安全video4linux (v4l)绑定

此包提供对Video for Linux (V4L)堆栈的安全绑定。现代设备驱动程序通常会实现v4l2 API，而较旧的驱动程序可能依赖于传统的v4l API。这些传统设备可以通过选择此包的libv4l功能来使用此包。

目标

此包应提供v4l-sys包，以便能够完全（但不安全）访问libv4l*。在此基础上，将提供一个高级、更符合习惯的API来在Linux中使用视频捕获设备。

将提供简单的实用程序应用程序来列出设备和捕获帧。计划在未来提供一个简单的OpenGL/Vulkan查看器来显示帧。

变更日志

请参阅CHANGELOG.md

依赖关系

您可以选择两种依赖关系（两者都由此包内部提供）

• libv4l-sys

  链接到libv4l*堆栈，包括libv4l1、libv4l2、libv4lconvert。这的优点是可以通过libv4lconvert等在用户空间中模拟常见的捕获格式，如RGB3。然而，一些功能，如用户ptr缓冲区，在libv4l中不受支持。

• v4l2-sys

  仅使用由videodev2.h提供的Linux内核提供的v4l2 API。您将获得所有v4l2功能的支持，如用户ptr缓冲区，但如果您需要例如RGB/BGR缓冲区（可能不被通用设备如网络摄像头支持），则可能需要自行进行格式转换。

通过选择作为此包的功能来启用libv4l或v4l2后端。

用法

以下是一个使用此包的快速示例。它介绍了从流式设备（例如网络摄像头）捕获帧的基本知识。

use v4l::buffer::Type;
use v4l::io::mmap::Stream;
use v4l::io::traits::CaptureStream;
use v4l::video::Capture;
use v4l::Device;
use v4l::FourCC;

fn main() {
    // Create a new capture device with a few extra parameters
    let mut dev = Device::new(0).expect("Failed to open device");

    // Let's say we want to explicitly request another format
    let mut fmt = dev.format().expect("Failed to read format");
    fmt.width = 1280;
    fmt.height = 720;
    fmt.fourcc = FourCC::new(b"YUYV");
    let fmt = dev.set_format(&fmt).expect("Failed to write format");

    // The actual format chosen by the device driver may differ from what we
    // requested! Print it out to get an idea of what is actually used now.
    println!("Format in use:\n{}", fmt);

    // Now we'd like to capture some frames!
    // First, we need to create a stream to read buffers from. We choose a
    // mapped buffer stream, which uses mmap to directly access the device
    // frame buffer. No buffers are copied nor allocated, so this is actually
    // a zero-copy operation.

    // To achieve the best possible performance, you may want to use a
    // UserBufferStream instance, but this is not supported on all devices,
    // so we stick to the mapped case for this example.
    // Please refer to the rustdoc docs for a more detailed explanation about
    // buffer transfers.

    // Create the stream, which will internally 'allocate' (as in map) the
    // number of requested buffers for us.
    let mut stream = Stream::with_buffers(&mut dev, Type::VideoCapture, 4)
        .expect("Failed to create buffer stream");

    // At this point, the stream is ready and all buffers are setup.
    // We can now read frames (represented as buffers) by iterating through
    // the stream. Once an error condition occurs, the iterator will return
    // None.
    loop {
        let (buf, meta) = stream.next().unwrap();
        println!(
            "Buffer size: {}, seq: {}, timestamp: {}",
            buf.len(),
            meta.sequence,
            meta.timestamp
        );

        // To process the captured data, you can pass it somewhere else.
        // If you want to modify the data or extend its lifetime, you have to
        // copy it. This is a best-effort tradeoff solution that allows for
        // zero-copy readers while enforcing a full clone of the data for
        // writers.
    }
}

请查看提供的examples以获取更多示例应用程序。