Add example for pad probes

examples/src/bin/pad_probes.rs

@@ -0,0 +1,64 @@
+extern crate gstreamer as gst;
+use gst::*;
+
+use std::u64;
+use std::i16;
+use std::env;
+use std::mem;
+
+fn main() {
+    gst::init().unwrap();
+
+    let pipeline = gst::parse_launch("audiotestsrc name=src ! audio/x-raw,format=S16BE,channels=1 ! fakesink").unwrap();
+    let bus = pipeline.get_bus().unwrap();
+
+    let src = pipeline.clone().dynamic_cast::<Bin>().unwrap().get_by_name("src").unwrap();
+    let src_pad = src.get_static_pad("src").unwrap();
+    src_pad.add_probe(PAD_PROBE_TYPE_BUFFER, |_, probe_info| {
+        if let Some(ref probe_data) = probe_info.data {
+            match *probe_data {
+                PadProbeData::Buffer(ref buffer) => {
+                    let map = buffer.map_read().unwrap();
+                    let data = map.as_slice();
+                    let sum: f64 = data.chunks(2).map(|sample| {
+                        let u: u16 = ((sample[0] as u16) << 8) | (sample[1] as u16);
+                        let f = (u as i16 as f64) / (i16::MAX as f64);
+                        f * f
+                    }).sum();
+                    let rms = (sum / ((data.len() / 2) as f64)).sqrt();
+                    println!("rms: {}", rms);
+                },
+                _ => (),
+            }
+        }
+
+        PadProbeReturn::Ok
+    });
+
+    let ret = pipeline.set_state(gst::State::Playing);
+    assert_ne!(ret, gst::StateChangeReturn::Failure);
+
+    loop {
+        let msg = match bus.timed_pop(u64::MAX) {
+            None => break,
+            Some(msg) => msg,
+        };
+
+        match msg.view() {
+            MessageView::Eos => break,
+            MessageView::Error(err) => {
+                println!(
+                    "Error from {}: {} ({:?})",
+                    msg.get_src().get_path_string(),
+                    err.get_error(),
+                    err.get_debug()
+                );
+                break;
+            }
+            _ => (),
+        }
+    }
+
+    let ret = pipeline.set_state(gst::State::Null);
+    assert_ne!(ret, gst::StateChangeReturn::Failure);
+}