YUV数据格式在这儿已经说得很好了：[https://www.jianshu.com/p/3e44c2262775](https://www.jianshu.com/p/3e44c2262775)
1、获取camera的最佳预览尺寸
(1)、如果已经设置好了，通过以下方法直接获取
````
val size = mCamera.parameters.previewSize
````
(2)、最佳尺寸获取方法可以参考以下函数
````
fun findCameraBestPreviewSize(context: Context, camera: Camera?): Point? {
if(camera == null) {
return null
}
val manager = context.getSystemService(Context.WINDOW_SERVICE) as WindowManager
val display = manager.defaultDisplay
val point = Point()
try {
display.getSize(point)
} catch (ignore: NoSuchMethodError) {
point.x = display.width
point.y = display.height
}
val orientation = context.resources.configuration.orientation
var width = 0
var height = 0
if (orientation == Configuration.ORIENTATION_PORTRAIT) {
//竖屏情况
width = point.y
height = point.x
} else {
//横屏情况
width = point.x
height = point.y
}
val previewSizes = camera.parameters.supportedPreviewSizes
for (size in previewSizes) {
if (size.width == width && size.height == height) {
return Point(width, height)
}
}
val reqRatio = width.toFloat() / height
//找到 摄像头预览比例 和 屏幕比例最接近的 预览尺寸
var min = java.lang.Float.MAX_VALUE
var retSize: Camera.Size? = null
for (size in previewSizes) {
val deltaRatio = abs(reqRatio - size.width.toFloat() / size.height)
if (deltaRatio < min) {
min = deltaRatio
retSize = size
}
}
return if (retSize == null) null else Point(retSize.width, retSize.height)
}
````
2、camera的预览尺寸表示实际的YUV数据内，Y数据的数量
此处camera返回数据为NV21数据，【具体格式问题请参考上述YUV数据格式解析的博客链接】，与下图格式（NV12）类似，不过NV21V在前U在后：
````
// data：预览返回的字节数组，width：camera预览尺寸宽度， height：camera预览尺寸高度
private fun rotateYuv420SP(data: ByteArray?, width: Int, height: Int): ByteArray? {
if (data == null) {
return null
}
//YUV420sp（nv21格式：V 前 U 后）Y和UV的数量比为：2：1
if (data.size != width * height * 3 / 2) {
return null
}
//竖屏下需要旋转
var k = 0
val rotatedData = ByteArray(data.size)
//翻转 Y
for (j in 0 until width) {
for (i in (height - 1) downTo 0) {
rotatedData[k++] = data[i * width + j]
}
}
val uvWidth = width
val uvHeight = height / 2
//翻转 UV
for (j in 0 until uvWidth step 2) {
for (i in (uvHeight + height - 1) downTo (height)) {
rotatedData[k++] = data[i * uvWidth + j]
rotatedData[k++] = data[i * uvWidth + j + 1]
}
}
return rotatedData
}
````
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