7

Environment:

Nexus 7 Jelly Bean 4.1.2

Problem:

I'm trying to make a Motion Detection application that works with RTSP using VideoView.

I wish that there was something like an onNewFrameListener

videoView.onNewFrame(Frame frame)

I've tried to get access to the raw frames of an RTSP stream via VideoView but couldn't find any support for that in the Android SDK.

I found out that VideoView encapsulates the Android's MediaPlayer class.

So i dived into the media_jni lib to try and find a way to access the raw frames, But couldn't find the byte buffer or whatever that represents a frame.

Question:

Anyone has an idea where or how can i find this buffer and get access to it ?

Or any other idea of implementing a Motion Detection over a VideoView ?

Even if it's sais that i need to recompile the AOSP.

Danpe
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2 Answers2

3

You can extend the VideoView and override its draw(Canvas canvas) method.

  • Set your bitmap to the canvas received through draw.
  • Call super.draw() which will get the frame drawn onto your bitmap.

  • Access the frame pixels from the bitmap. 

    class MotionDetectorVideoView extends VideoView {
public Bitmap mFrameBitmap;
...
    @Override
    public void draw(Canvas canvas) {
        // set your own member bitmap to canvas..
        canvas.setBitmap(mFrameBitmap);
        super.draw(canvas);
        // do whatever you want with mFrameBitmap. It now contains the frame.
        ...
        // Allocate `buffer` big enough to hold the whole frame.
        mFrameBitmap.copyPixelsToBuffer(buffer);
        ...
    }
}

I don't know whether this will work. Avoid doing heavy calculation in draw, start a thread there.

halfer
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Ron
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  • How can i get raw pixels of the drawn canvas ? couldn't find anything in their API about it. – Danpe Dec 02 '12 at 18:57
  • There is `public void copyPixelsToBuffer (Buffer dst)` in Bitmap class. documentation here : http://developer.android.com/reference/android/graphics/Bitmap.html#copyPixelsToBuffer(java.nio.Buffer) – Ron Dec 03 '12 at 04:24
  • Yes, but how to get the Bitmap from the Canvas? – Danpe Dec 03 '12 at 09:54
  • You already have the bitmap reference in `mFrameBitmap`.. Create the bitmap in constructor.. See the edit above.. – Ron Dec 03 '12 at 12:54
  • So you say that when i call `super.draw(canvas)` it draws on the current bitmap and not replacing with a new one ? And I'm able to call NDK calculation inside `draw` ? – Danpe Dec 03 '12 at 19:25
  • Haven't you tried it yet? Im not sure about that. Can do NDK calc if it doesnt slow down or flicker the video.. – Ron Dec 04 '12 at 05:21
  • Tried it.. `onDraw` doesn't even get called. – Danpe Dec 04 '12 at 12:56
  • What do you mean by "nothing"? – Ron Dec 07 '12 at 16:51
  • I'm on debug mode, breakpoint inside the `public void draw(Canvas canvas)` with `@Override` before, and the debugger doesn't get there.. – Danpe Dec 07 '12 at 16:54
  • Doesn't work ... Set Bitmap is a not supported operation for Video view... Because it's not a simple canvas , it's HardwareCanvas ! java.lang.UnsupportedOperationException at android.view.HardwareCanvas.setBitmap(HardwareCanvas.java:39) at com.zemingo.MyVideoView.dispatchDraw(MyVideoView.java:38) – Ivelius Oct 15 '13 at 13:03
1

In your case I would use the Camera Preview instead the VideoView, if you are working with live motion, not recorded videos. You can use a Camera Preview Callback to catch everyframe captured by your camera. This callback implements :

onPreviewFrame(byte[] data, Camera camera)
Called as preview frames are displayed.

Which I think it could be useful for you.

http://developer.android.com/reference/android/hardware/Camera.PreviewCallback.html

Tell if that is what you are searching for.

Good luck.

JasJar
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