gstreamer-rs/examples/src/bin/playbin.rs

// This example demonstrates GStreamer's playbin element.
// This element takes an arbitrary URI as parameter, and if there is a source
// element within gstreamer, that supports this uri, the playbin will try
// to automatically create a pipeline that properly plays this media source.
// For this, the playbin internally relies on more bin elements, like the
// autovideosink and the decodebin.
// Essentially, this element is a single-element pipeline able to play
// any format from any uri-addressable source that gstreamer supports.
// Much of the playbin's behavior can be controlled by so-called flags, as well
// as the playbin's properties and signals.

use std::env;

use gst::prelude::*;

#[path = "../examples-common.rs"]
mod examples_common;

fn example_main() {
    gst::init().unwrap();

    let args: Vec<_> = env::args().collect();
    let uri: &str = if args.len() == 2 {
        args[1].as_ref()
    } else {
        println!("Usage: playbin uri");
        std::process::exit(-1)
    };

    // Create a new playbin element, and tell it what uri to play back.
    let playbin = gst::ElementFactory::make("playbin")
        .property("uri", uri)
        .build()
        .unwrap();

    // For flags handling
    // With flags, one can configure playbin's behavior such as whether it
    // should play back contained video streams, or if it should render subtitles.
    // let flags = playbin.get_property("flags").unwrap();
    // let flags_class = FlagsClass::new(flags.type_()).unwrap();
    // let flags = flags_class.builder_with_value(flags).unwrap()
    //     .unset_by_nick("text")
    //     .unset_by_nick("video")
    //     .build()
    //     .unwrap();
    // playbin.set_property_from_value("flags", &flags).unwrap();

    // The playbin also provides any kind of metadata that it found in the played stream.
    // For this, the playbin provides signals notifying about changes in the metadata.
    // Doing this with a signal makes sense for multiple reasons.
    // - The metadata is only found after the pipeline has been started
    // - Live streams (such as internet radios) update this metadata during the stream
    // Note that this signal will be emitted from the streaming threads usually,
    // not the application's threads!
    playbin.connect("audio-tags-changed", false, |values| {
        // The metadata of any of the contained audio streams changed
        // In the case of a live-stream from an internet radio, this could for example
        // mark the beginning of a new track, or a new DJ.
        let playbin = values[0]
            .get::<glib::Object>()
            .expect("playbin \"audio-tags-changed\" signal values[1]");
        // This gets the index of the stream that changed. This is neccessary, since
        // there could e.g. be multiple audio streams (english, spanish, ...).
        let idx = values[1]
            .get::<i32>()
            .expect("playbin \"audio-tags-changed\" signal values[1]");

        println!("audio tags of audio stream {idx} changed:");

        // HELP: is this correct?
        // We were only notified about the change of metadata. If we want to do
        // something with it, we first need to actually query the metadata from the playbin.
        // We do this by facilliating the get-audio-tags action-signal on playbin.
        // Sending an action-signal to an element essentially is a function call on the element.
        // It is done that way, because elements do not have their own function API, they are
        // relying on GStreamer and GLib's API. The only way an element can communicate with an
        // application is via properties, signals or action signals (or custom messages, events, queries).
        // So what the following code does, is essentially asking playbin to tell us its already
        // internally stored tag list for this stream index.
        let tags = playbin.emit_by_name::<Option<gst::TagList>>("get-audio-tags", &[&idx]);

        if let Some(tags) = tags {
            if let Some(artist) = tags.get::<gst::tags::Artist>() {
                println!("  Artist: {}", artist.get());
            }

            if let Some(title) = tags.get::<gst::tags::Title>() {
                println!("  Title: {}", title.get());
            }

            if let Some(album) = tags.get::<gst::tags::Album>() {
                println!("  Album: {}", album.get());
            }
        }

        None
    });

    // The playbin element itself is a playbin, so it can be used as one, despite being
    // created from an element factory.
    let bus = playbin.bus().unwrap();

    playbin
        .set_state(gst::State::Playing)
        .expect("Unable to set the pipeline to the `Playing` state");

    for msg in bus.iter_timed(gst::ClockTime::NONE) {
        use gst::MessageView;

        match msg.view() {
            MessageView::Eos(..) => break,
            MessageView::Error(err) => {
                println!(
                    "Error from {:?}: {} ({:?})",
                    err.src().map(|s| s.path_string()),
                    err.error(),
                    err.debug()
                );
                break;
            }
            MessageView::StateChanged(state_changed) =>
            // We are only interested in state-changed messages from playbin
            {
                if state_changed.src().map(|s| s == &playbin).unwrap_or(false)
                    && state_changed.current() == gst::State::Playing
                {
                    // Generate a dot graph of the pipeline to GST_DEBUG_DUMP_DOT_DIR if defined
                    let bin_ref = playbin.downcast_ref::<gst::Bin>().unwrap();
                    bin_ref.debug_to_dot_file(gst::DebugGraphDetails::all(), "PLAYING");
                }
            }

            _ => (),
        }
    }

    playbin
        .set_state(gst::State::Null)
        .expect("Unable to set the pipeline to the `Null` state");
}

fn main() {
    // tutorials_common::run is only required to set up the application environment on macOS
    // (but not necessary in normal Cocoa applications where this is set up automatically)
    examples_common::run(example_main);
}