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我正在开发一个将 JPEG 图像流（MJPEG 流）发送到远程 PC 的应用程序。我无法更改相机参数中的预览帧速率。似乎无论我设置什么速率，相机都只能以 15 fps 的速度给我一帧。起初我以为是图像压缩，然后传输数据。但是我创建了一个调试实例，我在其中存储了第一个压缩的 JPEG 图像，并在每次调用 onPreviewFrame 函数时发送该图像。这会产生可靠的 15fps，但我将其设置为 30fps。任何人都知道为什么fps如此不一致？当我将它设置为压缩每个预览帧并通过 wifi 发送时，我得到了 5-40 FPS 的速率，并且它在整个地方跳跃。

这是我的预览代码（全屏设置相机）

public class Preview extends SurfaceView implements PreviewCallback, SurfaceHolder.Callback {
SurfaceHolder mHolder;
Camera mCamera;
DatagramSocket udpSocket = null;
final int PORT = 1235;
final String IPAddress = "192.168.1.101";
int packetSize = 1024; // Specify max size of each UDP packet
int WIDTH = 640;
int HEIGHT = 480;   
int FPS = 30;       
int quality = 70;
/**
 * Initialize the Camera Preview Holder and create a udpSocket.
 * @param context
 */
Preview(Context context) {
    super(context);
    mHolder = getHolder();
    mHolder.addCallback(this);
    mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
    try {
        udpSocket = new DatagramSocket();
    } catch (SocketException e) {
        Log.e(tag, "Error creating UDP Socket!");
    }
}
public void surfaceCreated(SurfaceHolder holder) {
    mCamera = Camera.open();
    try {
       mCamera.setPreviewDisplay(holder);
    } catch (IOException exception) {
        mCamera.release();
        mCamera = null;
        Log.e(tag, "Error settign Camera Preview Holder!");
    }
}
public void surfaceDestroyed(SurfaceHolder holder) {
    mCamera.setPreviewCallback(null);
    mCamera.stopPreview();
    udpSocket.close();
    mCamera.release();
    udpSocket = null;
    mCamera = null;
}
public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
    Camera.Parameters parameters = mCamera.getParameters();
    parameters.setPreviewSize(WIDTH, HEIGHT);
    parameters.setPreviewFrameRate(FPS);
    parameters.setRotation(90);

    mCamera.setParameters(parameters);
    mCamera.setPreviewCallback(this);
    mCamera.startPreview();
}
/** Compresses the preview framer (data) into a JPEG image and send to a host at
 * the specified IPAddress and Port number for playback. Only sends frame if sendFrame
 * is true.
 * (non-Javadoc)
 * @see android.hardware.Camera.PreviewCallback#onPreviewFrame(byte[], android.hardware.Camera)
 * @see android.hardware.Camera
 */
public void onPreviewFrame(byte[] data, Camera camera) {
    final YuvImage imgPreview = new YuvImage(data, ImageFormat.NV21, WIDTH, HEIGHT, null);
    byte[] buffer;
    ByteArrayOutputStream jpegOutStream = new ByteArrayOutputStream();

    int offset = 0;
    int TotalLength, lengthLeft;
    DatagramPacket dgpout;
    // Compress image into JPEG
    imgPreview.compressToJpeg(new Rect(0, 0, imgPreview.getWidth(), imgPreview.getHeight()), quality, jpegOutStream);
    buffer = jpegOutStream.toByteArray();
    TotalLength = lengthLeft = buffer.length;
    // Send frame out. Split into packets of desired length.
    try {
        while(lengthLeft>packetSize){
            dgpout= new DatagramPacket(buffer, offset, packetSize);
            offset+=packetSize;
            lengthLeft-=packetSize;
            dgpout.setAddress(InetAddress.getByName(IPAddress));
            dgpout.setPort(PORT);
            udpSocket.send(dgpout);
        }
        if(lengthLeft>0){
            dgpout= new DatagramPacket(buffer,offset,lengthLeft);
            offset+=lengthLeft;
            lengthLeft-=lengthLeft;
            dgpout.setAddress(InetAddress.getByName(IPAddress));
            dgpout.setPort(PORT);
            udpSocket.send(dgpout);
        }
        Log.i(tag, "Sent Successfully: frame size="+TotalLength +"Buffer Size: "+udpSocket.getSendBufferSize());
    } catch (UnknownHostException e1) {
        Log.e(tag   , "UnknownHostException. Sending failed.");
    } catch (IOException e) {
        Log.e(tag   , "IOException. Sending failed.");
    }
}

}

这是我的调试示例，仅用于一遍又一遍地发送相同的 JPEG

if(sendFrame){
        sendFrame = false;
        final YuvImage imgPreview = new YuvImage(data, ImageFormat.NV21, WIDTH, HEIGHT, null);

        fixImage = data;
                byte[] buffer;
                ByteArrayOutputStream jpegOutStream = new ByteArrayOutputStream();

                int offset = 0;
                int TotalLength, lengthLeft;
                DatagramPacket dgpout;
                // Compress image into JPEG
                imgPreview.compressToJpeg(new Rect(0, 0, imgPreview.getWidth(), imgPreview.getHeight()), quality, jpegOutStream);
                buffer = jpegOutStream.toByteArray();

                fixJPEG = buffer;
                fixTotalLength = buffer.length;

    }
    int lengthLeft = 0;
    int offset = 0;
    DatagramPacket dgpout;
    if(fixImage==null || fixJPEG==null)
        return;
    /* Compress Optional */
    if(true){
        final YuvImage imgPreview = new YuvImage(fixImage, ImageFormat.NV21, WIDTH, HEIGHT, null);
        ByteArrayOutputStream jpegOutStream = new ByteArrayOutputStream();
        imgPreview.compressToJpeg(new Rect(0, 0, imgPreview.getWidth(), imgPreview.getHeight()), quality, jpegOutStream);
        fixJPEG = jpegOutStream.toByteArray();
    }
    fixTotalLength = lengthLeft = fixJPEG.length;
    // Send frame out. Split into packets of desired length.
    try {
        while(lengthLeft>packetSize){
            dgpout= new DatagramPacket(fixJPEG, offset, packetSize);
            offset+=packetSize;
            lengthLeft-=packetSize;
            dgpout.setAddress(InetAddress.getByName(IPAddress));
            dgpout.setPort(PORT);
            udpSocket.send(dgpout);
        }
        if(lengthLeft>0){
        dgpout= new DatagramPacket(fixJPEG,offset,lengthLeft);
            offset+=lengthLeft;
            lengthLeft-=lengthLeft;
            dgpout.setAddress(InetAddress.getByName(IPAddress));
            dgpout.setPort(PORT);
            udpSocket.send(dgpout);
        }
        Log.i(tag, "Sent Successfully: frame size="+fixTotalLength +"Buffer Size: "+udpSocket.getSendBufferSize());
    } catch (UnknownHostException e1) {
        Log.e(tag   , "UnknownHostException. Sending failed.");
    } catch (IOException e) {
        Log.e(tag   , "IOException. Sending failed.");
    }

有没有人有任何提高效率的想法？这是否发生在所有设备上？我正在运行 Android 2.2。任何想法表示赞赏。

*编辑添加了整个预览类

4

1 回答 1

2

Atrix 很可能（合法地）无视您更改预览帧速率的请求。

在您的surfaceChanged回调中，尝试调用以下内容并检查调试器中的值：

List<Integer> rates = parameters.getSupportedPreviewFrameRates();

Android 文档说：

返回支持的预览帧速率列表。如果不支持预览帧速率设置，则为 null。

此外，文件setPreviewFrameRate()说：

这是目标帧速率。实际帧速率取决于驱动程序。

因此，Atrix 可能不支持 15 fps 以外的任何预览。

无论如何，使用预览帧率的正确方法是首先调用getSupportedPreviewFrameRates(). 如果它返回非空结果，请在列表中找到与您想要的最接近的数字并将其传递给setPreviewFrameRate(). 否则，您将不得不接受设备支持的任何速率。

于 2011-07-15T22:08:24.343 回答