screenshot android presentation display/surface

问题

I would like to make "instant" screenshots of an Presentation object in Android. My Presentation normally renders to a virtual display (PRIVATE) which is backed by the surface from a MediaRecorder that is setup to record video. Recording the presentation as a video works great.

mMediaRecorder = new MediaRecorder();
mMediaRecorder.setAudioSource(MediaRecorder.AudioSource.MIC);
mMediaRecorder.setVideoSource(MediaRecorder.VideoSource.SURFACE);
mMediaRecorder.setOutputFormat(MediaRecorder.OutputFormat.MPEG_4);
mMediaRecorder.setOutputFile(getScratchFile().getAbsolutePath());
mMediaRecorder.setVideoEncodingBitRate(bitrateInBitsPerSecond);
mMediaRecorder.setVideoFrameRate(30);
mMediaRecorder.setVideoSize(mVideoSize.getWidth(), mVideoSize.getHeight());
mMediaRecorder.setVideoEncoder(MediaRecorder.VideoEncoder.H264);
mMediaRecorder.setAudioEncoder(MediaRecorder.AudioEncoder.AAC);

mVirtualDisplay = mDisplayManager.createVirtualDisplay(
        DISPLAY_NAME, // string name required
        mVideoSize.getWidth(),
        mVideoSize.getHeight(),
        160, // screen densityDpi, not sure what it means in this context
        mMediaRecorder.getSurface(), // the media recorder must already be {@code prepare()}'d
        DisplayManager.VIRTUAL_DISPLAY_FLAG_OWN_CONTENT_ONLY); // only we can use it

mPresentation = new MyPresentation(getActivity(), mVirtualDisplay().getDisplay());

How can I get a screenshot of the mMediaRecorder.getSurface() at any time, including when the mMediaRecorder is setup but not recording?

I've tried a number of methods related to the view.getDrawingCache() on the Presentation root view object and I only get clear/black output. The presentation itself contains TextureView objects, which I'm guessing are messing up this strategy. I also tried using an ImageReader with the DisplayPreview of the mMediaRecorder but it receives no images in the callback -- ever

mMediaRecorder.setDisplayPreview(mImageReader.getSurface());

I'd really like some way to mirror the Surface which backs the presentation into an ImageReader and use that as a consumer, I just can't see how to "mirror" one surface as a producer into another "consumer" class. It seems there should be an easy way with SurfaceFlinger.

回答1:

Surfaces are the producer end of a producer-consumer data structure. A producer can't pull data back out of the pipe, so attempting to read frames back from a Surface isn't possible.

When feeding MediaCodec or MediaRecorder, the consumer end is in a different process (mediaserver) that manages the media hardware. For a SurfaceView, the consumer is in SurfaceFlinger. For a TextureView, both ends are in your app, which is why you can easily get a frame from TextureView (call getBitmap()).

To intercept the incoming data you'd need to have both producer and consumer in the same process. The SurfaceTexture class (also known as "GLConsumer") provides this -- it's a consumer that converts the frames it receives into GLES textures.

So the idea would be to create a SurfaceTexture, create a new Surface from that (you'll note that Surface's only public constructor takes a SurfaceTexture), and pass that Surface as the virtual display output Surface. Then as frames come in you "forward" them to the MediaRecorder by rendering the textures with OpenGL ES.

This is not entirely straightforward, especially if you haven't worked with OpenGL ES before. Various examples can be found in Grafika (e.g. "texture from camera" and "record GL app").

I don't know if setDisplayPreview() is expected to work for anything other than Camera.

来源：https://stackoverflow.com/questions/32163769/screenshot-android-presentation-display-surface

标签

android

surfaceview

android-mediarecorder