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Is it possible to use SurfaceComposerClient to get screenshots, the way MediaCodec does with createInputSurface().

I cant use MediaCodec for that because I need raw video and not encoded data.

since 4.3 it seems that ScreenshotClient cant do multiple screenshots.

Ilya Gazman
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jacob
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2 Answers2

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Yes, assuming you're running as shell or root, and you don't mind using non-public native APIs (i.e. you don't care if your app breaks every time a new version of the OS rolls out).

The canonical example is screenrecord, introduced in Android 4.4. It creates a virtual display and directs the output to a Surface. For normal operation a MediaCodec input surface receives the output. For the "bugreport" mode introduced in screenrecord v1.1, the output goes to a GLConsumer (roughly equivalent to a SurfaceTexture), which is rendered to a Surface with overlaid text.

fadden
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  • in screenrecord 1.1 Overlay, What do I need to do to get the image raw bytes from the outputSurface (IGraphicBufferProducer) ? – jacob Jan 15 '14 at 00:20
  • In `setup_l()`, Overlay creates an EGL window surface for the IGraphicBufferProducer. That feeds into the video encoder. If you instead create a pbuffer surface, you can then use `glReadPixels()` to extract the data after the texture blit in `processFrame_l()`. – fadden Jan 15 '14 at 00:50
  • I have finally got it to work, but it slows the device terribly, unlike MediaCodec that doesn't slow at all ( and it also does encoding what should of been slower than just grab raw data, no ? ). Any way I can speed it up ? – jacob Jan 15 '14 at 15:53
  • Something I learned recently is that, if EGL isn't configured with an alpha plane, `glReadPixels(GL_RGBA)` can take an absurdly long time on certain devices (177ms vs. 6ms). In `eglSetupContext()` (or wherever you're configuring EGL for your pbuffer), below `EGL_BLUE_SIZE, 8,` add `EGL_ALPHA_SIZE, 8,` and see if that helps. – fadden Jan 15 '14 at 16:24
  • EGL_ALPHA_SIZE, 8, didnt help would you mind taking a look at my code, maybe I am doing glReadPixels() in the wong place. https://dl.dropboxusercontent.com/u/36894441/EglWindow.cpp https://dl.dropboxusercontent.com/u/36894441/Overlay.cpp – jacob Jan 15 '14 at 16:42
  • In `createWindow()`, use `mWidth` and `mHeight` in the `pbufferAttribs` so it doesn't have to scale (I suspect you're scaling the display resolution to 1280x800, then scaling it back to display res when extracting... unless you're on a device with a 1280x800 display). Before we go too far down this road, you should bracket the `glReadPixels()` call with `systemTime(CLOCK_MONOTONIC)` calls to see just how long each invocation is taking... maybe the performance problem is elsewhere. (Maybe install https://github.com/google/grafika and run the "glReadPixels speed test"?) – fadden Jan 15 '14 at 17:51
  • I am using a display of 1280x800 - nexus 7 ( hard coded just for tests ) , I added a time test around glReadPixels and got avg of 220 ms per call. perhaps I should be using a Pixel Buffer Object ? – jacob Jan 15 '14 at 18:09
  • let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/45308/discussion-between-jacob-and-fadden) – jacob Jan 15 '14 at 18:10
  • Got my Nexus 7 (2012) updated. Grafika reports ~200ms for a 1280x720 frame, consistent with your results. Ugh. – fadden Jan 15 '14 at 18:21
  • I am trying EGL_KHR_image_base with no success, can you take a look at this: http://stackoverflow.com/questions/21151259/replacing-glreadpixels-with-egl-khr-image-base-for-faster-pixel-copy – jacob Jan 17 '14 at 12:14
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There's a bug in Android 4.3 (see issues 59649 or 60638 on the Android Open Source Project Issue Tracker) which means ScreenshotClient can't be used to take more than one screenshot.

Christopher Fraser
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