ff-preview

Real-time video preview and proxy workflow for Rust. Provides frame-accurate seek, audio-master A/V sync, a FrameSink trait for custom renderers, RGBA pixel delivery, and proxy generation with auto-substitution.

ff-preview adds a real-time, A/V-synchronised playback and seek loop on top of the decode primitives, converting frames to RGBA via libswscale for display. Decoding is delegated to ff-decode; this crate owns the playback clock, frame-accurate seek, and a FrameSink trait for custom renderers. Errors are typed and chain their source (PreviewError), so a failure reads as an actionable message rather than a raw FFmpeg return code.

It is an independent crate: use it on its own, or combine it with the other ff-* crates to build any media app or editing model. The ff-* crates are model-free primitives that impose no editing model; avio is one editing engine built on top of them. See the library comparison to choose the right layer.

Installation

[dependencies]
ff-preview = "0.18"

# Enable async support
ff-preview = { version = "0.18", features = ["tokio"] }

# Enable proxy generation
ff-preview = { version = "0.18", features = ["proxy"] }

Quick Start

Playback with a custom RGBA sink

PreviewPlayer::open probes the file and prepares the pipeline. Call split() to obtain an exclusive PlayerRunner (owns the decode pipeline; register the sink and drive it with run()) and a cloneable PlayerHandle (non-blocking play / pause / seek / stop controls).

use std::thread;
use ff_preview::{PreviewPlayer, RgbaSink};

fn main() -> Result<(), ff_preview::PreviewError> {
    let (mut runner, handle) = PreviewPlayer::open("video.mp4")?.split();

    let sink = RgbaSink::new();
    let frames = sink.frame_handle(); // Arc<Mutex<Option<RgbaFrame>>> for the render thread
    runner.set_sink(Box::new(sink));

    thread::spawn(move || {
        let _ = runner.run();
    });

    handle.play();

    // In the render loop (any thread):
    if let Some(frame) = frames.lock().unwrap().as_ref() {
        // upload_to_gpu(&frame.data, frame.width, frame.height);
        let _ = (&frame.data, frame.width, frame.height, frame.pts);
    }

    Ok(())
}

Frame-accurate seek

use std::path::Path;
use std::time::Duration;
use ff_preview::{DecodeBuffer, FrameResult};

fn main() -> Result<(), ff_preview::PreviewError> {
    let mut buf = DecodeBuffer::open(Path::new("video.mp4")).build()?;
    buf.seek(Duration::from_secs(30))?;

    loop {
        match buf.pop_frame() {
            FrameResult::Frame(f) => {
                println!("pts: {:?}", f.timestamp().as_duration());
                break;
            }
            FrameResult::Seeking(_) => std::thread::sleep(Duration::from_millis(5)),
            FrameResult::Eof => break,
        }
    }

    Ok(())
}

Proxy generation

Requires the proxy feature (--features proxy). A file goes in, a lower-resolution proxy file comes out at {output_dir}/{stem}_proxy_{res}.mp4.

use std::path::Path;
use ff_preview::{ProxyGenerator, ProxyResolution};

fn main() -> Result<(), ff_preview::PreviewError> {
    let proxy_path = ProxyGenerator::new(Path::new("original_1080p.mp4"))?
        .resolution(ProxyResolution::Quarter)
        .output_dir(&std::env::temp_dir())
        .generate()?;

    println!("proxy at {}", proxy_path.display());
    Ok(())
}

Feature Flags

Error Handling

Common variants (not exhaustive):

PreviewError implements ff_format::MediaError, so err.is_recoverable() / err.is_fatal() work uniformly with the other ff-* crates.

MSRV

Rust 1.93.0 (edition 2024).

License

MIT OR Apache-2.0