fluent-ffmpeg size/padding attempt 1

gistfile1.js

function getScalePadFilters(width, height, aspect, color) {
  /*
    let a be the input aspect ratio, A be the requested aspect ratio

    if a > A, padding is done on top and bottom
    if a < A, padding is done on left and right
   */

  return [
    /*
      In both cases, we first have to scale the input to match the requested size

        scale=
          ow=if(gt(a, A), width, height*a),
          oh=if(lt(a, A), height, width/a)
     */

    'scale=' +
      'ow=if(gt(a,' + aspect + '),' + width + ',' + height + '*a),' +
      'oh=if(lt(a,' + aspect + '),' + height + ',' + width + '/a)',

    /*
      Then we pad the scaled input to match the target size

        pad=
          w=width,
          h=height,
          x=if(gt(a, A), 0, (width - height*a)/2),
          y=if(lt(a, A), 0, (height - width/a)/2)

      (here we can replace height*a by iw and width/a by ih as they are the size
       of the frames the scaling filter outputs).
     */

    'pad=' +
      'w=' + width + ',' +
      'h=' + height + ',' +
      'x=if(gt(a,' + aspect + '),0,(' + width + '-iw*a)/2),' +
      'y=if(lt(a,' + aspect + '),0,(' + height + '-ih/a)/2),' +
      'color=' + color
  ];
}

FfmpegCommand.prototype.getSizeFilters = function() {
  if (!this.options.video.size) {
    // No size requested

    if (this.options.video.aspect) {
      this.options.logger.warn('Ignoring aspect ratio as withSize() was not called');
    }

    if (this.options._applyAutopad) {
      this.options.logger.warn('Ignoring auto padding as withSize() was not called');
    }

    // TODO pixel aspect

    // Keep original size
    return [];
  }

  var fixedSize = this.options.video.size.match(/([0-9]+)x([0-9]+)/);
  var fixedWidth = this.options.video.size.match(/([0-9]+)x\?/);
  var fixedHeight = this.options.video.size.match(/\?x([0-9]+)/);
  var percentRatio = this.options.video.size.match(/\b([0-9]{1,3})%/);
  var width, height, aspect;

  if (percentRatio) {
    if (this.options.video.aspect) {
      this.options.logger.warn('Ignoring aspect ratio as withSize() was called with a percent ratio');
    }

    if (this.options._applyAutopad) {
      this.options.logger.warn('Ignoring auto padding as withSize() was called with a percent ratio');
    }

    // TODO pixel aspect

    return ['scale=iw*' + percentRatio[1] + '/100:ih*' + percentRatio[1] + '/100'];
  } else if (fixedSize) {
    width = fixedSize[1];
    height = fixedSize[2];
    aspect = width / height;

    if (this.options.video.aspect) {
      this.options.logger.warn('Ignoring aspect ratio as withSize() was called with a fixed size');
    }

    if (this.options._applyAutopad) {
      return getScalePadFilters(width, height, aspect, this.options.video.padcolor);
    }

    // TODO pixel aspect

    // No autopad requested, rescale to target size
    return ['scale=' + width + ':' + height];
  } else if (fixedWidth || fixedHeight) {
    if (this.options.video.aspect) {
      // Specified aspect ratio
      aspect = Number(this.options.video.aspect);
      if (isNaN(aspect)) {
        throw new Error('Invalid aspect ratio: ' + this.options.video.aspect);
      }

      width = fixedWidth ? fixedWidth[1] : Math.round(Number(fixedHeight[1]) * aspect);
      height = fixedHeight ? fixedHeight[1] : Math.round(Number(fixedWidth[1]) / aspect);

      if (this.options._applyAutopad) {
        return getScalePadFilters(width, height, aspect, this.options.video.padcolor);
      }

      // TODO pixel aspect

      // No autopad requested, rescale to target size
      return ['scale=' + width + ':' + height];
    } else {
      // Keep input aspect ratio

      if (this.options._applyAutopad) {
        this.options.logger.warn('Ignoring auto padding as input aspect is kept');
      }

      // TODO pixel aspect

      if (fixedWidth) {
        return ['scale=' + fixedWidth[1] + ':-1'];
      } else {
        return ['scale=-1:' + fixedHeight[1]];
      }
    }
  } else {
    throw new Error('Invalid size specified: ' + this.options.video.size);
  }
};