GstVideoAlphaMode

When input and output have alpha, it will be copied. When the input has no alpha, alpha will be set to #GST_VIDEO_CONVERTER_OPT_ALPHA_VALUE

set all alpha to #GST_VIDEO_CONVERTER_OPT_ALPHA_VALUE

multiply all alpha with #GST_VIDEO_CONVERTER_OPT_ALPHA_VALUE. When the input format has no alpha but the output format has, the alpha value will be set to #GST_VIDEO_CONVERTER_OPT_ALPHA_VALUE