[export frame to jpeg] #kotlin #android #media #video

MainActivity.kt

// the path of output folder
private val EXPORT_FOLDER = "/your/folder/path/"

// this is a trigger for enabling/disabling the function
private var exportFrameToJpeg = false 

// a counter which acculating the number of video frame
private var nbFrame = 0

// the prepare function of decoder
private fun prepare() {
  // do other things for video decoder
  
  // if we want to export frames, decoder won't export the frames to surface
  if (exportFrameToJpeg)
    codec!!.configure(inputFormat, null, null, 0)
  else
    codec!!.configure(inputFormat, Surface(surfaceTexture), null, 0)
    
  // ...
}

private fun decode() {
  // dealing the buffers of decoder
  when (val index = codec!!.dequeueOutputBuffer(bufferInfo, WAIT_TIME)) {
    MediaCodec.INFO_OUTPUT_FORMAT_CHANGED -> Log.i(TAG, "INFO_OUTPUT_FORMAT_CHANGED")
    MediaCodec.INFO_TRY_AGAIN_LATER -> Log.i(TAG, "INFO_TRY_AGAIN_LATER")
    MediaCodec.INFO_OUTPUT_BUFFERS_CHANGED -> Log.i(TAG, "INFO_OUTPUT_BUFFERS_CHANGED")
    else -> {
      if (exportFrameToJpeg)
      	saveBitmap(index)
        
      // do something for the frames
      
      // release buffer
      if (exportFrameToJpeg)
        codec!!.releaseOutputBuffer(index, false) // don't rend the frames
      else
        codec!!.releaseOutputBuffer(index, true) // we want it to be rendered if it is true
    }
  }
}

private fun saveBitmap(index: Int) {
    val image = codec!!.getOutputImage(index)

    try {
        val path = Environment.getExternalStorageDirectory().toString() + EXPORT_FOLDER
        val testFile = File(path)
        if (!testFile.exists())
            testFile.mkdir()
        var imgName = nbFrame.toString()
        when {
            nbFrame < 10 -> imgName = "000$nbFrame"
            nbFrame < 100 -> imgName = "00$nbFrame" 
            nbFrame < 1000 -> imgName = "0$nbFrame"
        }
      
        val fileName = "Img_$imgName.jpg"
        val file = File(path, fileName)
        val out = FileOutputStream(file)
        val yuvImage = YuvImage(yuv420TONv21(image!!), 
                                ImageFormat.NV21, 
                                getWidth(), 
                                getHeight(), 
                                null)
        yuvImage.compressToJpeg(Rect(0, 0, getWidth(), getHeight()), 80, out)
        ++nbFrame
    } catch (e: java.lang.Exception) {
        e.printStackTrace()
    }
}

private fun yuv420ToNv21(image: Image): ByteArray {
  val yBuffer = image.planes[0].buffer
  val uBuffer = image.planes[1].buffer
  val vBuffer = image.planes[2].buffer
  val ySize = yBuffer.remaining()
  val uSize = uBuffer.remaining()
  val vSize = vBuffer.remaining()
  
  val nv21 = ByteArray(ySize + uSize + vSize)
  
  // U and V are swapped
  yBuffer.get(nv21, 0, ySize)
  vBuffer.get(nv21, ySize, vSize)
  uBuffer.get(nv21, ySize + vSize, uSize)
  
  return nv21
}