视频表面视图的屏幕截图显示黑屏

Question

<?php
$mapping = array(
    100 => 'emission_a',
    120 => 'emission_b',
    150 => 'emission_c',
    165 => 'emission_d',
    185 => 'emission_e',
    225 => 'emission_f'
);

$cssClass = 'emission_g'; // default class if $emission is > 225

foreach ($mapping as $limit => $class) {
    if ($emission <= $limit) {
        $cssClass = $class;
        break;
    }
}

此应用程序从互联网流视频并在surfaceview中显示它。在视图中放置一个按钮，以获取视频的屏幕截图。但是，它始终仅显示黑屏..任何帮助？