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• Fast green screen video processing on android device

  17 March 2015, by Si-N

  I have written an app in iOS that takes two video sources, one with moving character on a green screen and any other video. The program then uses the GPUImage framework to add a chroma key shader via OpenGL ES 2 and then merges each frame (so the bottom frame now shows where the green pixels are) and outputs to a new video file. This happens very quickly, faster than real time.

  I have now been tasked with porting the app to Android. I thought it would be fairly straightforward. After doing some research I think I am wrong. There is an Android port of GPUImage but it does not handle video at the moment. I have done some research and come up with a very basic idea.

  I was wondering if you think this approach is feasible:

  Convert one video file to match resolution and type of other video using ffmpeg or JavaCV wrappers.

  Read frame by frame of each video using ffmpeg as MediaMetadataRetriever is very slow and convert into some RGB format. Use shader to apply chroma key effect so both frames are merged.

  Use ffmpeg to output result to a new file.

  This sounds slow, but if it sounds feasible I will try it out. I am not at all sure about making sure the 2 video resolutions / bitrate etc match. One video will be fixed at 1280 * 720 and the other video source will come from the camera on the device so will be variable. Also I think ffmpeg means using NDK which is a whole world of pain I wanted to avoid.

  I have a headache thinking about it. Any advice would be greatly appreciated.

• Android: Recording and Streaming at the same time

  29 March 2016, by Bruno Siqueira

  This is not really a question as much as it is a presentation of all my attempts to solve one of the most challenging functionalities I was faced with.

  I use libstreaming library to stream realtime videos to Wowza Server and I need to record it at the same time inside the SD card. I am presenting below all my attempts in order to collect new ideias from the community.

  Copy bytes from libstreaming stream to a mp4 file

  Development

  We created an interception in libstreaming library to copy all the sent bytes to a mp4 file. Libstreaming sends the bytes to Wowza server through a LocalSocket. It users MediaRecorder to access the camera and the mic of the device and sets the output file as the LocalSocket’s input stream. What we do is create a wrapper around this input stream extending from InputStream and create a File output stream inside it. So, every time libstreaming executes a reading over the LocaSocket’s input stream, we copy all the data to the output stream, trying to create a valid MP4 file.

  Impediment

  When we tried to read the file, it is corrupted. We realized that there are meta information missing from the MP4 file. Specifically the moov atom. We tried to delay the closing of the streaming in order to give time to send this header (this was still a guessing) but it didn’t work. To test the coherence of this data, we used a paid software to try to recover the video, including the header. It became playable, but it was mostly green screen. So this became an not trustable solution. We also tried using "untrunc", a free open source command line program and it couldn’t even start the recovery, since there was no moov atom.

  Use ffmpeg compiled to android to access the camera

  Development

  FFMPEG has a gradle plugin with a java interface to use it inside Android apps. We thought we could access the camera via command line (it is probably in "/dev/video0") and sent it to the media server.

  Impediment

  We got the error "Permission Denied" when trying to access the camera. The workaround would be to root the device to have access to it, but it make the phones loose their warranty and could brick them.

  Use ffmpeg compiled to android combined with MediaRecorder

  Development

  We tried to make FFMPEG stream a mp4 file being recorded inside the phone via MediaRecorder

  Impediment

  FFMPEG can not stream MP4 files that are not yet done with the recording.

  Use ffmpeg compiled to android with libstreaming

  Development

  Libstreaming uses LocalServerSocket as the connection between the app and the server, so we thought that we could use ffmpeg connected with LocalServerSocket local address to copy the streaming directly to a local file inside the SD card. Right after the streaming started, we also ran the ffmpeg command to start recording the data to a file. Using ffmpeg, we believed that it would create a MP4 file in the proper way, which means with the moov atom header included.

  Impediment

  The "address" created is not readable via command line, as a local address inside the phone. So the copy is not possible.

  Use OpenCV

  Development

  OpenCV is an open-source, cross-platform library that provides building blocks for computer vision experiments and applications. It offers high-level interfaces for capturing, processing, and presenting image data. It has their own APIs to connect with the device camera so we started studding it to see if it had the necessary functionalities to stream and record at the same time.

  Impediment

  We found out that the library is not really defined to do this, but more as image mathematical manipulation. We got even the recommendation to use libstreaming (which we do already).

  Use Kickflip SDK

  Development

  Kickflip is a media streaming service that provides their own SDK for development in android and IOS. It also uses HLS instead of RTMP, which is a newer protocol.

  Impediment

  Their SDK requires that we create a Activity with camera view that occupies the entire screen of the device, breaking the usability of our app.

  Use Adobe Air

  Development

  We started consulting other developers of app’s already available in the Play Store, that stream to servers already.

  Impediment

  Getting in touch with those developers, they reassured that would not be possible to record and stream at the same time using this technology. What’s more, we would have to redo the entire app from scratch using Adobe Air.

  UPDATE

  Webrtc

  Development

  We started using WebRTC following this great project. We included the signaling server in our NODEJS server and started doing the standard handshake via socket. We were still toggling between local recording and streaming via webrtc.

  Impediment

  Webrtc does not work in every network configuration. Other than that, the camera acquirement is all native code, which makes a lot harder to try to copy the bytes or intercept it.

• Set a Device Camera as Source for OpenCVFrameGrabber

  2 July 2018, by Dario Figliuzzi

  How can i set the camera of my android device as source for OpenCVFrameGrabber class?
  The library is org.bytedeco.javacv.OpenCVFrameGrabber;.

  The part of the code:

  private static final int CAMERA_SRC = 0;
  
  OpenCVFrameGrabber= OpenCVFrameGrabber.createDefault(CAMERA_SRC);
  
  OpenCVFrameGrabber.start();

  In this way the laptop camera is setted.
  Is there an easy way to set the camera of the android device?