如何使用选定屏幕区域的recordRTC节点模块录制桌面屏幕视频？

Question

我正在使用 NW.js 开发桌面应用程序，其中需要记录桌面屏幕的选定区域。目前使用 RecordRTC 节点模块录制视频。但这给了我全屏视频录制。如果有任何其他软件包可以跨平台（win/linux/mac）实现这一点，请提供帮助。

Answer 1

请查看此演示（名称为“使用 RecordRTC 记录裁剪屏幕”）：

• https://www.webrtc-experiment.com/RecordRTC/simple-demos/record-cropped-screen.html

这是完整的 HTML 代码（在任何 HTTPs 页面或 localhost 或 node-webkit 上尝试）：

<button id="btn-start-recording">Start Recording</button>
<button id="btn-stop-recording" style="display: none;">Stop Recording</button>

<br><hr>

<div id="edit-panel" style="border-bottom: 1px solid;">
    <div>
        <label for="x">X</label>
        <input type="number" name="x" id="x" value="0" />
    </div>
    <div>
        <label for="y">Y</label>
        <input type="number" name="y" id="y" value="0" />
    </div>
    <div>
        <label for="w">Width (-1 = Full size)</label>
        <input type="number" name="w" id="w" value="-1" />
    </div>
    <div>
        <label for="h">Height (-1 = Full size)</label>
        <input type="number" name="h" id="h" value="-1" />
    </div>

    <button id="update" style="display: none;">Update X-Y Width-Height Coordinates</button>

    <canvas></canvas>
</div>

<video id="mediaElement"></video>

<script src="https://cdn.webrtc-experiment.com/RecordRTC.js"></script>
<script src="https://cdn.WebRTC-Experiment.com/getScreenId.js"></script>
<script>
// this script tag is taken from: https://github.com/andersevenrud/webrtc-screenshare-crop-demo
var CROP_X = 10;
var CROP_Y = 20;
var CROP_W = 320; // default width
var CROP_H = 240; // default height
var VIDEO_WIDTH = 0;
var VIDEO_HEIGHT = 0;
var MAX_VIDEO_WIDTH = 1920;
var MAX_VIDEO_HEIGHT = 1080;
var _canvas;
var _context;

var htmlCanvasElement = document.querySelector('canvas');

// Form elements
document.getElementById("x").value = CROP_X;
document.getElementById("y").value = CROP_Y;
document.getElementById("w").value = CROP_W;
document.getElementById("h").value = CROP_H;

document.getElementById("update").onclick = function() {
    var x = document.getElementById("x").value << 0;
    var y = document.getElementById("y").value << 0;
    var w = document.getElementById("w").value << 0;
    var h = document.getElementById("h").value << 0;

    if (x >= 0) {
        CROP_X = x;
    }
    if (y >= 0) {
        CROP_Y = y;
    }

    CROP_W = w || 0;
    CROP_H = h || 0;
};

_context = htmlCanvasElement.getContext('2d');

/**
 * Crops a video frame and shows it to the user
 */
function CropFrame(ev, stream, video, callback) {
    callback = callback || function() {};

    _canvas = htmlCanvasElement;

    if (CROP_X < 0) {
        CROP_X = 0;
    }
    if (CROP_Y < 0) {
        CROP_Y = 0;
    }
    if (CROP_W <= 0) {
        CROP_W = VIDEO_WIDTH;
    }
    if (CROP_H <= 0) {
        CROP_H = VIDEO_HEIGHT;
    }
    if (CROP_W > MAX_VIDEO_WIDTH) {
        CROP_W = MAX_VIDEO_WIDTH;
    }
    if (CROP_H > MAX_VIDEO_HEIGHT) {
        CROP_W = MAX_VIDEO_HEIGHT;
    }

    _canvas.width = CROP_W;
    _canvas.height = CROP_H;

    _context.drawImage(video, CROP_X, CROP_Y, CROP_W, CROP_H, 0, 0, CROP_W, CROP_H);

    // We need to scale down the image or else we get HTTP 414 Errors
    // Also we scale down because of RTC message length restriction
    var scanvas = document.createElement('canvas');
    scanvas.width = _canvas.width;
    scanvas.height = _canvas.height;

    var wRatio = _canvas.width / 320;
    var hRatio = _canvas.height / 240;
    var maxRatio = Math.max(wRatio, hRatio);
    if (maxRatio > 1) {
        scanvas.width = _canvas.width / maxRatio;
        scanvas.height = _canvas.height / maxRatio;
    }
    scanvas.getContext('2d').drawImage(_canvas, 0, 0, scanvas.width, scanvas.height);

    callback(scanvas.toDataURL("image/jpeg"));
}

var recorder;

function captureScreen(cb) {
    getScreenId(function(error, sourceId, screen_constraints) {
        navigator.getUserMedia(screen_constraints, cb, function(error) {
            console.error('getScreenId error', error);

            alert('Failed to capture your screen. Please check Chrome console logs for further information.');
        });
    });
}

var mediaElement = document.querySelector('#mediaElement');

document.querySelector('#btn-start-recording').onclick = function() {
    document.querySelector('#btn-start-recording').style.display = 'none';

    navigator.getUserMedia = navigator.getUserMedia || navigator.mozGetUserMedia || navigator.webkitGetUserMedia;
    captureScreen(function(screen) {
        var inited = false;

        mediaElement.ontimeupdate = function(ev) {
            if (!inited) {
                VIDEO_WIDTH = mediaElement.offsetWidth;
                VIDEO_HEIGHT = mediaElement.offsetHeight;

                mediaElement.style.display = 'none';
                document.querySelector('#edit-panel').style.display = 'block';

                inited = true;
            }

            CropFrame(ev, screen, mediaElement);
        };

        mediaElement.src = URL.createObjectURL(screen);
        mediaElement.play();
        mediaElement.screen = screen;

        addStreamStopListener(screen, function() {
            document.querySelector('#btn-stop-recording').onclick();
        });

        // RecordRTC goes here
        var captureStream = htmlCanvasElement.captureStream();
        recorder = RecordRTC(captureStream, {
            type: 'video'
        });
        recorder.startRecording();

        document.querySelector('#btn-stop-recording').style.display = 'inline';
    });
};

document.querySelector('#btn-stop-recording').onclick = function() {
    document.querySelector('#btn-stop-recording').style.display = 'none';

    recorder.stopRecording(function() {
        var blob = recorder.getBlob();

        document.querySelector('#edit-panel').style.display = 'none';
        mediaElement.style.display = 'block';

        mediaElement.src = URL.createObjectURL(blob);
        mediaElement.play();

        if (mediaElement.screen && mediaElement.screen.getVideoTracks) {
            mediaElement.screen.stop();
            mediaElement.screen = null;
        }

        document.querySelector('#btn-start-recording').style.display = 'inline';
    });
};

function addStreamStopListener(stream, callback) {
    var streamEndedEvent = 'ended';
    if ('oninactive' in stream) {
        streamEndedEvent = 'inactive';
    }
    stream.addEventListener(streamEndedEvent, function() {
        callback();
        callback = function() {};
    }, false);
    stream.getAudioTracks().forEach(function(track) {
        track.addEventListener(streamEndedEvent, function() {
            callback();
            callback = function() {};
        }, false);
    });
    stream.getVideoTracks().forEach(function(track) {
        track.addEventListener(streamEndedEvent, function() {
            callback();
            callback = function() {};
        }, false);
    });
}

function querySelectorAll(selector) {
    return Array.prototype.slice.call(document.querySelectorAll(selector));
}

querySelectorAll('input').forEach(function(input) {
    input.onkeyup = input.oninput = function() {
        if (!document.querySelector('#update').onclick) return;
        document.querySelector('#update').onclick();
    };
});
</script>