Add basic-tutorial-4 from the GStreamer tutorials

https://cgit.freedesktop.org/gstreamer/gst-docs/tree/examples/tutorials/basic-tutorial-4.c

Fixes https://github.com/sdroege/gstreamer-rs/pull/39

tutorials/src/bin/basic-tutorial-4.rs

@@ -0,0 +1,149 @@
+extern crate gstreamer as gst;
+use std::io;
+use std::io::Write;
+use gst::prelude::*;
+use gst::MessageView;
+
+struct CustomData {
+    playbin: gst::Element,    // Our one and only element
+    playing: bool,            // Are we in the PLAYING state?
+    terminate: bool,          // Should we terminate execution?
+    seek_enabled: bool,       // Is seeking enabled for this media?
+    seek_done: bool,          // Have we performed the seek already?
+    duration: gst::ClockTime, // How long does this media last, in nanoseconds
+}
+
+fn main() {
+    // Initialize GStreamer
+    gst::init().unwrap();
+
+    // Creat the playbin element
+    let playbin =
+        gst::ElementFactory::make("playbin", "playbin").expect("Failed to create playbin element");
+
+    // Set the URI to play
+    let uri = "https://www.freedesktop.org/software/gstreamer-sdk/data/media/sintel_trailer-480p.webm";
+    playbin
+        .set_property("uri", &uri)
+        .expect("Can't set uri property on playbin");
+
+    // Start playing
+    let ret = playbin.set_state(gst::State::Playing);
+    assert_ne!(ret, gst::StateChangeReturn::Failure);
+
+    // Listen to the bus
+    let bus = playbin.get_bus().unwrap();
+    let mut custom_data = CustomData {
+        playbin: playbin,
+        playing: false,
+        terminate: false,
+        seek_enabled: false,
+        seek_done: false,
+        duration: gst::CLOCK_TIME_NONE,
+    };
+
+    while !custom_data.terminate {
+        let msg = bus.timed_pop(100 * gst::MSECOND);
+
+        match msg {
+            Some(msg) => {
+                handle_message(&mut custom_data, &msg);
+            }
+            None => {
+                if custom_data.playing {
+                    let position = custom_data
+                        .playbin
+                        .query_position(gst::Format::Time)
+                        .expect("Could not query current position.");
+                    let position = position as gst::ClockTime;
+
+                    // If we didn't know it yet, query the stream duration
+                    if custom_data.duration == gst::CLOCK_TIME_NONE {
+                        custom_data.duration = custom_data
+                            .playbin
+                            .query_duration(gst::Format::Time)
+                            .expect("Could not query current duration.") as
+                            gst::ClockTime;
+                    }
+
+                    // Print current position and total duration
+                    print!("\rPosition {} / {}", position, custom_data.duration);
+                    io::stdout().flush().unwrap();
+
+                    if custom_data.seek_enabled && !custom_data.seek_done &&
+                        position > 10 * gst::SECOND
+                    {
+                        println!("\nReached 10s, performing seek...");
+                        custom_data
+                            .playbin
+                            .seek_simple(
+                                gst::Format::Time,
+                                gst::SeekFlags::FLUSH | gst::SeekFlags::KEY_UNIT,
+                                (30 * gst::SECOND) as i64,
+                            )
+                            .expect("Failed to seek.");
+                        custom_data.seek_done = true;
+                    }
+                }
+            }
+        }
+    }
+
+    // Shutdown pipeline
+    let ret = custom_data.playbin.set_state(gst::State::Null);
+    assert_ne!(ret, gst::StateChangeReturn::Failure);
+}
+
+fn handle_message(custom_data: &mut CustomData, msg: &gst::GstRc<gst::MessageRef>) {
+    match msg.view() {
+        MessageView::Error(err) => {
+            println!(
+                "Error received from element {}: {} ({:?})",
+                msg.get_src().get_path_string(),
+                err.get_error(),
+                err.get_debug()
+            );
+            custom_data.terminate = true;
+        }
+        MessageView::Eos(..) => {
+            println!("End-Of-Stream reached.");
+            custom_data.terminate = true;
+        }
+        MessageView::DurationChanged(_) => {
+            // The duration has changed, mark the current one as invalid
+            custom_data.duration = gst::CLOCK_TIME_NONE;
+        }
+        MessageView::StateChanged(state) => if msg.get_src() == custom_data.playbin {
+            let new_state = state.get_current();
+            let old_state = state.get_old();
+
+            println!(
+                "Pipeline state changed from {:?} to {:?}",
+                old_state,
+                new_state
+            );
+
+            custom_data.playing = new_state == gst::State::Playing;
+            if custom_data.playing {
+                let query = gst::Query::new_seeking(gst::Format::Time);
+                if custom_data.playbin.query(query.get_mut().unwrap()) {
+                    match query.view() {
+                        gst::QueryView::Seeking(seek) => {
+                            let (_fmt, seekable, start, end) = seek.get();
+                            custom_data.seek_enabled = seekable;
+                            if seekable {
+                                println!("Seeking is ENABLED from {} to {}", start, end)
+                            } else {
+                                println!("Seeking is DISABLED for this stream.")
+                            }
+                        }
+                        _ => unreachable!(),
+                    }
+                } else {
+                    eprintln!("Seeking query failed.")
+                }
+            }
+        },
+        _ => (),
+    }
+}