如何在Firefox中实现基于视频约束的getusermedia捕获?在Chrome中，一切都是按照代码进行的，但在Fi

Question

当我想从getusermedia捕获图像时，我遇到了一个问题，Firefox中捕获的图像没有保留我在视频约束中设置的比率。这是获得视频的比率，但从我所看到的视频来看，它没有受到Firefox 中的限制

if(navigator.mediaDevices && navigator.mediaDevices.getUserMedia) {
if(window.innerWidth >= 600){
this.canvasWidth = 480;
this.canvasHeight = 360;
} else {
this.canvasWidth = 240;
this.canvasHeight = 240;
}
navigator.mediaDevices.getUserMedia({ audio: false,video: {facingMode: 'user', width: this.canvasWidth * 2, height: this.canvasHeight * 2} }).then(stream => {
this.useWebcam = true;
this.canvas.nativeElement.style.display = 'none';
this.video.nativeElement.srcObject = stream;
this.stream = stream;
this.ref.detectChanges();
this.video.nativeElement.play();
console.log(stream);
}).catch(reason => {
this.useWebcam = false;
if(this.acceptable){
this.acceptable = false;
this.eMessage = reason + "<br/>Please check your camera to continue.";
this.ref.detectChanges();
}
// alert(reason + " nPlease check your camera to continue.")
});
} else {
this.eMessage = "Please check your camera to continue.";
}

这是用来拍照和重新拍照的

capture() {
this.canvas.nativeElement.style.display = 'block';
this.canvas.nativeElement.getContext("2d").scale(-1,1);
this.canvas.nativeElement.getContext("2d").drawImage(this.video.nativeElement, 0, 0, this.canvas.nativeElement.width * 2, this.canvas.nativeElement.height * 2, 0, 0, -1 * this.canvas.nativeElement.width, this.canvas.nativeElement.height);
this.canvas.nativeElement.getContext("2d").restore();
this.captured = this.canvas.nativeElement.toDataURL("image/png");
this.video.nativeElement.style.display = 'none';
}
retake() {
setTimeout(() => {
this.canvas.nativeElement.getContext("2d").scale(-1,1);
this.canvas.nativeElement.getContext("2d").clearRect(0, 0, -1 * this.canvas.nativeElement.width, this.canvas.nativeElement.height);
this.canvas.nativeElement.getContext("2d").restore();
this.canvas.nativeElement.style.display = 'none';
this.video.nativeElement.style.display = 'block';
this.captured = null;
}, 20);
}

如何使用给定的约束制作视频？这段代码在Chrome中有效，在Firefox中无效？谢谢

注：在提问之前，我已经阅读了其他问题，但仍然没有答案。谢谢

Answer 1

向getUserMedia((提供的约束是请求。你不会总是得到你要求的确切尺寸。

我同意你的看法，即谷歌Chrome比Firefox更符合你要求的尺寸。我试图使用exact属性强制Firefox使用精确的维度，但它拒绝了，并出现了违反约束的错误。

我不得不剪辑拍摄的Firefox图像，使其与我在Chrome中拍摄的图像大小相同。为了让拍摄的用户看到这一点，我还安排了一些CSS来剪辑预览窗口。

Answer 2

最后，在试用了我的代码后，我可以预览

positioningVideo(){
//Check Orientation
if(this.videoWidth > this.videoHeight){
let temp = this.videoWidth;
this.videoWidth = this.videoHeight;
this.videoHeight = temp;
}
if(this.videoWidth > (this.canvasWidth * 2)){
this.video.nativeElement.style.maxHeight = '' + this.canvasHeight + 'px' ;
this.video.nativeElement.style.maxWidth = '' + (this.videoWidth / 2) + 'px';
} else if(this.videoHeight > (this.canvasHeight * 2)){
this.video.nativeElement.style.maxWidth = '' + this.canvasWidth + 'px' ;
this.video.nativeElement.style.maxHeight = '' + (this.videoHeight / 2) + 'px';
} else if(this.videoWidth == (this.canvasWidth * 2) && this.videoHeight == (this.canvasHeight * 2)){
this.video.nativeElement.style.maxHeight = '' + this.canvasHeight + 'px' ;
this.video.nativeElement.style.maxWidth = '' + this.canvasWidth + 'px' ;
}
}

我用一些计算来设置我的起始坐标

注意：我使用裁剪中心，所以我计算顶部或左侧的边距。

capture() {
let coorX = 0, coorY = 0;

if(this.videoWidth != (this.canvasWidth * 2)){
coorX = (this.videoWidth - (this.canvasWidth * 2)) / 2;
}
if(this.videoHeight != (this.canvasHeight * 2)){
coorY = (this.videoHeight - (this.canvasHeight * 2)) / 2;
}
this.canvas.nativeElement.style.display = 'block';
this.canvas.nativeElement.getContext("2d").scale(-1,1);
this.canvas.nativeElement.getContext("2d").drawImage(this.video.nativeElement, coorX, coorY, this.canvasWidth * 2, this.canvasHeight * 2, 0, 0, -1 * this.canvasWidth, this.canvasHeight);
this.canvas.nativeElement.getContext("2d").restore();
this.captured = this.canvas.nativeElement.toDataURL("image/png");
this.video.nativeElement.parentElement.style.display = 'none';
}