使用 Matrix android java 进行视频裁剪

Posted 2023-02-25

【中文标题】使用 Matrix android java 进行视频裁剪

【英文标题】：Video cropping w/ Matrix android java

【发布时间】：2019-02-22 19:17:51

【问题描述】：

任务是按给定点（如矩形）裁剪视频并显示裁剪后的视频。code 用于裁剪视频（0, 0, videoWidth/2, videoHeight）的first halh。但是当我尝试显示第二个（videoWidth/2, 0, videoWidth, videoHeight）时，that is what was displayed.

视频显示在 FrameLayout 内的 TextureView 上。

不起作用的部分：

private void updateTextureViewSize(int ax, int ay, int bx, int by) 
    float scaleX;
    float scaleY;

    //proportions between screen and frame dimensions
    scaleX = mVideoWidth / mDisplayWidth;
    scaleY = mVideoHeight / mDisplayHeight;

    float scaleRegionW = mVideoWidth / Math.abs(ax - bx);
    float scaleRegionH = mVideoHeight / Math.abs(ay - by);
    float scaleRegion = scaleRegionW < scaleRegionH ? scaleRegionW : scaleRegionH;

    Matrix matrix = new Matrix();
    if (scaleX > scaleY) 
        matrix.setScale(scaleRegion / scaleY, scaleRegion);
        matrix.postTranslate(-ax * (int) scaleRegion / scaleY, -ay * scaleRegion / scaleY);
     else 
        matrix.setScale(scaleRegion, scaleRegion / scaleX);
        matrix.postTranslate(-ax * scaleRegion / scaleX, -ay * scaleRegion / scaleX);
    
    mTextureView.setTransform(matrix);
    mTextureView.setLayoutParams(new FrameLayout.LayoutParams((int) mDisplayWidth, (int) mDisplayHeight));

【参考方案1】：

Dmitry Yacenko找到了答案。 完整的code。

通过给定点（ax、ay、bx、xy）裁剪视频的一种简单方法是：

    float scaleX = mDisplayWidth / mVideoWidth, scaleY = mDisplayHeight / mVideoHeight; 
    //proportions between screen and frame dimensions
    float scale = mDisplayHeight / Math.abs(by - ay);
    Matrix matrix = new Matrix();
    matrix.reset();
    matrix.setScale(scale / scaleX, scale / scaleY);
    //scaling video
    matrix.postTranslate(-scale * ax, -scale * ay);
    //move video, so the needed part of it will be displayed properly
    mTextureView.setLayoutParams(new FrameLayout.LayoutParams((int) mDisplayWidth, (int) mDisplayHeight));
    mTextureView.setTransform(matrix);
    //updating the Texture view