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Using libmpv in Rust

published 07/09/2023 • 3m reading time • 375 views

I recently finish a project I had been wanting to work on for a long time (video-presenter). It allows you to define cuepoints on a video and kinda use it like a slideshow, skipping to different cuepoints and waiting before continuing past one. Anyway, to support a wide selection of video formats, I decided to use libmpv (source).

This article is mostly about compiling and linking with the libmpv library in Rust, but there is a small code example too.

The Code

When I searched for “libmpv rust” I found the mpv crate, but that is deprecated and the README suggested using libmpv-rs, so thats what I picked. Using this crate is fairly easy, here is a simple example to play ‘video.mp4’.

Cargo.toml:

# SNIP #

[dependencies]
libmpv = "2.0.1"

main.rs:

use libmpv::Mpv;

fn main() {
    // Create new MPV context
    let mpv = Mpv::new().unwrap();

    // Play a file
    mpv.playlist_load_files(&[("video.mp4", FileState::AppendPlay, None)]).unwrap();

    // Create an event listener for "playback-time"
    let mut events = self.mpv.create_event_context();
    events
        .observe_property("playback-time", libmpv::Format::Double, 0)
        .unwrap();

    loop {
        // The timeout is completely arbitrary, but I saw 1000 being used in other projects, so
        let event = match events.wait_event(1000.0) {
            Some(e) => e.unwrap(),
            None => continue,
        };

        match event {
            // Handle the playback-time event
            Event::PropertyChange {
                name: "playback-time",
                change: PropertyData::Double(val),
                ..
            } => {
                println!("Time: {val}s");
            }
            _ => {}
        }
    }
}

Compiling

Linux

Now, if you try to compile this, you may get an error like “mpv.lib not found”. If you are on Linux this could be as simple to fix as installing the libmpv package. On Ubuntu, you can use sudo apt install libmpv-dev.

Trying to run the example again now, should open a window and start playback while printing the time to stdout every few frames.

Windows

On Windows, this process is a bit more complicated. First you will need to download the libmpv files (definitions and dll), you can do this from its Sourceforge page. Because the libmpv-rs crate is outdated (requires major version of 1), you will need to make sure you download an older version, like x86_64-20201220-git-dde0189.7z.

Extracting the 7zip archive will revel the following files:

libmpv.dll.a
mpv-1.dll
mpv.def

include/
    client.h
    opengl_cb.h
    render.h
    render_gl.h
    stream_cb.h

You will need to copy the mpv-1.dll and mpv.def files into a folder in your project, I would suggest something like lib. You now need to generate the required .lib file.

Now go into the lib folder with CMD (PowerShell did not work), and run the following commands:

If you are using a different version of Visual Studio, you may need to change this command.

"C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Auxiliary\Build\vcvarsall.bat" x64

It sets up the environment for the specified platform, if you aren’t on x64, pass one of the supported platforms:

• x86
• x86_amd64
• x86_x64
• x86_arm
• x86_arm64
• amd64
• x64
• amd64_x86
• x64_x86
• amd64_arm
• x64_arm
• amd64_arm64
• x64_arm64

Now, before running this command, open mpv.def and make sure the first line is EXPORTS. If it is not, add it.

lib /def:mpv.def /name:mpv-1.dll /out:mpv.lib /MACHINE:X64

This command is part of the Microsoft Library Manager, and we will be using it to generate the mpv.lib file. Just like before, if file names or the platform in the command are not correct, change them. If all goes well, you should see Creating library mpv.lib and object mpv.exp.

Now you just need to let cargo know where to find this lib file. If you have not already, make a build.rs file, then add the following code, being sure to change the path if you chose a name other then lib:

fn main() {
    println!("cargo:rustc-link-search=lib");
}

Running cargo b should now work, but running the compiled application probably wont. To fix that, just copy the mpv-1.dll file from lib into the directory of the executable (target/debug or target/release) or put it in your PATH. Now you should be able to run your application! Just remember to also ship this DLL if you are publishing your program.

Conclusion

Hopefully this was able to help someone. I was easily able to get my video-presenter program to work on Linux, but had a lot of trouble compiling and running it on Windows. I just figured it out today, and decided it might be worth sharing if anyone else is in a similar position.

References

Here are some more resources that may also be helpful:

• libmpv Docs
• Compiling mpv on Windows
• libmpv-rs Github Issue