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• Fast green screen video processing on android device

  17 mars 2015, par 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.

• checkasm : Implement helpers for defining and checking padded rects

  21 mars, par Martin Storsjö

  checkasm : Implement helpers for defining and checking padded rects
  This backports similar functionality from dav1d, from commits
  
  35d1d011fda4a92bcaf42d30ed137583b27d7f6d and
  
  d130da9c315d5a1d3968d278bbee2238ad9051e7.
  This allows detecting writes out of bounds, on all 4 sides of
  
  the intended destination rectangle.
  The bounds checking also can optionally allow small overwrites
  
  (up to a specified alignment), while still checking for larger
  
  overwrites past the intended allowed region.
  Signed-off-by : Martin Storsjö <martin@martin.st>
  

  • [DH] tests/checkasm/checkasm.c
  • [DH] tests/checkasm/checkasm.h

• ffmpeg node js s3 stream screenshots qestion

  20 octobre 2015, par user3564443

  On my Node js server I need get video from s3, generate thumbnail for it, set thumbnail to s3, without saving video or thumbnail on my server. So I need to use streams for this. For thumbnail generation I use fluent-ffmpeg.

  Is it possible to get screenshots from streams using fluent-ffmpeg ?

  Is the correct way to intercept s3 getObject stream, that there was no need to download full video ?

  var config = require('../config');
  
  var AWS = require('aws-sdk');
  
  AWS.config.update({
  
    accessKeyId: config.AWS_accessKeyId,
  
    secretAccessKey: config.AWS_secretAccessKey,
  
    region: 'eu-west-1'
  
  });
  
  var s3 = new AWS.S3();
  
  var fs = require('fs');
  
  var ffmpeg = require('fluent-ffmpeg');
  
  
  
  exports.generateVideoThumbnail = function(fileId, url, done) {
  
    var params = {
  
      Bucket: config.AWS_bucket,
  
      Key: url
  
    };
  
    var input = s3.getObject(params);
  
    var stream = fs.createWriteStream('./screenshot.png');
  
    return ffmpeg(input).screenshots({
  
      timestamps: ['0.1', '0.2'],
  
      size: '200x200'
  
    }).output('./screenshot.png').output(stream).on('error', function(err) {
  
      return done(err);
  
    }).on('end', function() {
  
      input.close();
  
      var _key = "files/" + fileId + "/thumbnail.png";
  
      return s3.putObject({
  
        Bucket: config.AWS_bucket,
  
        Key: _key,
  
        Body: stream,
  
        ContentType: 'image/jpeg'
  
      }, function(err) {
  
        return done(err);
  
      });
  
    });
  
  };