and the data (magnitude in dB)?

You'd have to use Gst::Structure::get_field() method.

Thanks for any insight!

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Best regards,
Marcin Kolny