Cargo.toml

[package]
name = "gst-test"
version = "0.1.0"
authors = ["Joe Neeman <joeneeman@gmail.com>"]
edition = "2018"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
gstreamer = "0.15.4"
anyhow = "1.0.27"
thiserror = "1.0.14"
gstreamer-audio = "0.15.3"
console = { version = "0.12.0", default-features = false }

main.rs

use anyhow::Error;
use gst::prelude::*;
use gst::{ClockTime, Element, ElementFactory, Pipeline, SeekFlags, SeekType, State};
use gstreamer as gst;

#[derive(Debug, thiserror::Error)]
#[error("Missing element {0}")]
struct MissingElement(&'static str);

fn create_pipeline() -> Result<Pipeline, Error> {
    gst::init()?;

    let pipeline = Pipeline::new(None);
    let src = ElementFactory::make("audiotestsrc", None).map_err(|_| MissingElement("testsrc"))?;
    let scale = ElementFactory::make("scaletempo", Some("scale"))
        .map_err(|_| MissingElement("scaletempo"))?;
    let sink = ElementFactory::make("autoaudiosink", Some("sink"))
        .map_err(|_| MissingElement("autoaudiosink"))?;

    pipeline.add_many(&[&src, &scale, &sink])?;
    Element::link_many(&[&src, &scale, &sink])?;

    Ok(pipeline)
}

fn main_loop(pipeline: Pipeline) -> Result<(), Error> {
    pipeline.set_state(State::Playing)?;
    let mut velocity = 1.0;

    let term = console::Term::stdout();
    let sink = pipeline.get_by_name("sink").unwrap();
    use console::Key;
    while let Ok(b) = term.read_key() {
        let mut new_vel = velocity;
        match b {
            Key::ArrowRight => new_vel += 2.0,
            Key::ArrowLeft => new_vel -= 2.0,
            _ => {}
        }

        if new_vel != velocity {
            let pos = dbg!(pipeline.query_position::<ClockTime>()).unwrap();
            velocity = dbg!(new_vel);
            if velocity > 0.0 {
                sink.seek(
                    velocity,
                    SeekFlags::FLUSH | SeekFlags::ACCURATE,
                    SeekType::Set,
                    pos,
                    SeekType::Set,
                    ClockTime::none(),
                )
                .unwrap();
            } else {
                sink.seek(
                    velocity,
                    SeekFlags::FLUSH | SeekFlags::ACCURATE,
                    SeekType::Set,
                    ClockTime::from_nseconds(0),
                    SeekType::Set,
                    pos,
                )
                .unwrap();
            }
        }
    }

    pipeline.set_state(State::Null)?;

    Ok(())
}

fn main() {
    match create_pipeline().and_then(main_loop) {
        Ok(r) => r,
        Err(e) => eprintln!("Error! {}", e),
    }
}